Tailoring Ferrimagnetic Properties Using Proximity Effects in Co/Tb‐Co Bilayers

Abstract The presence of two magnetic sublattices in ferrimagnetic rare‐earth‐transition metal alloys enables the tuning of their magnetic properties by adjusting the film composition (e.g., magnetization, coercivity, as well as compensation and Curie temperatures). Using both experimental techniques and atomistic simulations, the magnetic properties of Co/(Tb‐Co) bilayers are studied across a broad range of parameters, including the thicknesses of the two layers and the composition of the alloy layer. This work demonstrates the ability to precisely modify the compensation point of Tb‐Co alloy thin films by adding a Co underlayer with a specified thickness. Furthermore, the range of parameters are identified for which the magnetization reversal of the alloy and Co layers occurs synchronously and provides a simple expression for calculating the effective composition of the bilayer system. Additionally, it is shown that an exchange‐spring magnet behavior can emerge when the alloy is Tb‐dominant and the Co underlayer thickness exceeds a critical threshold. It is also demonstrated that for Tb concentrations where the alloy layer is expected to be paramagnetic, the exchange coupling with the Co layer locally induces ferrimagnetic order near the interface, leading to a second transition back to Co dominance.