A Co2FeSi (CFS) film with L21 structure was irradiated with different fluences of 30 keV Ga+ ions. Structural modifications were subsequently studied using the longitudinal (LMOKE) and quadratic (QMOKE) magneto-optical Kerr effect. Both the coercivity and the LMOKE amplitude were found to show a similar behavior upon irradiation: they are nearly constant up to ion fluences of ≈6×1015 ion/cm2, while they decrease with further increasing fluences and finally vanish at a fluence of ≈9×1016 ion/cm2, when the sample becomes paramagnetic. However, contrary to this behavior, the QMOKE signal nearly vanishes even for the smallest applied fluence of 3×1014 ion/cm2. We attribute this reduction of the QMOKE signal to an irradiation-induced degeneration of second or higher order spin-orbit coupling, which already happens at small fluences of 30 keV Ga+ ions. On the other hand, the reduction of coercivity and LMOKE signal with high ion fluences is probably caused by a reduction of the exchange interaction within the film material.
@article{arxiv.cond-mat/0609633,
title = {Ion beam induced modification of exchange interaction and spin-orbit coupling in the Co$_2$FeSi Heusler compound},
author = {J. Hamrle and S. Blomeier and O. Gaier and B. Hillebrands and H. Schneider and G. Jakob and B. Reuscher and A. Brodyanski and M. Kopnarski and K. Postava and C. Felser},
journal= {arXiv preprint arXiv:cond-mat/0609633},
year = {2015}
}