Magnetic order in Metamagnetic Shape Memory Alloys: a muon study

Metamagnetic Shape Memory Alloys (MMSMAS) undergo a martensitic transformation which is accompanied with a large drop in magnetization on cooling, making the low temperature phase (martensite) either weakly magnetic or non magnetic at all, in stark contrast and contrary to the conventional behaviour of magnetic materials. Such behaviour enables the achievement of the reverse transformation into austenite by application of a moderate magnetic field. The ferrimagnetism of the austenitic phase is well documented. However, the magnetic character of the martensitic phase remains controversial and different behaviours, such as a spin glass phase, antiferromagnetic or just a paramagnetic phase have been suggested. We propose to carry out a muon spin rotation and relaxation study on the Ni42Co8Mn39Sn11 MMSM alloy to discriminate the presence of spin-glass or weak antiferromagnetic phases.