Iron oxide Fe2O3, Fe3O4

spore: profile
id: iron-oxide
spore_version: 0.2
family: oxide-ceramics
name: Iron oxide
abbreviation: Fe2O3, Fe3O4
role: magnetic and pigment oxides (hematite, magnetite, ferrite magnets and cores)
category: ceramics
type: oxides
summary: |
  Iron oxides are the oxides of iron. Hematite (Fe2O3) is a red, antiferromagnetic oxide with a Néel temperature of about 948 K. Magnetite (Fe3O4) is a ferrimagnetic spinel with a Curie temperature of 858 K. Ferrites add a second metal oxide: hard strontium hexaferrite (SrO.6Fe2O3) is the most used permanent magnet family, at about 85 wt.% of the permanent magnet market by one review, and soft MnZn ferrites such as TDK N87 carry flux in power transformers. Bismuth ferrite and samarium ferrite are related perovskite-type oxides that are only mentioned here. Iron oxide pigments are colour stable and are used in paint, coatings and concrete. Hematite is also widely present on the surface of Mars.
best_for: Cheap, corrosion-resistant magnets and power-transformer cores, and colour-stable pigments
weakest_at: Magnetic strength per volume, which is lower than NdFeB or SmCo magnets, and brittleness of sintered ferrite parts
identity:
  formula: Fe2O3 (hematite); Fe3O4 (magnetite); SrO.6Fe2O3 (strontium ferrite)
  cas: 1309-37-1
  crystal_system: corundum type (hematite)
  source: arxiv-oxidation-iron-oxide
  where: Introduction, paragraph on the hematite crystal structure (isostructural with corundum, oxygen closely packed around the Fe3+ cations); CAS number in the CAS section of the PubChem record (CID 518696)
tags:
  environments:
    - mars-surface
  stresses:
    - extreme-heat
  applications:
    - electronics-and-chips
    - mechanisms
properties:
  - benchmark: density
    label: Density, iron(III) oxide (Fe2O3)
    value: 5.24
    unit: g/cm3
    scope: material
    conditions:
      form: iron(III) oxide, PubChem record CID 518696
      phase: not stated in the record
    method: Experimental value printed in the PubChem record; other entries in the same section print 5.25 g/cu cm
    status: ground
    source: pubchem-fe2o3
    where: Chemical and Physical Properties, Experimental Properties, Density
  - benchmark: neel_temperature
    label: Néel temperature, hematite (alpha-Fe2O3)
    value: 948
    unit: K
    scope: material
    conditions:
      phase: alpha-Fe2O3, bulk
      basis: value quoted for bulk hematite in the introduction of the paper
    method: Value stated in the introduction of a 2025 arXiv paper on hematite nanospindles
    status: ground
    source: arxiv-hematite-nanospindles
    where: Introduction, paragraph on weak ferromagnetism (Néel temperature TN of ca. 948 K)
  - benchmark: morin_transition_temperature
    label: Morin transition temperature, bulk hematite
    value: 250
    value_high: 260
    bound: range
    unit: K
    scope: material
    conditions:
      phase: alpha-Fe2O3, bulk
      note: spin reorientation on cooling; smaller particles shift it lower
    method: Range stated in the introduction of the paper for bulk hematite
    status: ground
    source: arxiv-hematite-nanospindles
    where: Introduction, paragraph on the Morin transition (typically between 250 K and 260 K)
  - benchmark: curie_temperature
    label: Curie temperature, magnetite (Fe3O4)
    value: 858
    unit: K
    scope: material
    conditions:
      phase: magnetite, Fe3O4
      basis: value quoted in the introduction of the paper
    method: Value stated in the introduction of a 2018 arXiv paper on magnetic properties near the Verwey transition
    status: ground
    note: A 2022 review gives about 850 K for the same transition, consistent with this value.
