Effective exchange fields in spin-torque resonance of magnetic insulators

• We model spin-torque FMR spectra of magnetic insulators.
• The imaginary part of the spin mixing conductance may be anisotropic.
• The phase shift between ac current and Oersted field should be studied.

We report additional results on the spin-torque ferromagnetic resonance (ST-FMR) of a bilayer system made from a magnetic insulator such as Y3Fe5O12Y3Fe5O12 (YIG) and a heavy normal metal such as Pt in terms of the interface spin-mixing conductance and including spin pumping. We analyze experimental ST-FMR spectra for out-of-plane and in-plane magnetization configurations in terms of an anisotropic imaginary part Gi of the mixing conductance (or interface effective field). The estimated ratio between imaginary and real parts Gi/Gr≲0.3Gi/Gr≲0.3 is sensitive to an (unknown) phase shift between microwave current bias and associated Oersted field.