Abstract
We report the magnetic properties for dispersed, spherical Fe3O4 and γ-Fe2O3 particles ∼ 250 nm in diameter in the temperature range T = 4.2–294 K. For Fe3O4, hysteresis properties show anomalies at 130 K, where the magnetocrystalline anisotropy constant K1 vanishes; the ratio Hc/Is (Hc = coercive force, Is = saturation magnetization) follows a linear relationship with K1/Is2 between 130 and 294 K. Below the Verwey transition temperature TV (∼ 120 K, the hysteresis properties depend on whether the sample is cooled in a strong magnetic field or in zero field; no magnetic anomalies were observed for γ-Fe2O3 particles, generated by oxidizing the Fe3O4 particles under study. The rotational hysteresis integral at 294 K is ∼ 0.7 for both compounds, pointing to a coherent-type magnetization reversal for assumed uniaxial single-domain particles (SDPs); however, the reduced saturation remanence is only ∼ 0.2, far below that for SDPs. Possible models for the particle magnetization modes are discussed.
Published Version
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