ANISOTROPY OF THE HIGH-FIELD MAGNETIZATION OF CUBIC ZN1-XFEXSE

The magnetization of cubic ${\mathrm{Zn}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Fe}}_{\mathit{x}}$Se, with x=0.003 and 0.007, was measured at temperatures 2\ensuremath{\le}T\ensuremath{\lesssim}50 K in magnetic fields H along the [100] and [111] directions. Data for H\ensuremath{\le}55 kOe were taken with a superconducting quantum interference device magnetometer. Other data in fields up to 200 kOe were taken with a vibrating sample magnetometer operating in a Bitter magnet. At the lowest temperatures the magnetization M at high magnetic fields is anisotropic: at a given T and for the same magnitude H of the magnetic field, M for H\ensuremath{\parallel}[100] is larger than for H\ensuremath{\parallel}[111]. The difference between the values of M for these directions reaches a maximum value of 19% at the lowest temperatures and when H\ensuremath{\simeq}150 kOe. As the temperature rises, the anisotropy of the high-field magnetization decreases gradually, becoming very small above 40 K. In low fields (H\ensuremath{\lesssim}10 kOe) the anisotropy is very small at all temperatures. These experimental results are generally in good agreement with theoretical calculations based on crystal field theory and on the assumption that only isolated ${\mathrm{Fe}}^{++}$ ions (singles) contribute to the magnetization. Minor discrepancies between experiment and theory remain, however.