Carrier-Mediated Antiferromagnetic Interlayer Exchange Coupling in Diluted Magnetic Semiconductor Multilayers ${\mathrm{Ga}}_{1-x}{\mathrm{Mn}}_x\mathrm{As}/\mathrm{GaAs}\mathrm{\text{:}}\mathrm{Be}$

We report the antiferromagnetic (AFM) interlayer exchange coupling between ${\mathrm{Ga}}_{0.97}{\mathrm{Mn}}_{0.03}\mathrm{As}$ ferromagnetic semiconductor layers separated by Be-doped GaAs spacers. Polarized neutron reflectivity reveals a characteristic splitting at the wave vector corresponding to twice the multilayer period, indicating that the coupling between the ferromagnetic layers is AFM. When the applied field is increased to above the saturation field, this AFM coupling is suppressed. This behavior is not observed when the spacers are undoped, suggesting that the observed AFM coupling is mediated by doped charge carriers.

Figure 1

Temperature dependence of magnetization of ${\mathrm{Ga}}_{0.97}{\mathrm{Mn}}_{0.03}\mathrm{As}/\mathrm{GaAs}$ (a) and ${\mathrm{Ga}}_{0.97}{\mathrm{Mn}}_{0.03}\mathrm{As}/\mathrm{GaAs}\mathrm{\text{:}}\mathrm{Be}$ (b) multilayers. The data were collected while cooling, with the magnetic field applied along the [100] direction.

Figure 2

(a) Unpolarized and polarized neutron reflectivities of the Be-doped and the undoped multilayers with the field applied along the [110] direction. The curves are shifted vertically for clarity. The solid lines are fits to the data using the models described in the text. The AFM and the FM splittings of the Be-doped sample are emphasized by $R\times Q^4$ curves in (b) and (c), respectively.

Figure 3

The AFM (a) and the FM (b) splittings in the NSF reflection intensities of the Be-doped sample measured at 7 K. The data were collected sequentially in the order from top to bottom, and corresponding applied fields are shown in the middle. The lines through the data are guides for the eye. The illustrations in the middle column schematically show the spin orientations in the multilayer at corresponding fields.

Figure 4

The AFM (a) and the FM (b) splittings in the NSF reflection intensities of the Be-doped sample measured at 30 K.