Photoinduced spin angular momentum transfer into an antiferromagnetic insulator

Spin angular momentum transfer into an antiferromagnetic (AFM) insulator is observed in a single-crystalline Fe/CoO/MgO(001) heterostructure by time-resolved magneto-optical Kerr effect. The transfer process is mediated by the Heisenberg exchange coupling between Fe and CoO spins. Spin angular momentum transfer to ordered AFM spins is independent of the external magnetic field and enhances the spin precession damping in Fe, which remains nearly invariant with temperature.

Figure 1

(a) Schematic presentation of magnetization (M) precession in Fe/CoO heterostructure with the magnetic field $H$ applied along the Fe [110]. (b) TRMOKE data at 78 K measured with a magnetic field of $H$ = 600 Oe. The solid line is a fit by the damped sine function, and the inset shows the Fourier power spectrum. (c) Longitudinal hysteresis loops for magnetic field along uniaxial easy axis [100] and hard axis [010] at 82 K and 330 K. (d) Temperature dependence of coercivity ($H_c$) and exchange biasing field ($H_e$) obtained from easy axis loops. All data are measured from Fe film grown on 2.5-nm-thick CoO (001) layer.

Figure 2

Magnetic field $H$ dependence of (a)–(c) effective Gilbert damping α obtained from Eq. (1) and (d)–(f) precession frequency $f$ with $H$ applied along Fe[110] at 78 K, 240 K, and 300 K, respectively. The curves in (d)–(f) are fits of Eq. (2). The damping and frequency data obtained by TRMOKE from Fe film grown on 2.5-nm-thick CoO (001) layer and Fe/MgO are presented by ■ and ▼, respectively.

Figure 3

Temperature $T$ dependence of (a) effective Gilbert damping α and UMA field $2K_u/M_s$ and (b) precession frequency of Fe film grown on 2.5-nm-thick CoO (001) layer. ▲ and ♦ present the damping data in (a) and frequency data in (b), measured using $H$ = 1920 Oe and 500 Oe applied along Fe[110], respectively. o represents the UMA field. The dashed line indicates the Néel temperature $T_{\mathrm{N}}$. The solid line is the calculated α using Eq. (4) with η = 1.

Figure 4

(a) Precession frequency and damping in Fe films grown on 1-nm- and 4-nm-thick CoO layer at 78 K and 300 K. (b) Schematic channel of spin angular momentum transfer from FM to AFM spins and to lattice. The exchange coupling between FM and AFM spins and the spin-orbital coupling between AFM spins and lattice are represented by springs.

Figure 5

Simulation of dephasing-induced damping as a function of (a) field and (b) temperature below $T_{\mathrm{N}}$.