Origin of the anomalous contributions to the ac magnetic susceptibility of rare-earth–iron intermetallic compounds

Abstract

A systematic ac magnetic susceptibility, ac ͑T͒, study has been performed on several R 2 Fe 14 BH x ͑R = rare earth͒ compounds in order to determine the origin of the anomalous behavior of ac ͑T͒ not related to spin reorientation transitions-the so-called non-SRT anomalies. All the measurements have been performed on magnetically oriented samples to identify the anomalies due to domain-wall displacements. Different types of non-SRT anomalies have been found. It has been found that the anomalous behavior is mainly due to the existence of mobile defects coupled to the domain walls, which existence has been confirmed by performing magnetic aftereffect measurements. However, this mechanism alone cannot explain the whole phenomenology and other influences on ac ͑T͒ have to be taken into account to correctly describe the non-SRT anomalies. Specifically, three situations are possible when analyzing the anomalous behavior of ac ͑T͒: ͑1͒ compounds with no magnetic R anisotropy, in which the non-SRT anomalies are due to the existence of one or more mobile defects coupled to the domain walls, ͑2͒ compounds in which a large magnetic R anisotropy can influence the domain-wall mobility at very low temperatures, and ͑3͒ compounds in which a large magnetic R anisotropy and the existence of SRTs can influence the response of the domain walls coupled to mobile defects. Different fitting models have been proposed for each case.

Dynamics of AC susceptibility and coercivity behavior in nanocrystalline TbAl1.5Fe0.5 alloys

“…In Sm 2 Fe 3 alloy, an anomalous rise in the real component (w 0 ) is explained by dynamic domain-wall pinning and depinning, and as a consequence of thermally activated local directional ordering of Fe atoms [6]. Systematic magnetic AC-susceptibility (w ac ) measurements on several Re 2 Fe 14 BH x compounds have revealed the existence of mobile defects coupled to the domain walls [7]. From these works, it turns out that the analysis of AC-susceptibility dynamics is important to accomplish a more complete characterization of the magnetic behavior of these systems.…”

Stimulated spin noise in an activated crystal

“…The measurements of low-frequency AC susceptibility that have been started and primarily developed by C. Gorter 1 were mainly performed in the range of low magnetic fields (down to zero) and were aimed at studying the spin-spin interactions and the relaxationcontrolled response of the system. At present, the measurements of the 'nonresonant' magnetic susceptibility are widely used for studying diverse magnetic systems, alloys, superconductors, and minerals [2][3][4][5][6][7] .…”