Structure Sensitivity of Magnetization Processes at the Spin-Reorientation Transition in Nd sub 2 Fe sub 14 B

Calculations based on different micromagnetic models were carried out to describe the behavior of the ac susceptibility in the temperature range of the spin-reorientation transitions in hard magnets (e.g. Nd sub 2 Fe sub 14 B). It was found that the rotational susceptibility shows a sharp cusp at the transition temperature, while the contribution due to an increase in the domain-wall mobility is less significant. Also, there is a significant contribution of domain-wall processes to the overall susceptibility over the entire range of temperatures studied (80-180K). For randomly oriented bulk samples, the susceptibility cusp has been experimentally observed. The susceptibility of randomly oriented powders shows only a moderate temperature dependence below the transition, followed by a sharp decrease at the transition temperature. The frequency dependence of the susceptibility showed the behavior expected for conducting samples, proving that domain-wall dynamics (e.g. aftereffects, lattice-defect--domain-wall interactions, etc.) do not play a role in the observed temperature dependence of the susceptibility.