Variations of long- and short-range-order structural and magnetic properties of thermally annealed Mn/GaAs digital alloys

The crystal structure and local environment surrounding Mn atoms in Mn/GaAs digital layers thermally annealed at different temperatures have been investigated using x-ray diffraction and extended x-ray absorption fine structure methods. As the annealing temperature is increased, a satellite peak near the GaAs (004) diffraction line systematically shifts towards higher angles, indicating an apparent decrease of lattice parameters in the Mn/GaAs layers. When the annealing temperature is increased to 550 °C the satellite peak position moves dramatically from below to above the GaAs (004) peak, accompanied by a corresponding increase of Mn–As bond length from 2.48 to 2.56 Å, suggesting that the local structure around Mn changes from Ga substitution in GaAs to that of MnAs-like phase. Variations of the long- and short-range-order structures are believed to be related to the observed changes of magnetic properties including the disappearance of ferromagnetism in the sample annealed at 550 °C.