First-principles investigation of the assumptions underlying model-Hamiltonian approaches to ferromagnetism ofimpurities in III-V semiconductors
- 24 March 2004
- journal article
- research article
- Published by American Physical Society (APS) in Physical Review B
- Vol. 69 (11), 115211
- https://doi.org/10.1103/physrevb.69.115211
Abstract
We use first-principles calculations for transition-metal impurities V, Cr, Mn, Fe, Co, and Ni in GaAs, as well as Cr and Mn in GaN, GaP, and GaSb, to identify the basic features of the electronic structures of these systems. The microscopic details of the hole state such as the symmetry and the orbital character, as well as the nature of the coupling between the hole and the transition-metal impurity, are determined. This could help in the construction of model Hamiltonians to obtain a description of various properties beyond what current first-principles methods are capable of. We find that the introduction of a transition-metal impurity in III-V semiconductor introduces a pair of levels with symmetry—one localized primarily on the transition-metal atom, referred to as crystal-field resonance (CFR), and the other localized primarily on the neighboring anions, referred to as the dangling bond hybrid (DBH). In addition, a set of nonbonding states with e symmetry, localized on the transition-metal atom, are also introduced. Each of the levels is also spin split. Considering Mn in the host crystal series we find that while in GaN the hole resides in the level deep in the band gap, in GaAs and GaSb it resides in the level located just above the valence-band maximum. Thus, a DBH-CFR level anticrossing exists along this host-crystal series. A similar anticrossing occurs for a fixed host crystal (e.g., GaAs) and changing the impurity along the series: V in GaAs represents a DBH-below-CFR limit, whereas Mn corresponds to the DBH-above-CFR case. Consequently, the identity of the hole-carrying orbital changes. The symmetry vs and the character (DBH vs CFR), as well as the occupancy of the gap level, determine the magnetic ground state favored by the transition-metal impurity. LDA+U calculations are used to model the effect of pushing the occupied Mn states deeper into the valence band by varying U. We find that this makes the DBH state more hostlike, and at the same time diminishes ferromagnetism. While the spin-splitting of the host valence band in the presence of the impurity has been used to estimate the exchange coupling between the hole and the transition-metal impurity, we show how using this would result in a gross underestimation of the coupling.
Keywords
This publication has 62 references indexed in Scilit:
- Low-Dimensional SpinSystem at the Quantum Critical Limit:Physical Review Letters, 2003
- A Group-IV Ferromagnetic Semiconductor: Mn
x
Ge
1−
x
Science, 2002
- Theory of ferromagnetism in planar heterostructures of (Mn,III)-V semiconductorsPhysical Review B, 2001
- Room temperature ferromagnetic properties of (Ga, Mn)NApplied Physics Letters, 2001
- Magnetic properties of P-type GaMnP grown by molecular-beam epitaxyApplied Physics Letters, 2001
- Ferromagnetism in Magnetically Doped III-V SemiconductorsPhysical Review Letters, 2001
- Room-Temperature Ferromagnetism in Transparent Transition Metal-Doped Titanium DioxideScience, 2001
- Making Nonmagnetic Semiconductors FerromagneticScience, 1998
- New theoretical approach of transition-metal impurities in semiconductorsPhysical Review B, 1989
- Transition-metal impurities in III-V compoundsJournal of Physics C: Solid State Physics, 1985