High temperature superparamagnetism in boron substituted FeZrMn alloys

In this paper, Fe₈₂Mn_8-xB_xZr₁₀ alloys, which evidences the existence of superparamagnetic state at high temperatures, is investigated. Curie temperature (T_C) is determined by an extrapolation of magnetization to zero value at its temperature dependence and equals to 302 K and 368 K for x=6 and x=8 samples, respectively. For x=6 samples, as the temperature increased, the electron magnetic resonance (EMR) spectra measured show at least two distinct lines. An existence of low field resonance at high temperatures and invariability of resonance field H_r1 indicate that this resonance line is caused by the paramagnetic state of amorphous matrix. Position of high field peak H_r2, shifted to higher field with temperature evidencing existence of the superparamagnetic state of nanoparticles embedded into the amorphous matrix. Magnetization of the nanoparticles decreased with temperature causing the increase of H_r2. Similar behavior is observed for x=8 samples only that the superparamagnetic clusters are observed in larger temperature interval above T_C. These experimental results are in agreement with the infinite three-dimensional FM matrix plus finite FM spin cluster model.