Stability of Anhysteretic Remanent Magnetization in Fine and Coarse Magnetite and Maghemite Particles

Abstract

Summary Further experiments have been performed to investigate the biasing-field dependency of alternating field demagnetization curves of anhysteretic remanent magnetization as a simple test for the domain state of magnetite and maghemite particles. The biasing-field dependency in fine-grained particles was opposite to that in coarse-grained particles. The experiments were conducted on well sized synthetic specimens in the single domain, pseudo-single domain and multi-domain grain size ranges. A single domain-like biasing-field dependency was observed in equidimensional particles up to 0.2,~ in mean grain size and up to 0.4~ in elongated grains. Either the single domain/pseudo-single domain boundary lies above at least 0.2~ grain size or this field dependency test does not distinguish between single domain and pseudo-single domain states. A multidomainlike trend was observed in very coarse magnetite. The test may possibly distinguish the change from pseudo-single domain to multi-domain states. If both fine and coarse fractions are present a confusing overlap of the demagnetization curves occurs.