    source: arxiv-magnetite-verwey
    where: Introduction, first paragraphs (high Curie temperature (858 K))
  - benchmark: verwey_transition_temperature
    label: Verwey transition temperature, magnetite (Fe3O4)
    value: 125
    unit: K
    scope: material
    conditions:
      phase: magnetite, Fe3O4, bulk
      note: the review says it drops to about 120 K for 20 nm particles
    method: Value stated in an open-access review of the magnetite trimeron bond
    status: ground
    source: pmc-magnetite-review
    where: Introduction and magnetite section (Verwey transition at TV of about 125 K)
  - benchmark: curie_temperature
    label: Curie temperature, strontium hexaferrite (SrFe12O19)
    value: 746
    unit: K
    scope: material
    conditions:
      phase: SrFe12O19, M-type strontium hexaferrite
      basis: room-temperature intrinsic parameter table
    method: Value in Table 1 of an open-access review on hard hexaferrite magnets (from its reference 34)
    status: ground
    source: arxiv-hexaferrite-review
    where: Table 1 (intrinsic magnetic parameters at room temperature), row SrFe12O19, TC column
  - benchmark: saturation_magnetization
    label: Saturation magnetization, strontium hexaferrite (SrFe12O19)
    value: 72
    unit: Am2/kg
    scope: material
    conditions:
      phase: SrFe12O19
      temperature: room temperature
    method: Value in Table 1 of the same review (from its reference 34)
    status: ground
    source: arxiv-hexaferrite-review
    where: Table 1, row SrFe12O19, Ms column
  - benchmark: saturation_flux_density
    label: Saturation flux density Bs, strontium hexaferrite (SrFe12O19)
    value: 0.48
    unit: T
    scope: material
    conditions:
      phase: SrFe12O19
      temperature: room temperature
    method: Value in Table 1 of the same review (from its reference 34)
    status: ground
    source: arxiv-hexaferrite-review
    where: Table 1, row SrFe12O19, Bs column
  - benchmark: intrinsic_coercivity
    label: Theoretical maximum coercivity, strontium hexaferrite
    value: 594
    unit: kA/m
    scope: material
    conditions:
      phase: SrFe12O19, hypothetical single crystal with full alignment
      basis: theoretical limit from the large uniaxial anisotropy along the c axis
    method: Theoretical maximum quoted in the review; not a measured value
    status: calculated
    source: arxiv-hexaferrite-review
    where: Paragraph on the uniaxial anisotropy of the hexagonal lattice (theoretical maximum Hc of 594 kA/m)
  - benchmark: neel_temperature
    label: Néel temperature, bismuth ferrite (BiFeO3)
    value: 650
    unit: K
    scope: material
    conditions:
      phase: BiFeO3, bulk
      note: the same paper also gives 370 degC for the Néel temperature in another place
    method: Value stated in the introduction of a 2024 arXiv paper on magneto-electric coupling in bismuth ferrite
    status: ground
    source: arxiv-bfo-2406
    where: Introduction, paragraph on antiferromagnetic order (TN of about 650 K)
  - benchmark: curie_temperature
    label: Ferroelectric Curie temperature, bismuth ferrite (BiFeO3)
    value: 1100
    unit: K
    scope: material
    conditions:
      phase: BiFeO3, bulk
      order: ferroelectric
    method: Value stated in the introduction of the same 2024 arXiv paper
    status: ground
    source: arxiv-bfo-2406
    where: Introduction, paragraph on ferroelectric order (TC of about 1100 K)
  - benchmark: neel_temperature
    label: Néel temperature, samarium ferrite (SmFeO3)
    value: 680
    unit: K
    scope: material
    conditions:
      phase: SmFeO3 single crystal
      note: below this temperature it is a canted antiferromagnet with a weak ferromagnetic vector along c
    method: Value stated in the main text of a 2014 open-access paper on spin switching in SmFeO3
    status: ground
    source: sci-rep-smfeo3-2014
    where: Main text, paragraph on magnetization (Néel temperature TN = 680 K)
  - benchmark: saturation_flux_density
    label: Flux density Bs at 25 degC, MnZn power ferrite N87
    value: 490
    unit: mT
    scope: material
    conditions:
      grade: SIFERRIT N87, MnZn power ferrite
      field: H = 1200 A/m
      frequency: 10 kHz
      temperature: 25 degC
    method: Value in the material-properties table of the TDK ferrite catalogue
    status: ground
    source: tdk-ferrite-catalogue
    where: Material properties table (continued), N87 column, row Flux density BS (25 degC)
  - benchmark: saturation_flux_density
    label: Flux density Bs at 100 degC, MnZn power ferrite N87
    value: 390
    unit: mT
    scope: material
    conditions:
      grade: SIFERRIT N87, MnZn power ferrite
      field: H = 1200 A/m
      frequency: 10 kHz
      temperature: 100 degC
    method: Value in the material-properties table of the TDK ferrite catalogue
    status: ground
    source: tdk-ferrite-catalogue
    where: Material properties table (continued), N87 column, row Flux density BS (100 degC)
  - benchmark: curie_temperature
    label: Curie temperature, MnZn power ferrite N87
    value: 210
    bound: lower
    unit: °C
    scope: material
    conditions:
      grade: SIFERRIT N87, MnZn power ferrite
    method: Table value printed as a lower limit (above 210 degC)
    status: ground
    source: tdk-ferrite-catalogue
    where: Material properties table (continued), N87 column, row Curie temperature TC
  - benchmark: initial_permeability
    label: Initial permeability, MnZn power ferrite N87
    value: 2200
    unit: '-'
    scope: material
    conditions:
      grade: SIFERRIT N87, MnZn power ferrite
      temperature: 25 degC
    method: Value in the material-properties table of the TDK ferrite catalogue
    status: ground
    source: tdk-ferrite-catalogue
    where: Material properties table (continued), N87 column, row Initial permeability
  - benchmark: coercive_field
    label: Coercive field strength, MnZn power ferrite N87
    value: 21
    unit: A/m
    scope: material
    conditions:
      grade: SIFERRIT N87, MnZn power ferrite
      temperature: 25 degC
      frequency: 10 kHz
    method: Value in the material-properties table of the TDK ferrite catalogue
    status: ground
    source: tdk-ferrite-catalogue
    where: Material properties table (continued), N87 column, row Coercive field strength Hc (25 degC)
  - benchmark: density
    label: Density, MnZn power ferrite N87 (typical)
