Magnon transfer torque in all insulating spin valve

Spin valves (SV), consisting of two metallic ferromagnetic layers separated by a non-magnetic layer, are essential building blocks for spin-based electronic devices. The information encoded in SV can be read and written by the giant magnetoresistance effect and the spin transfer torque. The physical mechanism underlying is the angular momentum exchange enabled by conduction electrons propagating across two magnetic layers. Here, we propose an all-insulating spin valve (ISV) structure made of an antiferromagnetic insulator sandwiched by ferromagnetic insulator (FI) layers. The incoherent magnons in the magnetic layers serve as angular momentum carriers and are responsible for the angular momentum transport. We predict two spin transport phenomena in the presence of temperature gradient: (1) a giant magneto spin-Seebeck effect in which the output spin current is controlled by the relative orientation of the two FI layers ,and (2) a magnon transfer torque that can be used for switching the magnetization of the FI layers with temperature gradient of the order of only 0.1 K/nm. The ISV provides a novel route to read and write magnetic information without the Joule heating compared to the conventional metal-based spin valve devices.