Comparison of magnetic methods for the determination of texture of permanent magnets

Abstract

The singular point detection (SPD) technique as well as a least‐mean‐square procedure of fitting trial texture functions to demagnetization curves (DMC) were applied in order to determine the orientation density of the tetragonal axes of the Nd2Fe14B crystallites in sintered Nd‐Fe‐B magnets with different degrees of grain alignment. Both methods are less complicated than calculating the texture function from x‐ray‐diffraction data. The orientation densities obtained by both methods agree fairly. Analytically, they can be described as a Gaussian or a sum of cosine‐power functions of the angle between the local tetragonal axis and the texture axis. This agreement is a test for the DMC method which can also be used for materials showing much larger anisotropy fields than the maximum available measuring field. The SPD and DMC methods can also be applied to measure the temperature dependence of the anisotropy field H A of the magnetic main phase in noncompletely textured polycrystallinematerials. By means of the DMC method additionally the spontaneous polarization J s as well as the anisotropy constants K 1 and K 2 can be determined. As expected, the values of H A of our sintered Nd‐Fe‐B samples, measured up to 140 °C, are nearly independent of the degree of texture and are in agreement with those reported in literature. This confirms that SPD as well as DMC can be used to measure intrinsic magnetic properties for materials which can hardly be prepared as single crystals, such as interstitial compounds made by gas–solid reactions.