  Interfacial two-dimensional electron gas (2DEG) formed at the perovskite-type
oxide, such as SrTiO3, has attracted significant attention due to its
properties of ferromagnetism, superconductivity, and its potential application
in oxide-based low-power consumption electronics. Recent studies have
investigated spin-to-charge conversion at the STO interface with different
materials, which could affect the efficiency of this 2DEG interface. In this
report, we presented an Ar^+ ion milling method to create a 2DEG at STO
directly by inducing oxygen vacancies. To quantify the spin-to-charge
conversion of this interface, we measured the angular-dependent spin-torque
ferromagnetic resonance (ST-FMR) spectra, revealing an unconventional spin
polarization at the interface of Argon ion-milled STO and NiFe. Furthermore, a
micromagnetic simulation for angular-dependent spin-torque ferromagnetic
resonance (ST-FMR) has been performed, confirming the large unconventional spin
polarization at the interface.