    value: 4850
    unit: kg/m3
    scope: material
    conditions:
      grade: SIFERRIT N87, MnZn power ferrite
      basis: typical value
    method: Typical value printed in the material-properties table of the TDK ferrite catalogue
    status: ground
    source: tdk-ferrite-catalogue
    where: Material properties table (continued), N87 column, row Density (typical values)
  - benchmark: remanence
    label: Remanence Br, hard ferrite grade 28/26 (minimum)
    value: 380
    unit: mT
    scope: material
    conditions:
      grade: Hard ferrite 28/26, anisotropic sintered
      basis: minimum value (min row) in the product table
    method: Minimum value printed in the magnetic-properties table of the thyssenkrupp product information
    status: ground
    source: thyssen-hard-ferrite
    where: Magnetic properties table, row Hard ferrite 28/26, Br column
  - benchmark: intrinsic_coercivity
    label: Intrinsic coercivity HcJ, hard ferrite grade 28/26 (minimum)
    value: 260
    unit: kA/m
    scope: material
    conditions:
      grade: Hard ferrite 28/26, anisotropic sintered
      basis: minimum value (min row) in the product table
    method: Minimum value printed in the magnetic-properties table of the thyssenkrupp product information
    status: ground
    source: thyssen-hard-ferrite
    where: Magnetic properties table, row Hard ferrite 28/26, HcJ column
  - benchmark: max_energy_product
    label: Maximum energy product BHmax, hard ferrite grade 28/26 (minimum)
    value: 28
    unit: kJ/m3
    scope: material
    conditions:
      grade: Hard ferrite 28/26, anisotropic sintered
      basis: minimum value (min row) in the product table
    method: Minimum value printed in the magnetic-properties table of the thyssenkrupp product information
    status: ground
    source: thyssen-hard-ferrite
    where: Magnetic properties table, row Hard ferrite 28/26, BHmax column
  - benchmark: remanence_temperature_coefficient
    label: Temperature coefficient of remanence TK(Br), hard ferrite grades
    value: -0.2
    unit: '%/K'
    scope: material
    conditions:
      grade: hard ferrite, all grades in the table (28/26 shown)
      note: remanence falls as the magnet warms; HcJ rises by 0.4 %/K
    method: Coefficient printed in the magnetic-properties table of the thyssenkrupp product information
    status: ground
    source: thyssen-hard-ferrite
    where: Magnetic properties table, TK(Br) column
  - benchmark: density
    label: Density, sintered hard ferrite
    value: 4.7
    value_high: 4.9
    bound: range
    unit: g/cm3
    scope: material
    conditions:
      form: sintered hard ferrite, isotropic or anisotropic
    method: Range printed in the physical-properties table of the thyssenkrupp product information
    status: ground
    source: thyssen-hard-ferrite
    where: Physical properties table, Density column
  - benchmark: curie_temperature
    label: Curie temperature, hard ferrite magnets
    value: 450
    unit: °C
    scope: material
    conditions:
      material: hard ferrite (strontium or barium ferrite magnets)
    method: Value printed in the physical-properties section of the thyssenkrupp product information (Tc = 450 degC)
    status: ground
    source: thyssen-hard-ferrite
    where: Physical properties, Operating temperature and Curie temperature block
  - benchmark: max_service_temp
    label: Maximum operating temperature, hard ferrite magnets
    value: 250
    unit: °C
    scope: material
    conditions:
      material: hard ferrite magnets
      basis: manufacturer Tmax
    method: Value printed as Tmax in the physical-properties section of the thyssenkrupp product information; the Eclipse Magnetics sheet allows up to 300 degC in a few situations
    status: ground
    source: thyssen-hard-ferrite
    where: Physical properties, Operating temperature block (Tmax = 250 degC)
  - benchmark: elastic_modulus
    label: Young's modulus, sintered hard ferrite
    value: 120
    value_high: 180
    bound: range
    unit: kN/mm2
    scope: material
    conditions:
      form: sintered hard ferrite
    method: Range printed in the physical-properties table of the thyssenkrupp product information
    status: ground
    source: thyssen-hard-ferrite
    where: Physical properties table, Young's modulus column
  - benchmark: thermal_conductivity
    label: Thermal conductivity, sintered hard ferrite
    value: 5
    value_high: 10
    bound: range
    unit: W/m K
    scope: material
    conditions:
      form: sintered hard ferrite
    method: Range printed in the physical-properties table of the thyssenkrupp product information
    status: ground
    source: thyssen-hard-ferrite
    where: Physical properties table, Thermal conductivity column
  - benchmark: cte
    label: Coefficient of linear thermal expansion, hard ferrite
    value: 9.2
    value_high: 13.3
    bound: range
    unit: 10-6/K
    scope: material
    conditions:
      direction: in the magnetizing direction (9.2 to 10 normal to it)
      form: sintered hard ferrite
    method: Range printed in the physical-properties table of the thyssenkrupp product information
    status: ground
    source: thyssen-hard-ferrite
    where: Physical properties table, coefficient of linear thermal expansion columns
  - benchmark: specific_heat
    label: Heat capacity, hard ferrite
    value: 500
    value_high: 800
    bound: range
    unit: J/kg K
    scope: material
    conditions:
      form: sintered hard ferrite
    method: Range printed in the physical-properties table of the thyssenkrupp product information
    status: ground
    source: thyssen-hard-ferrite
    where: Physical properties table, Heat capacity column
  - benchmark: remanence
    label: Remanence Br, ferrite grade Y30 (typical range)
    value: 370
    value_high: 400
    bound: range
    unit: mT
    scope: material
    conditions:
      grade: Y30, Chinese-standard strontium ferrite grade
      basis: typical values from the grade table
    method: Typical range printed in the grade table of the Eclipse Magnetics ferrite datasheet
    status: ground
    source: eclipse-ferrite-datasheet
    where: Typical values table, row Y30, Br column
corrosion:
  - environment: Water and damp, wet or marine air (ferrite magnets)
    headline: Ferrite magnets do not rust in water, because their iron is already oxidized.
