June 24, 2003
Applying the dynamical coherent potential approximation to a simple model, we have theoretically studied the behavior of the optical bandedge in diluted magnetic semiconductors (DMSs). For $A^{\rm II}_{1-x}$Mn$_{x}B^{\rm VI}$-type DMS, the present study reveals that the linear relationship between exchange-spitting $\mit\Delta E_{ex} $ and the averaged magnetization $|x < S_z >|$ widely holds for different values of $x$. The ratio, $\mit\Delta E_{ex}/x < S_z>$, however, depends not only the exchange strength but also the band offset. Furthermore, the present study reveals that in the low dilution of Ga$_{1-x}$Mn$_x$As the optical bandedge exists not at the bandedge of the impurity band but near the bottom of host band. The optical bandedge behaves as if the exchange interaction is ferromagnetic although the antiferromagnetic exchange interaction actually operates at Mn site. We conclude that the spin-dependent shift of the carrier states between the impurity band and host band accompanying with the change of magnetization causes the apparently ferromagnetic behavior of the optical bandedge which was reported in the magnetoreflection measurement of Ga$_{1-x}$Mn$_x$As.
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March 15, 2003
Applying the dynamical coherent potential approximation to a simple model, we have systematically studied the carrier states in $A_{1-x}$Mn$_xB$-type diluted magnetic semiconductors (DMS's). The model calculation was performed for three typical cases of DMS's: The cases with strong and moderate exchange interactions in the absence of nonmagnetic potentials, and the case with strong attractive nonmagnetic potentials in addition to moderate exchange interaction. When the exchan...
March 20, 2003
There are two competing views of itinerant ferromagnetism, the first viewing ferromagnetism as resulting from the indirect coupling between local moments via the itinerant carrier dynamics, the so-called RKKY mechanism, while in the alternative picture, ferromagnetism results from the spin polarization of itinerant carriers by the strong atomic Hund interaction - the so-called double exchange (DE) scenario. Which view describes the ferromagnetism in diluted magnetic semicondu...
January 30, 2012
The expected features of diluted magnetic semiconductors still remain in controversial issue, concerning whether or not s, p-d (f) exchange interactions indeed modify the host semiconductor band structure. To solve this doubt, a new scheme for measuring magneto-optical (MO) effect is developed, called magnetic photoresistance circular dichroism (PR-MCD), which detects the differential photoresistance of materials between two circularly polarized excitations. That allows us to...
January 20, 2016
We propose a method to realize diluted magnetic semiconductors (DMS) with p- and n-type carriers by choosing host semiconductors with a narrow band gap. By employing a combination of the density function theory and quantum Monte Carlo simulation, we demonstrate such semiconductors using Mn-doped BaZn2As2, which has a band gap of 0.2 eV. In addition, we found a new non-toxic DMS Mn-doped BaZn2Sb2, of which the Curie temperature Tc is predicted to be higher than that of Mn-dope...
August 9, 2002
A microscopic Hamiltonian for interacting manganese impurities in diluted magnetic semiconductors (DMS) is derived. It is shown that in p -type III-V DMS the indirect exchange between Mn impurities has similarities with the Zener mechanism in transition metal oxides. Here the mobile holes and localized states near the top of the valence band play the role of unoccupied oxygen orbitals which induce ferromagnetism. The Curie temperature estimated from the proposed kinematic exc...
November 14, 2005
The zinc-blende GaAs-based III-V diluted magnetic semiconductors (DMS)are studied in the coherent potential approximation(CPA). In this work, we use the exact Hilbert transformation of the face-centered cubic(fcc) density of states (DOS), which is different from the usual semi-circle density of states employed in our previous work. Our calculated relation of ground-state energy and impurity magnetization shows that ferromagnetism is always favorable at low temperatures. For v...
July 27, 2010
The magneto-optical properties of the ferromagnetic semiconductor Ga$_{1-x}$Mn$_{x}$As are studied within the dynamical mean-field approximation (DMFA). A material-specific multiband $sp^{3}$ tight-binding Hamiltonian is employed for the dispersion of the GaAs host. The calculated density of states shows an impurity band and a distorted valence band for large and moderate values of magnetic coupling, respectively. Upon using the more realistic band structure, the ferromagneti...
July 1, 2009
We employ Faraday and Kerr effect spectroscopy in the infrared range to investigate the electronic structure of Ga1-xMnxAs near the Fermi energy. The band structure of this archetypical dilute-moment ferromagnetic semiconductor has been a matter of controversy, fueled partly by previous measurements of the unpolarized infrared absorption and their phenomenological impurity-band interpretation. The infrared magneto-optical effects we study arise directly from the spin-splittin...
November 6, 2015
After more than a decade of intensive research in the field of diluted magnetic semiconductors (DMS), the nature and origin of ferromagnetism, especially in III-V compounds is still controversial. Many questions and open issues are under intensive debates. Why after so many years of investigations Mn doped GaAs remains the candidate with the highest Curie temperature among the broad family of III-V materials doped with transition metal (TM) impurities ? How can one understand...
December 9, 2010
For already a decade the field of diluted magnetic semiconductors (DMS) is one of the hottest. In spite of the great success of material specific Density Functional Theory (DFT) to provide accurately critical Curie temperatures ($T_{C}$) in various III-V based materials, the ultimate search for a unifying model/theory was still an open issue. Many crucial questions were still without answer, as for example: Why, after one decade, does GaMnAs still exhibit the highest $T_{C}$?...