Room temperature ferromagnetism down to 10 nanometer Ni–Fe–Mo alloy films

Abstract

Magnetic behavior of a few pulsed laser deposited soft ferromagnetic thin films of Ni–Fe–Mo alloys of different thickness on sapphire single crystals is interpreted on the basis of their structural characteristics. Highly textured thin films have high void density due to island-like growth. X-ray reflectivity (XRR) of the thin films indicate that instead of a uniform density there are effectively three layers with density gradient across the thickness, which is further supported by atomic force microscopy and cross-sectional scanning electron microscopy. Rutherford backscattering spectroscopy and energy dispersive spectrum measurements reveal that the composition in the films is not too far from that of the bulk target with a trend of enhanced Fe yield in the films. The structural disorder strongly affected the magnetic property of the films resulting in much higher values of the Curie temperature TC and coercive field HC than those of the bulk targets. Bifurcations of low-field zero-field-cooled and field-cooled magnetization reflect the disorder-induced anisotropy in the thin films. The spin wave stiffness constants D are higher than their bulk counterparts which are supportive of the enhanced Fe yield in the films. The saturation magnetization, M calculated from measurements in field transverse to the films strongly supports the thickness found from XRR. Finally, even the 10nm thin films have sizable M and HC and TC >300K, making them good candidates for magnetic applications. Overall, the magnetic behavior and the structural characteristics have reasonably complemented each other.