Dynamical susceptibility of Ho2Fe14B single crystal: Spin rotation and domain wall motions

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Abstract
The complex ac magnetic initial susceptibility (χ=χ’−jχ‘) has been measured along the [100], [110], and [001] directions from 4.2 to 300 K. Along the two basal directions the spin‐reorientation phase transition (SRT) is detected at TS =57.8 K as an abrupt steplike anomalous decrease in χ’ for increasing temperature. The value of the experimental ratio χ’[110]/ χ[100] ≂2 holds for T≥TS. The reversible magnetic moment rotation set on by the exciting ac magnetic field explains these results, allowing a fit from which the stress constant σ=42±1 kg/mm2 is derived. Along the [001] direction no anomaly in χ’(T) is detected at TS while a strong continuous increase is manifest above 150 K. It is explained by the onset of narrow wall motions between 180° domains induced by thermal excitations.