The classic Stoner-Wohlfarth model for ferromagnetic particle aggregates is extended to the magnetization-vector (M) behavior of samples rotated in fixed magnetic fields (H). The predicted behavior depends critically on the size of H relative to HK, the effective anisotropy field of each constituent particle. For H≤HK, M has a rotational component MR, which turns synchronously with the sample, plus a component parallel to H, which grows with increasing H. For HK<;H<2HK, M turns initially until it reaches and remains (as MF) at a fixed frictional angle relative to H, while the sample continues to rotate; the frictional angle diminishes to zero at H = 2HK. This frictional behavior derives directly from the abrupt orientational changes of the particle magnetizations that occur over this range of H. Corresponding rotational M vector experiments were carried out on a sample disk cut from a commercial magnetic memory material. The results reveal a coexistence of rotational MR and frictional MF components, but MR is predominant at low H and MF becomes increasingly predominant at higher H. The gradual changes with H seen experimentally indicate a fairly broad distribution in the values of HK for the different particles. The average value of HK deduced from the rotational data agrees closely with the average value indicated by a measured hysteresis loop that also suggests that HK has a broad range of values.
- Ferromagnetic particle aggregates
- Frictional magnetic behavior
- Rotational magnetic properties
- Stoner-Wohlfarth model
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics