Location and morphology of ferromagnetic precipitates in Ni-Mn-Sn

Ni50Mn45Sn05 heated above 600 K decomposes into ferromagnetic Ni2MnSn precipitates in an antiferromagnetic NiMn matrix. If an external magnetic field is applied during annealing, magnetic hysteresis curves with high coercive fields of up to 5 T can be achieved. The origin of this hysteresis has been attributed to the coupling of the antiferromagnetic matrix with the ferromagnetic precipitates, whose location and morphology were not known. To close this knowledge gap, four samples with varying annealing treatments were investigated using switching magnetization magnetic force microscopy. One sample was additionally analyzed with transmission electron microscopy and atom probe tomography. The decomposition type is identified to be a cellular precipitation starting at grain boundaries and growing into the grains. This leads to a multilayer thin film like lamellar structure with a lamella thickness in the nm range. Our results provide a basis for understanding the magnetic interactions, which lead to the magnetic hysteresis with ultra high coercivity.