Linear and non-linear magnetic response of potentially re-entrant Fe-Zr glasses

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Abstract
Detailed measurements are presented of the field and temperature dependent AC susceptibility of a number of FeZr metallic glasses. By following the behaviour of the 'cross-over' line, the presence of a paramagnetic to ferromagnetic transition below room temperature in this system is confirmed; the asymptotic exponent values characterizing this transition display near Heisenberg-like values (for the index delta , measurements extend to much lower fields than previous studies), although complications arising from anisotropy (most probably spin-orbit coupling) are also revealed. For the first time, the leading term in the non-linear response is shown to display a distinct anomaly at low temperatures. Although not divergent (as in Ising model predictions) the temperature at which this anomaly occurs in the 8 at.% Zr sample agrees with the transverse spin-freezing temperature estimated recently from in-field Mossbauer measurements. While detailed realistic three-dimensional model predictions describing sequential phase transitions in systems with competing exchange interactions are currently unavailable, the present data, nevertheless, support the possibility of a second 're-entrant' transition in this system.