Exotic coupling in garnet-ferromagnet heterostructures

Metallic and insulating ferromagnets (FM) have been extensively studied for use in spintronic like structures—the former for spin transfer and spin orbit torques and the latter for generation of magnon spin currents [1,2]. Recently, we have shown that in yttrium iron garnet (YIG)/permalloy (Py) bilayers, grown on Si, the YIG preferentially aligns antiparallel to the Py at low field and can be used to form a magnon spin valve [3]. However, the observed coupling in YIG/FM is quite complex and is heavily dependent on the sample geometry—for example when the same bilayers are grown on Gd₃Ga₅O₁₂ (GGG) substrates, no antiparallel coupling has been observed. In this work, we discuss the coupling of YIG to Py and Co when grown on Si and GGG substrates by measuring the magnetic depth profile using polarized neutron reflectometry. The effect of texture and choice of FM on coupling to the underlying YIG layer will be presented in detail.

[1] S. Klingler, et al., Phys. Rev. Lett. 120, 127201 (2018).
[2] H. Wu, et al., Phys. Rev. Lett. 120, 097205 (2018).
[3] Y. Fan, et al., unpublished (2019).