Theory of magnetism in amorphous FeZr alloys

Abstract

Various magnetic properties of amorphous FeZr alloys have been investigated on the basis of the finite-temperature theory of amorphous magnetic alloys. The numerical results explain the overall features of the magnetization versus concentration curve and the magnetic phase diagram showing the spin glass, the ferromagnetism, and the paramagnetism, including the re-entrant spin-glass behavior in the Fe-rich region. It is verified by various analyses that the spin glass is caused by the nonlinear magnetic couplings and the fluctuations of the amplitudes of local moments due to structural disorder, while the ferromagnetism is stabilized by the decrease in the average coordination number of Fe atoms due to atomic size effects. Broad distributions of the local magnetic moments are found in both spin-glass and ferromagnetic states in the Fe-rich region. Their concentrations and temperature dependences are elucidated on the basis of the electronic structure and nonlinear magnetic couplings. Calculated high-field susceptibilities explain the anomaly around the re-entrant spin-glass region. Calculated effective Bohr magneton numbers predict a minimum around 35 at% Fe. The effects of atomic short-range order on the magnetic phase diagram are also investigated. It is found that the ferromagnetism disappears in the whole concentration when the probability of finding an Fe atom at the neighboring site of an Fe atom is larger than 0.8.