Angle-Dependent Magnetoresistance Induced by Interface-Generated Spin Current in RuO_2/Permalloy Heterostructures

Altermagnets, a recently discovered class of magnetic materials exhibiting ferromagnetic-like
spin-split bands and antiferromagnetic-like compensated magnetic order, have attracted signifi-
cant interest for next-generation spintronic applications. Ruthenium dioxide (RuO2) has emerged
as a promising altermagnetic candidate due to its compensated antiparallel magnetic order and
strong spin-split electronic bands. However, recent experimental and theoretical reports also sug-
gest that RuO2 may be non-magnetic in its ground state, underscoring the need for deeper in-
vestigations into its magnetic character. Specifically, the (100)-oriented RuO2 films are expected
to generate spin currents with transverse spin polarization parallel to the N´eel vector. Here, we
investigate magnetotransport in epitaxial RuO2/Permalloy (Py) heterostructures to examine spin
Hall magnetoresistance and interfacial effects generated in such systems. Our measurements re-
veal a pronounced negative angular-dependent magnetoresistance for variation of magnetic field
direction perpendicular to the charge current direction. Detailed temperature-, magnetic field-,
and crystallographic orientation-dependent measurements indicate that interface-generated spin
current (IGSC) at the RuO2/Py interface predominantly governs the observed magnetoresistance.
In addition, the role of IGSC contribution to the observed magnetoresistance was demonstrated
through drift-diffusion calculations. This shows that strong interface effects dominate over possible
altermagnetic contributions from RuO2. Our results show that the role of interface-generated spin
currents is crucial and should not be overlooked in studies of altermagnetic systems. A critical
step in this direction is disentangling interfacial from altermagnetic contributions. The insight into
interfacial contributions from altermagnetic influences is essential for the advancement of RuO2-
based spintronic memory and sensing applications.