    effect: The Eclipse Magnetics datasheet says ferrite magnets are superb in damp, wet or marine environments and are corrosion free, because the iron is already in a stable oxidized form and cannot oxidize (rust) further in water.
    rating: none
    conditions:
      material: strontium ferrite magnets (SrO.6Fe2O3)
      exposure: damp, wet or marine environments
    source: eclipse-ferrite-datasheet
    where: Introduction, first page (paragraph on corrosion)
  - environment: Concentrated inorganic acids (hydrochloric, sulphuric, phosphorous, hydrofluoric, oxalic)
    headline: Permanent ferrite magnets are not resistant to concentrated inorganic acids.
    effect: The chemical resistance table lists hydrochloric, sulphuric, phosphorous, hydrofluoric and oxalic acids as not recommended for permanent ferrite magnets. Diluted nitric and sulphuric acids and acetic acid have only limited resistance.
    rating: severe
    conditions:
      material: permanent (hard) ferrite magnets
      basis: manufacturer chemical resistance table
    source: thyssen-hard-ferrite
    where: Chemical resistance section (not recommended and moderate effect columns)
  - environment: Water, petrol, organic solvents, caustic potash and soda lye
    headline: Ferrite magnets resist water, petrol, organic solvents and alkaline solutions.
    effect: The same chemical resistance table rates water, petrol, organic solvents, caustic potash solution and soda lye as good, and states that ferrite magnets are also resistant to oxidation and climatic influences.
    rating: none
    conditions:
      material: permanent (hard) ferrite magnets
      basis: manufacturer chemical resistance table
    source: thyssen-hard-ferrite
    where: Chemical resistance section (good column and text)
  - environment: Heat treatment in air from 250 degC to 900 degC (iron oxide nanoparticles)
    headline: Heated in air, the maghemite formed in iron oxide nanoparticles converts fully to hematite.
    effect: The paper finds that nanoparticles heat-treated at lower temperatures contain both maghemite and hematite, and that with increasing temperature the remaining maghemite converts completely to hematite. Crystallite size grows from 50 nm to 150 nm over the range. The paper gives no corrosion rate.
    rating: unknown
    conditions:
      atmosphere: air
      temperature_range: 250 degC to 900 degC
      form: iron oxide nanoparticles, heat treated
    source: arxiv-oxidation-iron-oxide
    where: Abstract (X-ray diffraction results); Results on crystallite size
  - environment: Sunlight and long-term outdoor exposure (pigments)
    headline: Iron oxide pigments stay colour stable, while many organic colourants fade in sunlight.
    effect: The USGS says iron oxide pigments are colour stable, low cost and nontoxic, and notes that many organic colourants fade over time from exposure to sunlight.
    rating: none
    conditions:
      use: iron oxide pigments in paint, coatings, concrete and plastics
      exposure: sunlight
    source: usgs-mcs2026-pigments
    where: Substitutes section
risks:
  hazards:
    - text: PubChem reports that 66.9% of company reports (2296 of 3433) do not meet GHS hazard criteria. Other notifications give H319 for eye irritation (18.5% of reports) and H411 for aquatic toxicity (12% of reports), with the signal word Warning.
      ghs:
        - H319
        - H411
      source: pubchem-fe2o3
      where: Safety and Hazards, GHS Classification (CID 518696)
    - text: Individual notifications in PubChem also give H315 (skin irritation), H318 (serious eye damage), H335 (respiratory irritation) and H372 (organ damage on repeated exposure, respiratory system), with the signal word Danger.
      ghs:
        - H315
        - H318
        - H335
        - H372
      source: pubchem-fe2o3
      where: Safety and Hazards, GHS Classification, second and third notification groups
    - text: The OSHA permissible exposure limit for iron oxide fume is 10 mg/m3 (8-hour time-weighted average). NIOSH gives 5 mg/m3 for iron oxide dust and fume as Fe.
      ghs: []
      source: pubchem-fe2o3
      where: Safety and Hazard Properties, OSHA Standards and NIOSH Recommendations
    - text: PubChem notes that iron dust or fume can cause siderosis, a benign lung condition, after prolonged exposure to high levels (10 to 700 mg/m3). There is no evidence that iron oxide alone causes fibrotic changes.
      ghs: []
      source: pubchem-fe2o3
      where: Safety and Hazards, Hazards Summary
  failure_risks:
    - mode: Cracking of sintered ferrite magnets
      trigger: Sharp edges, corners or cuts across the pressing direction
      consequence: The manufacturer says the material is brittle, so cracks and fractures can form; holes and grooves can only be made along the pressing direction.
      severity: moderate
      source: thyssen-hard-ferrite
      where: Magnet shapes section
    - mode: Loss of magnetism when hot
      trigger: Operation above the rated maximum of 250 degC, or close to the Curie temperature of 450 degC
      consequence: Remanence falls by 0.2 % per kelvin as the magnet warms, and the coercive field rises by 0.3 to 0.4 % as a rule of thumb. A few situations allow up to 300 degC, according to Eclipse Magnetics.
