Invariance of the magnetization axis under spin reorientation transitions in polycrystalline magnets of Nd2Fe14B

A great number of useful and practical devices benefit from the use of Nd2Fe14B magnets because of their good magnetic properties and relatively low cost. However, Nd2Fe14B presents a spin-reorientation transition (SRT) at cryogenic temperature that constitutes a challenge for engineers aiming to design devices for use in this environment. Although the spin reorientation transition is well-known for single crystals, there are very few papers describing experiments with polycrystalline samples. In this paper we show the effects of the SRT in macroscopic commercial samples, providing useful experimental data for designers. It has been proven that the macroscopic axis of magnetization in polycrystalline magnets of Nd2Fe14B remains invariant under spin reorientation transition whenever it occurs at H = 0 T. However, the transverse magnetic susceptibility slightly increases after the spin reorientation transition. This makes Nd2Fe14B suitable for cryogenic applications in which permanent magnets with defined axis of magnetization are required. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4754445]