Long-range antiferromagnetic couplings in [ZnTe|MnTe] superlattices

Magnetic semiconductor superlattices consisting of x monolayers of ZnTe alternated with y monolayers of MnTe [(ZnTe)x|(MnTe)y] have been grown in the zinc-blende structure by molecular beam epitaxy. For relative thin ZnTe nonmagnetic interlayers (3⩽x⩽6), neutron diffraction data show long range order within the MnTe layers and also an interlayer magnetic coupling across the semiconducting ZnTe interlayer extending over multiple bilayers. For the x=5, y=10; and x=4, 5, y=20 superlattices at low temperature (10 K), the spins in adjacent MnTe layers couple in an inphase antiferromagnetic structure with identical spin orientations in all MnTe layers. As the temperature is raised, this ordering slowly transforms into an antiphase coupling in which alternate MnTe layers have spin directions reversed. For increasing ZnTe layer thickness, a systematic reduction in the magnetic correlation range is observed, with the correlation range reducing to approximately one MnTe layer for x=6 and 7.