Field-Cooled and Zero-Field-Cooled Magnetization of Superparamagnetic Fine Particles in Cu97Co3Alloy: Comparison with Spin-Glass Au96Fe4Alloy

The field-cooled (FCM) and zero-field-cooled (ZFCM) magnetization of ferromagnetic fine cobalt particles in a Cu 97 Co 3 alloy has been studied. The spin-glass-like temperature dependence of the magnetization has been observed; ZFCM exhibits a spin-glass-like maximum (at T p ) and FCM is larger than ZFCM at low temperatures. However, the difference between FCM and ZFCM obviously exists far above T p . Furthermore, FCM increases monotonically with decreasing temperature even below T p while that of typical spin glasses is nearly independent of temperature. The analysis of the magnetization shows that the temperature dependence of FCM and ZFCM of Cu 97 Co 3 is well described on the basis of the superparamagnetic blocking model with no interaction between the particles, whereas that of a typical spin-glass Au 96 Fe 4 cannot be explained by the blocking model.