Europhys. Lett.
Volume 70, Number 4, May 2005
Page(s) 520 - 526
Section Condensed matter: electronic structure, electrical, magnetic, and optical properties
Published online 27 April 2005
Europhys. Lett., 70 (4), pp. 520-526 (2005)
DOI: 10.1209/epl/i2005-10013-7

The exchange coupling of dilute $\chem{Fe}$ and $\chem{Cr}$ in $\chem{Au}$Cr alloys: Formation of local magnetic clusters

O. Beutler1, 2, R. Kirsch1, 2, M. J. Prandolini1, 2, W. D. Brewer1, J. Kapoor2, P. J. Jensen1, S. Frota-Pessôa3 and D. Riegel2

1  Fachbereich Physik, Freie Universität Berlin - 14195 Berlin, Germany
2  Hahn-Meitner-Institut Berlin GmbH - 14109 Berlin, Germany
3  Instituto de Física da USP - CP 66318, 05315-970 São Paulo, S.P., Brazil

received 3 January 2005; accepted in final form 29 March 2005
published online 27 April 2005

We have used the atomic specificity and sensitivity of the in-beam perturbed $\gamma$-ray angular distribution method to investigate the magnetic behaviour of very dilute $\chem{{}^{54}Fe}$ implanted into $\chem{Au}$1-x$\chem{Cr}$x spin-glass alloys. Distinct magnetic responses due to the different configurations of $\chem{Au}$ and $\chem{Cr}$ nearest neighbours were observed. A single $\chem{Cr}$ nearest neighbour results in a notable decrease of the magnitude and reversal of the sign of the Curie constant of the paramagnetic implanted $\chem{Fe}$. We interpret this as the result of strong antiferromagnetic coupling between adjacent $\chem{Fe}$ and $\chem{Cr}$ local moments, leading to the formation of a local magnetic cluster, which remains stable up to the highest temperatures of the measurements (400$\un{K}$). A heuristic model using as input data the results of ab initio calculations of coupling constants, magnetic moments and hyperfine fields strongly supports this interpretation.

75.20.Hr - Local moment in compounds and alloys; Kondo effect, valence fluctuations, heavy fermions.
71.15.Mb - Density functional theory, local density approximation, gradient and other corrections.
76.80.+y - Mössbauer effect; other $\gamma$-ray spectroscopy.

© EDP Sciences 2005