Temperature dependent approach-to-saturation in soft-magnetic particle assemblages: Separating work against stress and demagnetization

Micromagnetism historically started with the analysis of the approach-to-saturation (ATS) of hysteresis loops of ferromagnetic materials. For soft magnetic particulate samples the ATS behavior at varying temperatures depends strongly on magnetostatically controlled shape anisotropy. Scaling micromagnetic energies by demagnetizing energy, the scaled reversible work (SRW) due to demagnetizing energy becomes independent of temperature. Observed temperature variations in SRW can therefore be attributed to other micromagnetic energy terms which may be identified through the known temperature variations of magnetostriction and magnetocrystalline anisotropy constants. A detailed analysis of the temperature variation of SRW can therefore separate the energy contributions of magnetostatic interaction, internal stress, and magnetocrystalline anisotropy. For homogeneous magnetizations it is possible to calculate calibration curves to estimate stress in soft magnetic materials. Three-dimensional micromagnetic calculations provide a more detailed view of grain-size dependent mechanisms of SRW in soft magnetic materials like Ni, Co, Fe, and Fe 3 O 4 . • Temperature dependent approach-to-saturation separates stress and interaction effects. • A method to calculate calibration curves for soft-magnetic materials. • Three-dimensional micromagnetic calculations show that non-uniform magnetization contributes to SRW in magnetite.