Dependence of Ferromagnetic Resonance Behaviour on Chemical Disorder in Fe60Al40 Thin Films

We report on the influence of chemical disorder in Fe60Al40 thin films on their ferromagnetic resonance. Chemical disorder leads to increased nearest neighbour Fe-Fe magnetic interactions and plays a crucial role in inducing ferromagnetism. The saturation magnetization increases from 20 kA/m-1 for the chemically ordered film to 780 kA/m for disordered films. Disorder was induced by irradiation of Ne+ ions, and the depth-distribution of disorder was controlled by adjusting the ion-energy and -fluence. For moments aligned within the film plane, the resonant linewidth decreases with increasing ion-energy in the range from 2.5 to 30 keV, for a fixed ion-fluence. In-plane magnetic anisotropy is negligible in all cases. The linewidths for in-plane moment alignment are much larger than in materials that do not exhibit disorder induced ferromagnetism. These results may be explained by enhanced two-magnon scattering due to the presence of random defects, and help in preparing thin films with tailored spin-wave dynamic properties.