Detecting an in-plane rotation of magnetization in GdFeCo films

It is often important to distinguish between magnetization reversal by coherent rotation in different planes and domain wall motion. Magnetization curves were measured at different temperatures with magneto-optical Kerr Effect in longitudinal (L-MOKE) and polar (P-MOKE) geometries on sputter-deposited Gd$_{\mathrm{x}}$Fe$_{\mathrm{y}}$Co$_{\mathrm{1-x-y\thinspace }}$(GFC) films of variable thickness. Depending on the probed region, the L-MOKE signal measured with decreasing external field H$_{\mathrm{ext}}$ was found to be lower than the signal observed with increasing H$_{\mathrm{ext}}$ (negative remanence magnetization). We show that this is due to a contribution to the signal of$\thinspace M_{\bot }$, the magnetization component perpendicular to the scattering plane. This identifies the type of reversal in these GFC films as in-plane coherent rotation of magnetization. $M_{\bot }$ is also proportional to the torque. Azimuthal measurements on Co$_{\mathrm{2}}$FeAl samples showed a regular variation of the MOKE signal, in one possible application of these observations to torque measurements.