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.