Neutron-diffraction studies of zinc-blende MnTe epitaxial films and MnTe/ZnTe superlattices: The effect of strain and dilution on a strongly frustrated fcc antiferromagnet

Abstract

We report neutron-diffraction studies of antiferromagnetism in various forms of epitaxially grown zinc-blende (ZB) MnTe: in semibulk (\ensuremath{\sim}1 \ensuremath{\mu}m thick) single-crystal films of pure MnTe, in its magnetically diluted derivative ${\mathrm{Zn}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$Te with 0.695x1, and in strongly strained very thin (30--300 \AA{}) single-crystal MnTe layers in MnTe/ZnTe superlattices. ZB Mn chalcogenides are unique exmples of fcc Heisenberg antiferromagnets (AF) with dominant nearest-neighbor interactions. Such a lattice is one of the basic models of topologically frustrated spin systems. Only ZB MnS can be obtained through natural crystallization (and only in a fine powder form, which seriously limits the scope of possible studies on this system). The single-crystal forms of MnTe obtained using molecular-beam epitaxy have made it possible to study the influence of strain on a frustrated fcc antiferromagnet. We observe that such built-in strain strongly affects the domain structure as well as the phase-transition behavior. Furthermore, high-resolution x-ray diffraction reveals pronounced magnetostriction effects in the MnTe films. Both neutron as well as x-ray data indicate a rather unusual effect of a strong temperature shift in the relative populations of two inequivalent AF domain states, and a magnetostriction mechanism underlying this phenomenon is proposed. Finally, the data obtained on ${\mathrm{Zn}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$Te films complement the results of previous magnetic studies on bulk forms of this material with x\ensuremath{\le}0.68.