Gyroremanent magnetization in magnetic tape and in iron and iron-alloy particles

Rotational remanent magnetization (RRM) and rotational anhysteretic remanent magnetization (ARM) have been produced in iron and iron alloys by rotating the samples in a slowly decreasing alternating field (80 mT initial peak). Coarse multidomain iron grains, and excarbonyl iron consisting of 1-9- mu m spheres, exhibited negligible RRM but a large ARM. Samples of metallic tape and Alnico permanent magnet alloys (Alcomax and Hycomax III), all of which consist of fine elongated particles, acquired a large RRM, which for a rotation frequency near twice the AF frequency (50 Hz) was comparable to or greater than an ARM produced under identical conditions (in a steady field of 44 mu T). The results are consistent with the gyromagnetic hypothesis of RRM acquisition in single-domain grains and also with previous results for magnetite.