Biquadratic magnetic coupling effect in CoPt/Cr/Fe₉₀Co₁₀ orthogonal structures

In this work, we present the biquadratic field H _bq contribution to increase a frequency of spin-torque oscillation (STO) in an orthogonal magnetization structure in simulation, and realize such an orthogonal structure by preparing Co/Pt lamination as the bottom perpendicular magnetic anisotropy layer, Cr or Cu as the spacer, and experimentally realize Fe₉₀Co₁₀ as the top free layer. Our observations of the Cr-spacer sample reveal a notable challenge in achieving magnetic saturation, underscoring the role of H _bq in suppressing magnetization reversal and its potential to broaden the STO current range and increase the STO frequency. This leads to the manifestation of spin-transfer-torque oscillations in an orthogonal structure, bolstered by robust biquadratic magnetic coupling, thus attaining high and stable STOs in the simulations.