      severity: moderate
      source: thyssen-hard-ferrite
      where: Physical properties, temperature behaviour; Eclipse Magnetics introduction
  side_effects:
    - text: PubChem notes that the substance reacts with carbon monoxide, which can generate an explosion hazard. It is classed as noncombustible.
      affects: Process gas and enclosed spaces near furnaces
      source: pubchem-fe2o3
      where: Safety and Hazard Properties, Chemical Dangers; Fire Hazards
  handling:
    - text: Sweep spilled material into covered containers. If fume is released, ventilate the area. Use a particulate filter respirator adapted to the airborne concentration.
      source: pubchem-fe2o3
      where: Accidental Release Measures
    - text: The manufacturer says ferrite magnets are non-toxic when landfilled, are unaffected by incineration, and that contact with potable water is permitted.
      source: thyssen-hard-ferrite
      where: Toxicity section
  mitigations:
    - text: Keep airborne iron oxide dust and fume within the limits above, and use a particulate filter respirator where the concentration is high.
      source: pubchem-fe2o3
      where: Safety and Hazard Properties, OSHA and NIOSH limits; Accidental Release Measures
    - text: Keep hard ferrite magnets below their maximum operating temperature of 250 degC.
      source: thyssen-hard-ferrite
      where: Physical properties, Operating temperature (Tmax)
uses:
  - application: electronics-and-chips
    device: MnZn power ferrite cores for power transformers
    example: TDK lists N87 as a MnZn ferrite with a preferred application in power transformers, with an optimum frequency range of 25 to 500 kHz.
    source: tdk-ferrite-catalogue
    where: Material properties table (continued), N87 column, rows Preferred application and Optimum frequency range
  - application: mechanisms
    device: Permanent magnets in motors, generators and loudspeakers
    example: The Eclipse Magnetics datasheet says ferrite magnets are extremely popular in motor, generator, loudspeaker and marine designs, and the thyssenkrupp sheet calls hard ferrite the most cost-effective and widely used magnetic material.
    source: eclipse-ferrite-datasheet
    where: Introduction, paragraph on applications; thyssenkrupp sheet introduction (source thyssen-hard-ferrite)
  - application: structures
    device: Iron oxide pigments in concrete and construction products
    example: The USGS lists concrete and other construction products among the end uses of iron oxide pigments, which also go into paint, coatings, ferrites, plastics and rubber.
    source: usgs-mcs2026-pigments
    where: Domestic Production and Use paragraph
supply:
  - subject: Iron (ore feedstock for iron oxides); usable ore
    producers:
      - country: Australia
        share_percent: 37.7
        year: 2025
      - country: Brazil
        share_percent: 16.2
        year: 2025
      - country: India
        share_percent: 11.9
        year: 2025
      - country: China
        share_percent: 11.2
        year: 2025
    critical_lists:
      - list: 'USGS Final 2025 List of Critical Minerals (Federal Register notice 2025-19813, 60 minerals): iron and iron ore are not on the list'
        listed: false
    recycling: 'USGS iron ore chapter: ''None''. It refers readers to the Iron and Steel Scrap chapter.'
    substitutes:
      - 'USGS: the only source of primary iron is iron ore.'
    source: usgs-mcs2026-iron
    where: 'World Mine Production and Reserves table, usable ore, 2025e (world total 2,600,000 thousand t; shares calculated by Space Mushroom); Recycling; Substitutes. Critical list: Federal Register notice 2025-19813, the list of 60 minerals and the byproduct table (iron ore appears only as a byproduct host for rare earths).'
  - subject: 'Iron oxide pigments (US imports, 2021 to 2024: synthetic from China 44%, Germany 30%, Brazil 8%, Canada 6%; natural from Cyprus 51%, France 23%, Austria 18%)'
    producers: []
    critical_lists: []
    recycling: 'USGS: Recycling: None.'
    substitutes:
      - 'USGS: milled natural iron oxide pigments are the most commonly used natural minerals for pigments, and synthetic iron oxide pigments compete with them in many colours.'
    source: usgs-mcs2026-pigments
    where: Import Sources (2021 to 2024) and Substitutes. The world mine production table for pigments is partly garbled in the PDF text, so no producer shares are entered.
