Temperature dependence of interlayer coupling in delta MnGa/(Ga,As,Mn)/delta 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 delta Mn60Ga40/GaAs (n monolayers)/20 nn delta Mn54Ga46 [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. (C) 1997 American Institute of Physics.