Structural and magnetic properties of Ni2MnIn Heusler alloy films

By co-evaporation of Ni and an alloy of Mn and In, thin films of the Heusler alloy Ni2MnIn are deposited at temperatures around 300-bar C. Electron diffraction reveals the L21-ordered cubic structure (Fm3m). Magnetization data shows an onset of ferromagnetism at 318K in close agreement with previous results on bulk Ni2MnIn, while the saturation magnetization appears to be 15% below the bulk value. The field-dependent and the zero-field-cooled magnetizations indicate superparamagnetism, which can be related to the granular nanostructure of the films. A particle size of 23nm is extracted, which is in the order of the film thickness (39nm) and agrees with a mean grain size of (25+/-5)nm observed by transmission electron microscopy. The magnetic blocking at Tbl=280K is attributed to the strong dipole interaction between the grains