AC SUSCEPTIBILITY OF A SPHERICAL ND2FE14B SINGLE-CRYSTAL

The external complex ac susceptibility chi(e) = chi(e)'-j-chi(e)" of a spherical Nd2Fe14B single crystal has been measured as a function of temperature, field amplitude, and frequency in both directions, parallel and perpendicular to the c axis. Chi(e)'(perpendicular-to) for T > T(s) the spin reorientation temperature, is due to domain-magnetization rotations (DMR's). Chi(e)'(perpendicular-to) for T < T(s) is due to comparable DMR's and domain-wall displacements (DWD's). Chi(e)'(parallel-to) for the whole range is mainly due to DWD's. DWD's are usually enhanced by DMR's. There is an anomalous sharp chi(e)'(parallel-to) peak at T = T(s) for low fields and frequencies, which is ascribed to a technical magnetization mechanism when the first anisotropy constant equals zero. For data analyses and explanation, relations between the low-field susceptibility and the anisotropy constants, expressions of the domain-wall energy density, and a formula for chi(e)" arising from eddy currents for a metallic magnetic sphere have been derived.