Spin-glass and double-transition behavior in Gd-La glasses

We report studies of high-field magnetization, field-cooled magnetization, thermoremanent magnetization, and isothermal remanent magnetization as a function of temperature in the metallic glass sytem Gd_xLa _72-xG₂₈ where G₂₈=Ga ₁₈B₁₀ for the compositions x=72, 68, 64. The first two compositions show double-transition behavior and the last one shows only a paramagnetic to spin-glass transition. The approach to saturation at intermediate fields (up to 40 kOe) is of the form 1/H^{1 /2} as predicted by a mean field model which incorporates a small random anisotropy. The field-cooled magnetization in these samples is independent of time and is reversible, suggesting it is the equilibrium magnetization. This field-cooled magnetization in the double transition samples (and spin-glass sample) goes smoothly to zero with applied field, indicating the absence of an equilibrium macroscopic moment in zero applied field. The thermoremanence shows a maximum which becomes progressively more pronounced as x decreases.