Tuneable, Rare-Earth Free, Synthetic Ferrimagnets for Optical Switching*

Synthetic ferrimagnets (SFM) are of particular interest as feasible media for all optical magnetic switching (AOS) [1]. SFM design requires knowledge and control of the magnetisation, M(T), and anisotropy, K(T), of each ferromagnetic layer, and the exchange coupling between them, J_ij(T). We have shown it is possible to engineer the magnetic properties of a series of compensating Ni₃Pt/Ir/Co SFM exhibiting perpendicular magnetic anisotropy (PMA). The tuneability of this structure provides an ideal system to investigate the effect of M(T), K(T) and J_ij(T) on reversal mechanisms within SFM, with distinct magnetic species allowing for element and layer specific characterisation. Initial pump/probe experiments reveal that it is possible to switch these SFM by application of optical laser pulses under a small applied field. AOS likely requires stronger antiferromagnetic exchange coupling than can currently be achieved in Ni₃Pt/Ir/Co SFM. A solution is to replace Ni₃Pt with a Ni/Pt multilayer, improving exchange coupling, maintaining element specificity, PMA and tuneability. [1] Nature Mat. 13, 286 (2014)