Anisotropic superexchange and spin-resonance linewidth in diluted magnetic semiconductors

Abstract

The Dzyaloshinski-Moriya (DM) anisotropic superexchange constant and the resulting electronparamagnetic-resonance (EPR) linewidth in Mn-based II-VI-compound diluted magnetic semiconductors {DMS) such as Cd 1 Mn Te are calculated quantitatively.An Anderson Hamiltonian, developed in a previous study of isotropic superexchange, describing correlated Mn 3d states hybridized with semiconducting sand p-derived levels, is generalized to include the anion spin-orbit coupling responsible for anisotropic superexchange. DM exchange is shown to be the dominant anisotropic interaction, with magnitude -Sgo of isotropic superexchange. The EPR line shape is calculated with use of a moment expansion of the magnetic response function to first order in inverse temperature together with a maximum-entropy ansatz. The calculated infinite-temperature linewidths are in good agreement with extrapolated experimental values. A novel fit of the theoretical temperature dependence to existing experimental linewidth data provides the first empirical value for the anisotropic exchange constant, in excellent agreement with the theoretical value. Calculated chemical trends for the exchange constants yield the experimentally expected linewidth trends.

Diluted Magnetic Semiconductors in High Magnetic Fields

“…The same analysis also gave an estimate for the DM constant D1 . All these results (magnitude and sign of ΔJ1, and value of D1) agree with theory [8,18].…”

“…Among the other interactions between the magnetic ions the most important is the Dzyaloshinski-Moriya (DM) interaction, of the form The largest Dij is expected to be D1. Its magnitude for Mn-based DMS was calculated by Larson and Ehrenreich [8]. They found that it increases with the atomic number of the anion.…”

Superexchange in AIIBVIDiluted Magnetic Semiconductors with Mn, Fe and Co Ions

“…The former repreSent the contribution from all singly occupied ionic orbitals, whereas the latter the contribution from the doubly occupied eg orbitals. After putting S = 5/2 and noting that in Mn 2 + ions all 5d-orbitals are singly occupied, one gets from (3) the results compatible with those of Larson and Ehrenreich [6].…”

“…Using a perturbative k-space approach Larson et al [5] have shown that the superexchange, reSulting from sp-d hybridization, is by far the dominant spin-spin interaction mechanism in AIIBVI DMS. In papers [5] and [6] the authors, considering the case of the S-like Mn2 ± magnetic ion, have used the simplest Anderson model to approximate the ionic energy spectrum. Furthermore, in the calculations of isotropic exchange [5] the ionic orbital dependence of the hybridization Hamiltonian was neglected.…”

“…[1]). The indirect exchange [2][3][4], aS well as the superexchange [5,6] were invoked to account for the observed isotropic (Heisenberg) and anisotropic (Dzyaloshinski-Moriya) exchange . constants.…”