The effect of ion irradiation and annealing on exchange spring magnets

It is demonstrated that both the nucleation field and the irreversible switching field of Sm2Co7/Fe exchange spring bilayers is decreased by means of 10 keV He ion irradiation. The reduction is attributed to interfacial mixing and irradiation induced softening of the hard magnetic layer. By lowering the energy to 0.8 keV the ions do not penetrate the hard magnetic layer and consequently no softening is observed. However, although irradiation induced interfacial mixing is still present it is not large enough to create a graded interface layer and the nucleation field decreases. In contrast conventional annealing under appropriate conditions leads to an increase of the nucleation field. This distinct discrepancy can be explained by detailed investigation of the layer structure by x-ray reflectivity measurements.