Strong Interfacial Exchange Field in a Heavy Metal/Ferromagnetic Insulator System Determined by Spin Hall Magnetoresistance

Spin-dependent transport at heavy metal/magnetic insulator interfaces is at the origin of many phenomena at the forefront of spintronics research. A proper quantification of the different interfacial spin conductances is crucial for many applications. Here, we report the first measurement of the spin Hall magnetoresistance (SMR) of Pt on a purely ferromagnetic insulator (EuS). We perform SMR measurements in a wide range of temperatures and fit the results by using a microscopic model. From this fitting procedure, we obtain the temperature dependence of the spin conductances (G s, G r, and G i), disentangling the contribution of field-like torque (G i), damping-like torque (G r), and spin-flip scattering (G s). An interfacial exchange field of the order of 1 meV acting upon the conduction electrons of Pt can be estimated from G i, which is at least three times larger than G r below the Curie temperature. Our work provides an easy method to quantify this interfacial spin-splitting field, which plays a key role in emerging fields such as superconducting spintronics and caloritronics as well as topological quantum computation.