Switching Time of Spin-Torque-Driven Magnetization in Biaxial Ferromagnets

We analytically model the magnetization switching time of a biaxial ferromagnet driven by an antidampinglike spin torque. The macrospin magnetization dynamics is mapped to an energy-flow equation, wherein a rational-function approximation for the elliptic integrals for moderate spin current and small damping results in a closed-form expression for the switching time. The randomness in the initial angle of magnetization gives the distribution function of the switching time. The analytical model conforms to results obtained from Monte Carlo simulation for a broad range of material parameters. Our results can improve the design and benchmarking of in-plane spin-torque magnetic memory by obviating the need for expensive numerical computation.