Amorphous metastable alloy of nominal composition ${\left({\text{Fe}}_{0.5}{\text{Cu}}_{0.5}\right)}_{87}{\text{Zr}}_{13}$ has been synthesized by high-energy ball milling. The alloy exhibit a ferromagnetic behavior with a Curie Temperature of $T_{\text{C}}=255\text{K}$, as determined from low-field measurements whereas no transition to a paramagnetic state is observed under high-enough applied magnetic fields. The evolution of hysteresis loops with temperature as well as thermoremanence measurements indicate an anomalous magnetic behavior characterized by a spontaneous increase in the magnetization values as well as by a magnetic hardening when the temperature is increased above $T_{\text{C}}$. These effects are strongly correlated with a dilation of the Fe-Fe nearest-neighbor distances, as determined from extended x-ray absorption fine structure (EXAFS) studies. EXAFS results indicate an almost negligible thermal expansion at temperatures below $T_{\text{C}}$ while normal thermal expansion takes place at higher temperatures. Such expansion seems to promote a reinforcement of the ferromagnetic interactions among Fe-Fe atoms that would account for the observed spontaneous increase in the magnetization as well as for the evolution of the coercive field.

• Received 18 March 2010

DOI:https://doi.org/10.1103/PhysRevB.82.012406