Metallic magnetism from crystals to amorphous structures in Fe, Co, and Ni

Abstract

A theory of metallic magnetism that interpolates between crystals and amorphous structure has been developed on the basis of the functional integral technique and the distribution function method to investigate nonunique magnetism in amorphous Fe, Co, and Ni with different degree of structural disorder. Numerical results of various magnetic moments, susceptibilities, and magnetic phase diagram are presented as a function of the fluctuation of interatomic distance $[(\ensuremath{\delta}{R)}^{2}{]}_{s}^{1/2}/[R{]}_{s},$ the average coordination number ${z}^{*},$ and temperature. (Here $[{]}_{s}$ denotes the structural average.) It is demonstrated that there is a phase transition from the ferromagnetism to the spin glass in Fe with increasing structural disorder. The experimental data of amorphous Fe showing the ferromagnetism (the spin glass) are explained by the parameters ${z}^{*}\ensuremath{\approx}10.5$ ${(z}^{*}\ensuremath{\approx}11.5)$ and $[(\ensuremath{\delta}{R)}^{2}{]}_{s}^{1/2}/[R{]}_{s}\ensuremath{\approx}0.07.$ The Curie temperature ${(T}_{C})$ in Co is shown to increase monotonically with increasing the degree of structural disorder, but to have no maximum between the crystals and amorphous structure, while in Ni, ${T}_{C}$ decreases with increasing degree of structural disorder. The latter explains various ${T}_{C}$ as found by an extrapolation of the experimental data in Ni-rich amorphous alloys.