The use of magnetic insulators is attracting a lot of interest due to the rich variety of spin-dependent phenomena with potential applications for spintronic devices. Here, we report ultrathin yttrium iron garnet (YIG)/gadolinium iron garnet ($\mathrm{Gd}\mathrm{IG}$) insulating bilayers on gadolinium gallium garnet (GGG). From spin Hall magnetoresistance (SMR) and x-ray magnetic circular dichroism measurements, we show that the YIG and $\mathrm{Gd}\mathrm{IG}$ magnetically couple antiparallel even in moderate in-plane magnetic fields. The results demonstrate an all-insulating equivalent of a synthetic antiferromagnet in a garnet-based thin film heterostructure and could open venues for insulators in magnetic devices. As an example, we demonstrate a memory element with orthogonal magnetization switching that can be read by SMR.

• Received 14 March 2018
• Revised 24 July 2018

DOI:https://doi.org/10.1103/PhysRevApplied.10.044046