Frustration and long-range behavior of the exchange interactions in AuFe spin-glass alloys

We calculate the effective exchange pair interactions between Fe atoms in fcc Au-rich AuFe spin-glass alloys from first principles. The character of magnetic frustrations as well as the asymptotic behavior of the exchange interactions are strongly concentration dependent: the AuFe magnetic system becomes less frustrated as the Fe concentration increases since the antiferromagnetic interactions are stronger reduced than the ferromagnetic ones. It is also found that, as compared to the standard Rudermann-Kittel-Kasuya-Yosida (RKKY) theory, the distance dependence of the exchange interactions strongly varies with the Fe concentration. For example, for 5% of Fe we already find a pronounced exponential damping of the exchange interactions due to disorder, which in turn is in striking contrast to the well-known power-law decay predicted by ordinary RKKY.