Thickness dependence of ferrimagnetic compensation in amorphous rare-earth transition-metal thin films

Magnetic compensation in ferrimagnets plays an important role in spintronic and magnetic recording devices. Experimental results have demonstrated a thickness dependence of the compensation temperature ( $T_{\text{comp}}$ ) in amorphous TbFeCo thin films. It was speculated that this thickness dependence originated from a variation in the short-range order. In this work, we have investigated the depth-resolved compositional and magnetization profiles using polarized neutron reflectometry. We find that although the composition is uniform across the film thickness, near the substrate interface, the magnetization exhibits a different temperature dependence from that of the rest of the sample. Monte Carlo simulations show that it is this difference in interfacial magnetization that causes the aforementioned thickness dependence of the compensation. These results demonstrate the critical role of the substrate interface in determining the magnetic properties of amorphous ferrimagnetic thin films for spintronic applications.