documents:
  - title: 'PubChem: Iron oxide (Fe2O3), CID 518696, properties, GHS classification and CAS number'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/518696
    year: 2026
  - title: 'USGS Mineral Commodity Summaries 2026: Iron Oxide Pigments'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-iron-oxide-pigments.pdf
    year: 2026
  - title: 'USGS Mineral Commodity Summaries 2026: Iron Ore'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-iron-ore.pdf
    year: 2026
  - title: 'Federal Register notice 2025-19813: Final 2025 List of Critical Minerals (USGS)'
    type: report
    url: https://public-inspection.federalregister.gov/2025-19813.pdf
    year: 2025
  - title: 'Hematite nanospindles: shape, magnetism and the Morin transition (arXiv 2505.14265)'
    type: paper
    url: https://arxiv.org/pdf/2505.14265
    year: 2025
  - title: Magnetism and the Trimeron Bond (magnetite review, open access, PMC9261838)
    type: paper
    url: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9261838/
    year: 2022
  - title: Evolution of magnetic properties in the vicinity of the Verwey transition in Fe3O4 (arXiv 1810.00538)
    type: paper
    url: https://arxiv.org/pdf/1810.00538
    year: 2018
  - title: Permanent magnets based on hard ferrite ceramics (arXiv 2310.02106)
    type: paper
    url: https://arxiv.org/pdf/2310.02106
    year: 2023
  - title: Magneto-electric decoupling in bismuth ferrite (arXiv 2406.16114)
    type: paper
    url: https://arxiv.org/pdf/2406.16114
    year: 2024
  - title: Temperature induced Spin Switching in SmFeO3 Single Crystal (Scientific Reports, open access)
    type: paper
    url: https://www.nature.com/articles/srep05960
    year: 2014
  - title: 'Mars: new insights and unresolved questions (arXiv 2112.00596)'
    type: paper
    url: https://arxiv.org/pdf/2112.00596
    year: 2021
  - title: Evolution of structural properties of iron oxide nanoparticles during temperature treatment from 250 to 900 degC (arXiv 1111.6204)
    type: paper
    url: https://arxiv.org/pdf/1111.6204
    year: 2011
  - title: TDK SIFERRIT ferrite and accessories catalogue, material characteristics (N87)
    type: datasheet
    url: https://www.tdk-electronics.tdk.com/download/519704/069c210d0363d7b4682d9ff22c2ba503/ferrites-and-accessories-db-130501.pdf
    year: 2013
  - title: 'thyssenkrupp Materials: Hard ferrite magnets, product information'
    type: datasheet
    url: https://ucpcdn.thyssenkrupp.com/_binary/UCPthyssenkruppBAMXSchulteMicrositeMagnettechnik/en/downloads/link-thyssenkruppMagnettechnik-Factsheet-ferrite-magnets.pdf
  - title: 'Eclipse Magnetics: Ferrite magnets (ceramic magnets) datasheet'
    type: datasheet
    url: https://www.eclipsemagnetics.com/site/assets/files/19602/ferrite_ceramic_datasheet.pdf
  - title: NIST Atomic Weights and Isotopic Compositions for All Elements
    type: database
    url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=Fe&all=all&ascii=html
gaps:
  - No flight, vacuum or radiation result for an iron oxide pigment or ferrite was found in a source read in this run. The space link is the Mars surface only.
  - Hematite melting point and magnetite saturation magnetization were not read in a source opened for this profile.
  - 'Samarium ferrite: only the Néel temperature (680 K) was read, in one open paper. Bismuth ferrite values come from one arXiv paper, and the review it cites was not read.'
  - Strontium and barium supply (producers of strontium and barium minerals) was not read, so the supply section covers iron ore and pigments only.
  - The EU critical raw materials list was not checked for iron oxide in this run; only the USGS 2025 list (Federal Register notice) was read.
  - Crustal abundance of iron was not read in a source opened for this profile.
  - 'Magnetite oxidation: the source gives phase changes and a temperature range, but no corrosion rate, so the rating is unknown.'
  - Electrical resistivity of N87 is printed in the TDK table, but its unit did not survive text extraction, so the value is not entered.
  - Hard ferrite property values are minimum guaranteed values (min rows) from one manufacturer, not typical values. The Eclipse Magnetics Y30 typical remanence is entered separately.
  - Hazard data rest on the PubChem record (company notifications) and the OSHA and NIOSH limits it prints. No supplier safety data sheet for an iron oxide pigment was read.
  - The Néel temperature and Morin transition of hematite come from one 2025 arXiv paper; a Wikipedia summary and search snippets gave similar values but were not used.
  - 'Non-canonical benchmark names used: neel_temperature, morin_transition_temperature, verwey_transition_temperature, saturation_magnetization, saturation_flux_density, remanence, intrinsic_coercivity, coercive_field, initial_permeability, max_energy_product, remanence_temperature_coefficient.'
  - Oxygen atomic weight is the NIST interval 15.99903 to 15.99977, rounded to 15.999; iron atomic weight is 55.845(2) as printed by NIST.
  - No images added. The LFP profile has three media entries, none sourced here.
