Magnetic Ordering in Gold-Iron Alloys

TLDR

The study aims to characterize magnetic ordering in AuFe alloys. This is achieved by measuring temperature‑dependent thermoelectric power and low‑field magnetic susceptibility across Fe concentrations of 1–22 at.%. Concentration‑dependent thermoelectric power and susceptibility data reveal that AuFe alloys transition from short‑range ferromagnetic order at higher temperatures to long‑range ferromagnetism for Fe concentrations above ~12 at.%, while lower concentrations exhibit well‑defined antiferromagnetic ordering with spin‑glass–like features, suggesting a more perfect antiferromagnetic state linked to local lattice arrangements.

Abstract

In an attempt to characterize the magnetic ordering in $\mathrm{Au}\mathrm{Fe}$ alloys, systematic studies were made of the temperature dependences of the thermoelectric power $S$ and the low-field magnetic susceptibility $\ensuremath{\chi}$ for Fe concentrations $C$ from 1 to 22 at.%. The concentration dependences of the magnitude and temperature of the maximum in $S(T)$ showed transitions clearly related to the magnetic ordering. Data analyses based on molecular field theories indicate the existence of small regions of short-range ferromagnetic order which undergo longrange interactions as the temperature is lowered. For $C\ensuremath{\gtrsim}12$ at.,% long-range ferromagnetism is dominant. Lower-concentration alloys ($C\ensuremath{\lesssim}12$ at.%) exhibit an antiferromagnetism with some properties similar to those of a magnetic spin-glass, but with well-defined ordering temperatures characterized by sharp cusps in $\ensuremath{\chi}(T)$, and with a negative Curie $\ensuremath{\theta}$ for $C=1 \mathrm{and} 2$ at.%. These properties indicate a more perfect antiferromagnetic order than that expected for a random alloy or a spin-glass, and this may be related to preferred local lattice arrangements in these alloys.