Magnetic Ordering in Gold-Iron Alloys

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 $\chi$ for Fe concentrations $C$ from 1 to 22 at.%. The concentration dependences of the magnitude and temperature of the maximum in $S\left(T\right)\mathrm{}$ 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 $C\gtrsim 12$ at.%, long-range ferromagnetism is dominant. Lower-concentration alloys ($C\lesssim 12$ 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 $\chi \mathrm{}\left(T\right)\mathrm{}$, and with a negative Curie $\theta$ for $C=1\mathrm{} \mathrm{and} 2$ 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.