sources:
  pubchem-fe2o3:
    title: PubChem compound record, Iron oxide (Fe2O3), CID 518696 (JSON view)
    id: CID 518696; CAS 1309-37-1
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/518696/JSON
    year: 2026
    kind: database
    license: public domain (NCBI)
  usgs-mcs2026-pigments:
    title: Mineral Commodity Summaries 2026, Iron Oxide Pigments
    id: USGS MCS 2026, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-iron-oxide-pigments.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  usgs-mcs2026-iron:
    title: Mineral Commodity Summaries 2026, Iron Ore
    id: USGS MCS 2026, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-iron-ore.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  usgs-fr-critical-2025:
    title: Final 2025 List of Critical Minerals (Federal Register notice 2025-19813, 7 November 2025)
    id: Federal Register 2025-19813, 90 FR 50494
    url: https://public-inspection.federalregister.gov/2025-19813.pdf
    year: 2025
    kind: report
    license: public domain (US government)
  arxiv-hematite-nanospindles:
    title: Insight into the Correlation of Shape and Magnetism of Hematite Nanospindles
    id: arXiv 2505.14265
    url: https://arxiv.org/pdf/2505.14265
    year: 2025
    kind: paper
    license: arXiv preprint (cited, not reproduced)
  pmc-magnetite-review:
    title: Magnetism and the Trimeron Bond (review of the magnetite Verwey transition)
    id: PMC9261838
    url: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9261838/
    year: 2022
    kind: paper
    license: open access (cited, not reproduced)
  arxiv-magnetite-verwey:
    title: Evolution of magnetic properties in the vicinity of the Verwey transition in Fe3O4
    id: arXiv 1810.00538
    url: https://arxiv.org/pdf/1810.00538
    year: 2018
    kind: paper
    license: arXiv preprint (cited, not reproduced)
  arxiv-hexaferrite-review:
    title: Permanent magnets based on hard ferrite ceramics
    id: arXiv 2310.02106
    url: https://arxiv.org/pdf/2310.02106
    year: 2023
    kind: paper
    license: arXiv preprint (cited, not reproduced)
  arxiv-bfo-2406:
    title: Magneto-electric decoupling in bismuth ferrite
    id: arXiv 2406.16114
    url: https://arxiv.org/pdf/2406.16114
    year: 2024
    kind: paper
    license: arXiv preprint (cited, not reproduced)
  sci-rep-smfeo3-2014:
    title: Temperature induced Spin Switching in SmFeO3 Single Crystal (Scientific Reports)
    id: Sci Rep, 2014, srep05960
    url: https://www.nature.com/articles/srep05960
    year: 2014
    kind: paper
    license: open access (cited, not reproduced)
  arxiv-mars-review:
    title: 'Mars: new insights and unresolved questions'
    id: arXiv 2112.00596
    url: https://arxiv.org/pdf/2112.00596
    year: 2021
    kind: paper
    license: arXiv preprint (cited, not reproduced)
  arxiv-oxidation-iron-oxide:
    title: 'Evolution of structural properties of iron oxide nanoparticles during temperature treatment from 250 to 900 degC: X-ray diffraction and Fe K-shell pre-edge X-ray absorption study'
    id: arXiv 1111.6204
    url: https://arxiv.org/pdf/1111.6204
    year: 2011
    kind: paper
    license: arXiv preprint (cited, not reproduced)
  tdk-ferrite-catalogue:
    title: TDK ferrites and accessories catalogue (SIFERRIT material characteristics, N87 and other MnZn grades)
    id: TDK catalogue, April 2013 print
    url: https://www.tdk-electronics.tdk.com/download/519704/069c210d0363d7b4682d9ff22c2ba503/ferrites-and-accessories-db-130501.pdf
    year: 2013
    kind: datasheet
    license: manufacturer catalogue (cited, not reproduced)
  thyssen-hard-ferrite:
    title: Hard ferrite magnets, product information (thyssenkrupp Materials Germany)
    id: thyssenkrupp Magnettechnik product information
    url: https://ucpcdn.thyssenkrupp.com/_binary/UCPthyssenkruppBAMXSchulteMicrositeMagnettechnik/en/downloads/link-thyssenkruppMagnettechnik-Factsheet-ferrite-magnets.pdf
    kind: datasheet
    license: manufacturer product information (cited, not reproduced)
  eclipse-ferrite-datasheet:
    title: Ferrite Magnets / Ceramic Magnets Datasheet (Eclipse Magnetics)
    id: Eclipse Magnetics ceramic magnets datasheet
    url: https://www.eclipsemagnetics.com/site/assets/files/19602/ferrite_ceramic_datasheet.pdf
    kind: datasheet
    license: manufacturer datasheet (cited, not reproduced)
  nist-atomic-weights:
    title: NIST Atomic Weights and Isotopic Compositions for All Elements (iron and oxygen rows)
    id: NIST Physical Measurement Laboratory, Compositions table
    url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=Fe&all=all&ascii=html
    year: 2024
    kind: database
    license: public domain (NIST)
license: CC-BY-4.0
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 30
  unreachable: 0
  caveats: 4
  note: Read by an AI assistant on 2026-10-26 from the pages and PDFs fetched in that run. The hard ferrite values are minimum values from one manufacturer. The hematite Néel temperature and Morin transition come from one arXiv paper. Samarium ferrite and bismuth ferrite were mentioned from one open paper each. The TDK catalogue is a 2013 print.
story:
  recipe:
    line: Iron oxides combine iron with oxygen. Hematite is Fe2O3, with iron in the three-plus state, in a corundum-type structure. Magnetite is Fe3O4, a cubic spinel with iron in two valence states. Strontium ferrite is SrO.6Fe2O3, an oxide in which strontium oxide is combined with six parts of iron oxide, and it forms a hexagonal structure.
    parts:
      - name: Iron
        symbol: Fe
        atoms: 2
        atomic_weight: 55.845
        role: The metal ion that carries the magnetism. In hematite and magnetite the iron ions order magnetically below their transition temperatures.
      - name: Oxygen
        symbol: O
        atoms: 3
        atomic_weight: 15.999
        role: Forms the oxide framework that holds the iron ions. In hematite there are three oxygen atoms for every two iron atoms.
  risk_groups:
    - title: For people
      level: 0
      verdict: Most reports say not hazardous; dust limits apply
      lead: Most company reports in PubChem say iron oxide does not meet GHS hazard criteria, but some notifications give eye, skin and respiratory hazards. The exposure limits for dust and fume are the practical concern.
      points:
        - label: The powder
          line: PubChem reports that 66.9% of company reports (2296 of 3433) do not meet GHS hazard criteria. Some notifications give H319 eye irritation (18.5% of reports) and H411 aquatic toxicity (12%).
