Theoretical consideration of the stability of an L1₀ magnetic phase in Fe–(Pd, Pt) alloy clusters

Abstract

Size effects on the order–disorder transition of binary alloy clusters, particularly Fe–(Pd, Pt) clusters, are studied theoretically, based on the theory of Bragg and Williams. Including the broken bonds at surfaces (interfaces) of the clusters, the relationship between the degree of order and the cluster size, which has recently been suggested from various experimental studies, is formulated. The dependences of the critical size on the temperature and the order–disorder transformation temperature on the cluster size are derived. There is a slight quantitative disagreement with experiment, but this may be improved by considering some modification of higher-order terms.

Acknowledgements

The present authors would like to thank Professor H. Mori of Osaka University, Professor T. Mohri of Hokkaido University, Dr. M. Kohyama of the National Institute of Advanced Industrial Science and Technology (NIAIST) and Professor H. Orihara of Nagoya University for illuminating discussions. The present study is partly supported by a Special Coordination Fund for Promoting Science and Technology on Nano-Hetero Metallic Materials and grant-in-aid for the priority area ‘Localized Quantum Structure’ (No. 751) from the Ministry of Education, Science, Sport and Culture, Japan.