More on the low-temperature magnetism of stable single domain magnetite: Reversibility and non-stoichiometry

The loss in remanence at the Verwey transition (T_v) was modeled for elongate stable single domain magnetite for two experiments: 1) thermal cycling of room temperature saturation isothermal remanent magnetization (RTSIRM), 300 → 10 → 300 K, and 2) warming of zerofield cooled and field-cooled remanences from 10 K to 300 K. The RTSIRM simulations used magnetocrystalline anisotropy constants for stoichiometric magnetite and aspect ratios (AR) from 1 to ∞, for assemblages of inorganic particles and 10-magnetosome chains. The results match the experimentally observed behavior of reversibility. The second set of simulations was conducted with low-temperature magnetocrystalline anisotropy constants for varying degrees of non-stoichiometry, and AR = 5. Minor non-stoichiometry lowers the drop in remanence at T_v and increases the "delta ratio" (δ_fc/δ_zfc) to values as high as ∼6. New experiments demonstrate that maghematization (non-stoichiometry) can partly explain the low-temperature magnetic behavior observed in magnetotactic magnetite to date.