        - label: Dust and fume
          line: The OSHA limit is 10 mg/m3 for iron oxide fume, and NIOSH gives 5 mg/m3 as Fe for dust and fume.
        - label: Long exposure
          line: Prolonged exposure to high levels of iron dust or fume (10 to 700 mg/m3) can cause siderosis, a benign lung condition.
    - title: If a magnet overheats
      level: 1
      verdict: Loses magnetism above its rated temperature
      lead: Ferrite magnets are rated to about 250 degC. Above that they lose remanence, and they can crack if handled roughly.
      points:
        - label: Rated limit
          line: The maximum operating temperature of hard ferrite magnets is 250 °C. The Eclipse Magnetics sheet allows up to 300 °C in a few situations.
        - label: Temperature effect
          line: Remanence falls by 0.2 % per kelvin as the magnet warms, and the coercive field rises by 0.3 to 0.4 %.
        - label: Brittleness
          line: Sintered ferrite is brittle, so sharp edges, corners and cuts across the pressing direction can crack the magnet.
    - title: Handling and storage
      verdict: Dust control and simple disposal
      points:
        - label: Dust
          line: Use a particulate filter respirator where dust is airborne, and sweep spills into covered containers.
        - label: Water and acids
          line: Ferrite magnets resist water and alkaline solutions, but concentrated mineral acids attack them.
        - label: Disposal
          line: The magnet maker says ferrite magnets are non-toxic in landfill and unaffected by incineration.
  why: 'Iron oxides are cheap, widely available and stable in air and water. Hematite is the red pigment oxide and is antiferromagnetic up to its Néel temperature. Magnetite is a ferrimagnet with a Curie temperature of 858 K. Ferrites carry this magnetism into engineering use: hard strontium hexaferrite is the main permanent magnet in motors and loudspeakers, and soft MnZn ferrite cores carry flux in power transformers. The trade is weaker magnetism per volume than NdFeB or SmCo magnets, in exchange for low cost and good chemical stability. Bismuth ferrite and samarium ferrite are related oxides with magnetic order at higher temperatures; only one source was read for each.'
  uses:
    - where: Magnet motors and loudspeakers
      line: Strontium hexaferrite is the most used permanent magnet family. One review puts it at 85 wt.% of the permanent magnet market, and ferrite magnets are used in motors, generators and loudspeakers.
    - where: Transformer cores
      line: MnZn ferrite grades such as N87 are sold for power transformers and work across an optimum frequency range of 25 to 500 kHz.
    - where: Pigments
      line: Iron oxide pigments colour paint, coatings, concrete and plastics. The USGS calls them colour stable, unlike many organic colourants that fade in sunlight.
    - where: On Mars
      line: Hematite is widely distributed across the surface of Mars. Hematite spherules, called blueberries, were found in Meridiani Planum by the Opportunity rover.
  can_do:
    - label: Magnetic order
      value: Néel 948 K
      line: Hematite stays weakly ferromagnetic up to about 948 K. Below its Morin transition, at 250 to 260 K, the spins reorient into a purely antiferromagnetic state.
    - label: Magnetite
      value: Curie 858 K
      line: Magnetite is ferrimagnetic below its Curie temperature of 858 K and undergoes the Verwey transition near 125 K.
    - label: Hard magnets
      value: 380 mT remanence
      line: Hard ferrite grade 28/26 has a minimum remanence of 380 mT, a minimum coercivity of 260 kA/m and a maximum energy product of 28 kJ/m3.
    - label: Soft cores
      value: 490 mT at 25 °C
      line: MnZn power ferrite N87 has a flux density of 490 mT at 25 °C and 390 mT at 100 °C, with a Curie temperature above 210 °C.
  compare: Iron oxides trade field strength for cost and stability. Ferrite magnets are the cheapest permanent magnets and do not rust in water, but they are weaker per size than NdFeB or SmCo magnets, according to the magnet maker Eclipse Magnetics. A hard ferrite grade at 380 mT remanence is therefore suited to motors and loudspeakers, not to high-field actuators. The table compares density, Curie temperature and remanence with the other oxides in this collection.
  compare_rows:
    - label: Density
      benchmark: density
    - label: Curie temperature
      benchmark: curie_temperature
    - label: Remanence
      benchmark: remanence
  handling:
    - Use a particulate filter respirator where iron oxide dust or fume is airborne.
    - Sweep spilled material into covered containers, and ventilate the area if fume is released.
    - Keep hard ferrite magnets below their rated maximum of 250 °C.
    - Avoid sharp edges and machining across the pressing direction, which cause cracks.
  good_for:
    - Cheap permanent magnets that do not rust in water, used in motors, generators and loudspeakers (Eclipse Magnetics).
    - Low-loss power transformer cores across an optimum range of 25 to 500 kHz (TDK N87).
    - Colour-stable pigments for paint, coatings and concrete (USGS).
  watch_out:
    - Weaker magnetism per size than NdFeB or SmCo magnets, and brittleness of sintered parts.
    - 'Magnetism falls as the magnet warms: remanence drops by 0.2 % per kelvin.'
    - Hazard data are mixed. Most PubChem company reports say not classified, but some give H315, H318, H335 and H372.
  verdict: Iron oxides are the low-cost, stable end of the magnetic materials. Their weak point is magnetic strength per volume, so they suit motors, loudspeakers and transformers better than high-field actuators.