Charge Transport in the Impurity Band of Dilute Magnetic Semiconductors: Experiment and Theory
Final Report Abstract
The main results of this project are: 1) Discovery of a novel mechanism of the positive magnetoresistance in dilute magnetic semiconductors in the hopping charge transport regime proven for dilute magnetic semiconductors at impurity concentrations below the metal-insulator transition. 2) Theoretical description of this mechanism based on scaling arguments. The essence of the novel mechanism can be formulated as follows. Due to s-d exchange interactions between the spins of electrons localized on donors (e.g. Cl atoms in Zn1-x MnxSe:Cl) and the magnetic moments of magnetic ions (e.g. Mn atoms in Zn1-x MnxSe:Cl) the energies of electrons on donors depend on the alignment of the magnetic moments of magnetic ions in the external magnetic field. Due to a random distribution of magnetic atoms surrounding donors, the exchange interaction leads to a broadening of the donor energy distribution when the Mn spins are aligned by magnetic field. The broader the energy distribution of donors is, the larger the resistivity of the material is. Herewith the exchange interaction between electrons localized on donors with randomly distributed magnetic atoms leads to a positive magnetoresistance. Theoretical description of the effect has been formulated using the scaling consideration based on the remarkable feature of the microscopic transition rates for charge carriers in the hopping transport regime. When all energies, temperature and electric field are scaled by some factor, the hopping rates and concomitantly the current density remain unchanged. This feature of the microscopic transition rates enables one to provide an elegant and transparent description of the novel effect of the positive magnetoresistance. The results have been verified by straightforward computer simulations.
Publications
- Scaling approach to hopping magnetoresistivity in dilute magnetic semiconductors. Physical Review B, Vol. 88. 2013, Issue 11, 115210.
A. V. Nenashev, F. Jansson, M. Wiemer, S. Petznick, P. J. Klar, M. Hetterich, A. V. Dvurechenskii, F. Gebhard, S. D. Baranovskii
(See online at https://doi.org/10.1103/PhysRevB.88.115210) - Large positive magnetoresistance effects in the dilute magnetic semiconductor (Zn,Mn)Se in the regime of electron hopping. Journal of Applied Physics, Vol. 116.2016, Issue 8, 083710.
F. Jansson, M. Wiemer, A. V. Nenashev, S. Petznick, P.J. Klar, M. Hetterich, F. Gebhard, S. D. Baranovskii
(See online at https://doi.org/10.1063/1.4894236) - Scaling description of positive magnetoresistivity in doped dilute magnetic semiconductors. Journal of Magnetism and Magnetic Materials, Vol. 383. 2015, pp. 44–49.
A. V. Nenashev, F. Jansson, S. Petznick, M. Wiemer, P.J. Klar, A. V. Dvurechenskii, F. Gebhard, S. D. Baranovskii
(See online at https://doi.org/10.1016/j.jmmm.2014.11.069)
