Rotational magnetic properties of Ni-Mn and Au-Fe spin-glass alloys

Magnetization-vector measurements were performed on field-cooled polycrystalline disks of Ni75Mn25 and Au85Fe15 rotated in a stationary field H. For Ni75Mn25 at 4.2 and 10 K, it is found that the induced anisotropy, which rotates rigidly with the sample for all H, is predominantly unidirectional but with uniaxial and higher-order components that are not negligible. Moreover, the rotational magnetization Mp/rrot is seen to be a unique function of the total effective field Hi/reff composed vectorially of H plus the anisotropy field HK, where M /rrot extends from its saturation value down to zero at Hd/reff=0. For Ni75Mn25 at higher temperatures, it is found that for H above a threshold value the direction of HK changes relative to the rotating sample. This phenomenon is also observed in Au85Fe15 at 4.2 K, and the directional changes of HK are seen to be a dissipative process, which is macroscopically frictional. Qualitative comparisons are made with the available theory.