Temperature dependence of interlayer coupling in δ MnGa/(Ga,As,Mn)/δ MnGa trilayers

We present the temperature dependence of the interlayer coupling, from 15 to 300 K, in ferromagnet/semiconductor/ferromagnet trilayers with the nominal structure of 10 nm δMn60Ga40/GaAs (n monolayers)/20 nm δMn54Ga46 [n=6–16 monolayers (ML) nominally] grown on (001) GaAs substrates by molecular-beam epitaxy. Since compositional analysis showed a strong diffusion of Mn into the GaAs spacer layer, we represent the trilayer structure as MnGa/(Ga,As,Mn)/MnGa. The magnetic-circular-dichroism loops showed antiferromagnetic coupling between both MnGa layers for the samples with a spacer layer from 6 to 14 ML GaAs nominally in the whole temperature range. The temperature coefficient of the coupling field was found to be positive for 6–8 ML spacers and negative for 10–14 ML spacers. We interpret these facts as the competition between two (or more) coupling mechanisms. For the sample with a 16 ML GaAs spacer layer, the interlayer coupling was antiferromagnetic below 200 K, but ferromagnetic above 200 K.