Ferromagnet or spin glass? Magnetic ordering in Au-Fe alloys

Abstract

Bulk magnetization measurements on Au-Fe alloys are widely held as indicating the onset of long range ferromagnetism in alloys with Fe concentration above about 12 at.%. The 'ordering' temperatures deduced from these measurements appear to be in reasonable agreement with temperatures of the maxima of d rho /dT in the resistivity of the alloys but are considerably higher than the values obtained from Mossbauer effect measurements for alloys in the concentration range between 12 and 20 at% Fe. Magnetization measurements on a Au-15at% Fe alloys are presented which, contrary to the above, show a behaviour usually associated with spin glass alloys and indicate a spin freezing temperature close to the 'ordering' temperature expected from Mossbauer effect measurements. The results show that the apparent ferromagnetic behaviour and higher ordering temperatures obtained by previous workers in their magnetization measurements have a simple physical explanation based on the intrinsic properties of the alloys.