Properties | Magnetite | Maghemite | Hematite |
---|---|---|---|
Molecular formula | Fe3O4 | γ-Fe2O3 | α-Fe2O3 |
Density (g/cm3) | 5.18 | 4.87 | 5.26 |
Melting point (°C) | 1583-1597 | – | 1350 |
Hardness | 5.5 | 5 | 6.5 |
Type of magnetism | Ferrimagnetic | Ferrimagnetic | Weakly ferromagnetic or antiferromagnetic |
Curie temperature (K) | 850 | 820–986 | 956 |
The saturation magnetization (Ms) at 300 K (A-m2/kg) | 92–100 | 60–80 | 0.3 |
Standard free energy of formation ΔGof (kJ/mol) | − 1012.6 | − 711.1 | − 742.7 |
Crystallographic system | Cubic | Cubic or tetragonal | Rhombohedral, hexagonal |
Structure type | Inverse spinel | Defect spinel | Corundum |
Space group | Fd3Â m | P4332 (Cubic), P41212 (tetragonal) | R3c (hexagonal) |
Lattice parameter (nm) | a = 0.8396 | a = 0.83474 (cubic); a = 0.8347, c = 2.501 (tetragonal) | a = 0.5034, c = 1.375 (hexagonal) aRh = 0.5427, α = 55.3o (rhombohedral) |