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Abstract:
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 behaviour upon irradiation: they are nearly constant up to ion fluences of ≈6 × 1015 ion cm−2, while they decrease with further increasing fluences and finally vanish at a fluence of ≈9 × 1016 ion cm−2, when the sample becomes paramagnetic. However, contrary to this behaviour, the QMOKE signal nearly vanishes even for the smallest applied fluence of 3 × 1014 ion cm−2. 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.
