High-temperature techniques for measuring microcoercivity, crystallite size, and domain state

摘要: We describe three useful techniques for investigating magnetic microstructure and granulometry, high-temperature alternating-field (AF) demagnetization, thermal fluctuation analysis (TFA), determination of the demagnetizing factor N, give examples their use. For synthetic magnetite samples, thennoremanent magnetization anhysteretic remanent are shown to differ in AF demagnetization spectra at all temperatures up blocking range. Moreover, various coercivity fractions either spectrum evolve differently with temperature than does bulk coercive force. TFA force data dispersed crystals mean sizes 215, 390 540 run indicate that ≈200 nm regions thermally activated each case. These may be responsible pseudo-single-domain behaviour. A crude estimate N multidomain grains any is ratio between saturation remanence. The 215–540 magnetites appear contain two or domains −100°C 400°C; new nucleate higher temperatures.