Superlattice dislocations and magnetic transition in Pt3Fe alloy with the L12-type ordered structure

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Abstract
The magnetic susceptibility was measured in plastically deformed 25.6 at.% Fe-Pt single crystals. The susceptibility decreases considerably as a result of a small strain epsilon of 1.3% and at the same time spontaneous magnetisation appears. The spontaneous magnetisation increases with increasing plastic deformation. On cooling, the spontaneous magnetisation increases rapidly near the Neel temperatures and has a local maximum at 150 K. The dislocation density and its distribution were also observed by transmission electron microscopy. Superlattice dislocations are distributed making a pair. Near the anti-phase boundary between two superpartials, Fe atoms occupy the face-centred sites and couple ferromagnetically. The relation between the spontaneous magnetisation and the dislocation density is discussed using a simple localised moment model. It is shown that the ferromagnetic transition is extended as far as about twentieth nearest neighbour from the anti-phase boundary. The influence of the ferromagnetic clusters on their neighbouring Fe atoms is extended as far as 102 nm and the Fe atoms change to being superparamagnetic. This long-distance influence and the local maximum of spontaneous magnetisation should be explained from the viewpoint of the itinerant-electron model.