Physics – Condensed Matter – Materials Science
Scientific paper
2009-03-14
Phys. Rev. B 79, 235202 (2009)
Physics
Condensed Matter
Materials Science
13 pages, 13 figures. Submitted to PRB
Scientific paper
10.1103/PhysRevB.79.235202
The percentage of substitutional doping of magnetic atoms (Mn) in group-IV-based dilute magnetic semiconductors (DMS) can be increased by co-doping with another conventional electronic dopant (e-dopant) [Zhu et al., Phys. Rev. Lett. 100, 027205 (2008)]. Here, we report extensive theoretical investigations of the kinetic and thermodynamic characteristics of several co-doped systems including bulk Si and Ge as hosts and various group-III and group-V e-dopants. The main findings are as follows: The n-p pairing of n-type e-dopants with p-type substitutional Mn is energetically stable in bulk Ge and Si. Mn atoms move from interstitial sites to substitutional sites easier in the presence of a neighboring n-type e-dopant. Magnetic coupling between two Mn atoms in bulk Ge oscillates between positive (ferromagnetic) and negative (antiferromagnetic) values with increasing Mn-Mn distance, but in Mn/As co-doped Ge the coupling parameter remains positive at all distances beyond nearest-neighbors and this qualitative difference does not change with the doping level. For Mn doped Si, all coupling values except for the nearest neighbor one are positive and do not change much upon co-doping. We find an unconventional magnetic anisotropy in the co-doped system, that is, the dependence of magnetic coupling on the relative positions of the magnetic ions and their neighboring e-dopants. We employ Monte Carlo simulations to estimate the Curie temperature (Tc). We find that in Mn doped Ge no ferromagnetic order exists for Mn concentrations ranging from 3.13% to 6%. Instead, a spin-glass phase transition occurs at ~5K at 5% Mn doping. For Mn/As co-doped Ge, Tc increases nearly linearly with the Mn concentration and reaches 264K at 5% Mn doping.
Chen Hua
Kaxiras Efthimios
Zhang Zhenyu
Zhu Wenguang
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