Depending on a deposition method and post-deposition annealing, the magnetic properties of Ni-Mn-Ga films can vary substantially. Even in the well annealed films the influence of the martensitic transformation ­- the most characteristic feature of Ni­-Mn­-Ga ­- on their magnetic properties is either very small or is substantial.

The aim of this contribution is to elucidate the origin of these contradictions having a large number of experimental results on the sputtered and flash­-deposited Ni­-Mn­-Ga films of various compositions ( Ni_xMn_yGa_z) and Ni₅₀Mn₂₅Ga_25-xGe_x films heat-treated at various temperatures (from 620 - 973 K). The magnetic properties were investigated with ferromagnetic resonance in a wide temperature range and are compared with electric resistivity data. We show that the anomalous magnetic behavior of the Ni-Mn-Ga films annealed at T<800 K results from their columnar microstructure (which determines the effective shape anisotropy of these nominally heterogeneous films) and changes in the magnetic anisotropy due to the martensitic transformation. The films annealed at the highest temperatures reveal the magnetic behavior typical of normal ferromagnetic films, in which the effect of the martensitic transformation is strongly reduced due to constraint of a substrate. Ge substitution of Ga in Ni-Mn-Ga-Ge films has a detrimental effect on the martensitic transformation.

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