Scaling approach to hopping magnetoresistivity in dilute magnetic semiconductors

Abstract

We suggest a mechanism causing large positive magnetoresistance (MR) in dilute magnetic semiconductors when hopping via nonmagnetic donor impurities dominates the conductivity. The effect is due to the increase in the characteristic width σ of the donor energy distribution with increasing magnetic field B, caused by exchange interactions between magnetic Mn atoms and the electrons localized on nonmagnetic Cl donor impurities. Using general scaling arguments based solely on the dependencies of hopping rates on temperature and on the energies of hopping sites we show that this mechanism accounts quantitatively for our experimental data on MR in n-type Zn 1−x Mn x Se:Cl. We suggest a method for extracting the dependence of σ on magnetic field from the MR data. The mechanism explains the experimentally observed universal dependence of the MR effect on the ratio B/T at different temperatures T under the premise that transport is due to the nearest-neighbor or Mott hopping mechanism.

Large positive magnetoresistance effects in the dilute magnetic semiconductor (Zn,Mn)Se in the regime of electron hopping

“…2(c) illustrates that the magnetoresistance in ZnSe without Mn (sample (b)) is very different from that of the DMS samples, which evidences that the positive magnetoresistance considered in the current report is due to the presence of Mn, as suggested in Ref. 16. Moreover, in the range of Mn concentrations x studied, the positive magnetoresistance effects increase with increasing x for comparable donor concentrations.…”

“…3. As the hopping transport mobility depends exponentially on the width of the distribution of the donor site energies, 16,24 this explains qualitatively the dependence of the empirical fitting function Eq. (5) on magnetization M.…”

“…Mostly, the effect of Mn atoms was considered only by a mean-field approach, yielding a constant Mn concentration throughout the whole system. [13][14][15] In a previous study, 16 where a scaling theory for the resistivity of DMS was developed, we showed that magnetoresistance measurements in Zn 1Àx Mn x Se may be explained by magnetic-field induced broadening of the donor energy distribution (DOS), and that this broadening may be ascribed to the s-d exchange interaction between the donor electron spins and randomly distributed Mn 2þ spins, which tend to align with rising magnetic field. The scaling approach, however, takes into account only the width of the DOS and, hence, does not address the problem to which extent the shape of the energy distribution corresponding to the s-d exchange interaction affects the magnetoresistance curves.…”

Electron spin flip Raman spectroscopy of the diluted magnetic semiconductor Zn1‐xMnxSe below the metal‐insulator transition

“…It should be mentioned that the complementary part of the resonance profile, which originates from free-exciton intermediate These spectroscopy results agree very well with those of the magneto-transport experiments, which show a positive magneto-resistance up to 200% [7], which implies that the electron hopping processes are progressively hindered by the broadening of the level distribution. This broadening is explained quantitatively by a modelling of the Bdependent characteristic width σ of the donor energy distribution, using for the magneto-resistance general scaling arguments based solely on the dependence of hopping rates on temperature and on the energies of hopping sites [6].…”

“…a giant Faraday rotation, giant Zeeman splitting, and a very pronounced magnetoresistance [5]. The latter aspect is especially relevant in the doping range slightly below the Mott density, where transport is dominated by hopping processes in the impurity band [6,7].…”