High-temperature superparamagnetism in boron substituted Fe-Zr-Mn alloys

A magnetization and electron spin resonance study of amorphous Fe₈₂Mn_8-xB_xZr₁₀ (x=6,8) ribbons is presented and discussed. Curie temperature of an amorphous matrix increased with x and equaled 302 K and 368 K for x=6 and x=8 alloys, respectively. A single resonance peak in ferromagnetic resonance (FMR) spectra was observed below Curie temperature, T_C, and at least two distinct resonance lines were well observed at temperatures higher than T_C. The low and high field-resonance lines were attributed to the paramagnetic state of the amorphous matrix and superparamagnetic states of nanoparticles embedded into the matrix, respectively. These observations could be qualitatively understood in terms of a finite-spin cluster plus an infinite ferromagnetic matrix model.