Relaxation Times for Magnetization Reversal in a High Coercivity Magnetic Thin Film

We used a magneto-optical Kerr effect microscope to measure 180° magnetization reversal in a high coercivity ${\mathrm{CoCr}}_{10}{\mathrm{Ta}}_4$ thin film subjected to nanosecond field pulses. Exponential magnetization decay occurs for pulse duration $t_p<10\mathrm{ns}$ followed by logarithmic decay for $t_p>10\mathrm{ns}$, indicating a crossover from nonequilibrium magnetization relaxation at short $t_p$ to metastable equilibrium and thermal relaxation for longer $t_p$. We conclude that the nonequilibrium magnetization relaxation time $\left({\tau }_n\right)$ and that the average relaxation time of microscopic thermal fluctuations $\left({\tau }_0\right)$ is ${\tau }_n={\tau }_0\approx 5\mathrm{ns}$.