Critical current density of a spin-torque oscillator with an in-plane magnetized free layer and an out-of-plane magnetized polarizer

Spin-torque induced magnetization dynamics in a spin-torque oscillator with an in-plane (IP) magnetized free layer and an out-of-plane (OP) magnetized polarizer under IP shape-anisotropy field ($H_{\mathrm{k}}$) and applied IP magnetic field ($H_{\mathrm{a}}$) was theoretically studied based on the macrospin model. The rigorous analytical expression of the critical current density ($J_{\mathrm{c}1}$) for the OP precession was obtained. The obtained expression successfully reproduces the experimentally obtained $H_{\mathrm{a}}$-dependence of $J_{\mathrm{c}1}$ reported in [D. Houssameddine $et$ $al$., Nat. Mater. 6, 447 (2007)].