Metastability threshold sizes in single‐domain magnetite particles

A micromagnetic model was developed to calculate the maximum grain size for which an ideal parallelepiped‐shaped particle can have a metastable single‐domain (SD) structure. For mathematical tractability, the micromagnetic equations were described only by one‐dimensional deviations from a uniform SD state. It was found that for cubic‐shaped magnetite particles, the metastability threshold, a cr was approximately 0.14 micrometers, well above the equilibrium threshold size for the single‐domain to two‐domain transition. The metastability threshold size also increased rapidly with particle elongation and for a length:width ratio greater then 2.6, magnetite grains of all sizes could theoretically support a metastable single‐domain state.