Hyperfine fields in an Ag/Fe multilayer film investigated with ${}^8\text{L}\text{i}$ $\beta$-detected NMR

Low-energy $\beta$-detected nuclear magnetic resonance was used to investigate the spatial dependence of the hyperfine magnetic fields induced by Fe in the nonmagnetic Ag of an Au(40 Å)/Ag(200 Å)/Fe(140 Å) (001) magnetic multilayer grown on GaAs. The resonance line shape in the Ag layer shows dramatic broadening compared to that of intrinsic Ag. This broadening is attributed to large magnetic fields induced in this layer by the magnetic Fe layer. We find that the induced hyperfine field in the Ag follows a power law decay away from the Ag/Fe interface with power $-1.93\left(8\right)$, and a field extrapolated to 0.23(5) T at the interface.

Figure 1

(Color online) $\beta \text{-NMR}$ spectra measured in the MML sample at room temperature and a field of 4.5 T at implantation energy (a) 30.5, (b) 4, and (c) 3.5 keV. The solid red lines are best fits to the calculated line shapes (see text). The dotted and dashed lines represent the contributions from ${}^8\text{L}\text{i}$ in Ag and Au, respectively.

Figure 2

(Color online) Percentage of ${}^8\text{L}\text{i}$ stopping in each layer of the MML sample as a function of implantation energy, calculated using TRIM.SP Monte Carlo simulation.

Figure 3

(Color online) ${}^8\text{L}\text{i}$ stopping profile in the MML sample generated using TRIM.SP Monte Carlo simulations for implantation energies of 3.5, 4.0, and 30.5 keV. At lower energies ${}^8\text{L}\text{i}$ stops predominantly in the Ag layer, while at the full energy nearly all ${}^8\text{L}\text{i}$ stops in the GaAs substrate.

Figure 4

Simulated line shape, in an applied field $B_{\text{ext}}$, generated for induced hyperfine fields that follows (a) an oscillating distribution described by Eq. (1) and (b) a uniform distribution within the envelope described by Eq. (2). Both line shapes were calculated using $\lambda =11.7\text{Å}$, $\alpha =-1.9$, $B_0=0.23\text{T}$, and $B_{\text{ext}}=4.5\text{T}$.