Spin-glass behaviour, thermal expansion anomaly and spin fluctuations in Y₂₀(Mn_1-xFe_x)₈₀ amorphous alloys

The spin-glass behaviour and the thermal expansion anomaly in annealed Y₂₀(Mn_1-xFe_x)₈₀ amorphous alloys have been investigated. The spin freezing temperature T_g shows a minimum at around x = 0.50, consistent with the theoretical investigation. The sign of the paramagnetic Curie temperature θ_p indicates that the average exchange interaction is antiferromagnetic in the Mn-rich concentration region and gradually becomes ferromagnetic with increasing x. The minimum of T_g occurs at the concentration where the sign of θ_p changes. The spontaneous volume magnetostriction is negligibly small in the Mn-rich concentration region and becomes larger with increasing x. These results are explained by the change in the spin fluctuation characteristics. In the Fe-rich concentration region, the thermal expansion anomaly takes place even in the paramagnetic temperature range due to the single-site spin fluctuation.