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Magnetic Semiconductors (magnetic + semiconductor)

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Physics and Astronomy	100%

Selected Abstracts

Magnetic semiconductors in ternary Cd,Mn,Te compounds

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 5 2008
Yong Liu
Abstract Since Mn-doped CdTe in zincblende structure has been fabricated for Mn concentrations from 0 to 0.5, we use a first-principles full-potential method to study CdTe-based ternary Cd,Mn,Te compounds for possible magnetic semiconductors. The compounds are constructed by substituting Mn for some Cd atoms in zincblende CdTe. We optimize fully their geometric structures and internal atomic positions, and then study their electronic and magnetic properties. We find that the stable CdMnTe2 and Cd3MnTe4 are antiferromagnetic semiconductors with space groups 160 and 111, and the stable Cd7MnTe8 is a layered ferromagnetic semiconductor with space group 115. Their real lattice constants are a little smaller than CdTe's and an Mn atom contributes 5 Bohr magnetons to their total magnetic moments. The antiferromagnetism for the CdMnTe2 is attributed to the Te-based superexchange of Mn spins. For the other two, the MnMn spin interactions are dependent on the MnMn distance and the environment. The antiferromagnetism for the Cd3MnTe4 and the layered ferromagnetism for the Cd7MnTe8 can be attributed to two weaker indirect exchange interactions based on both Cd and Te. The Kohn,Sham gaps of the three magnetic semiconductors are 0.52 eV, 0.80 eV, and 1.23 eV, respectively. The real semiconductor gaps may be larger than 1 eV considering the fact that the Kohn,Sham gap of CdTe is 0.55 eV but the experimental semiconductor gap is 1.56 eV at 300 K. These magnetic semiconductors, compatible with semiconductors such as CdTe, could be useful in spintronics applications. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Light scattering study on hybrid structures of Zn1,x,yCdxMnySe quantum wells with ferromagnetic Co wires

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2004
M. Sakuma
Abstract Sub-micron scale hybrid structures of Zn1,x,yCdxMnySe diluted magnetic semiconductor (DMS) quantum wells (QWs) with ferromagnetic Co wires have been fabricated for the purpose of applying local magnetic fields to the DMS-QW. The wire of DMS-QW with the width down to 100 nm was sandwiched between the Co wires. The magneto-optical properties are studied by spin-flip light scattering of paramagnetic Mn-ions in the DMS. The application of uniform magnetic fields higher than 0.25 T has been attained from the Co wires to the DMS-QWs. In addition, the field application from the Co to the DMS-QWs is switched on by weak magnetic fields of 0.03 T due to the magnetic shape anisotropy of the Co wires, which can realize the switching behavior of the spin alignment of Mn-ions in the DMS-QW. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Influence of the Mn compositional distribution on the magnetic order in diluted GaMnN layers

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008
D. Mai
Abstract GaMnN is a prototypical GaN-based dilute magnetic semiconductor (DMS) and its potential as a room temperature ferromagnetic material is still a controversial question to be answered. Diluted GaMnN layers with Mn concentrations up to several percent have been grown by plasma-assisted MBE on MOVPE-GaN templates either on p-Si(111) or on Al2O3(0001) substrates. None of the samples reported here shows second phase precipitates in XRD or in the TEM analysis. However different composition distributions have been evidenced by EDX during the scanning TEM analysis. GaMnN grown at a substrate temperature of TS = 650 °C exhibits extended structural defects and strong compositional inhomogeneity. This could be indicative of decomposition due to local strain. Samples grown at TS = 775 °C with a Mn concentration of about 3% show a homogeneous Mn distribution in the layer. The magnetic properties are found to vary from spin glass to ferromagnetic behaviour at room temperature among different samples. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Ternary magnetic semiconductors: recent developments in physics and technology

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2009
V. Tsurkan
Abstract Recent results in physics and technology of ternary magnetic oxide and chalcogenide spinels AB2X4 (A = Fe, Mn, Co, Cd, Zn, Hg; B = Cr, Co, Sc, Al; X = O, S, Se) are reviewed. Using magnetic susceptibility, specific heat, thermal expansion, electron-spin resonance, neutron diffraction, broad-band dielectric spectroscopy, and infrared optical spectroscopy, the spin, charge, orbital, and lattice correlations in these compounds were investigated. The novel magnetic ground states, e.g., spin liquid, spin,orbital liquid, and orbital glass, and in triguing effects, like colossal magnetocapacitive coupling, negative thermal expansion, and spin-driven Jahn,Teller structural transformations were revealed. In considering the origin of these phenomena, the concept of geometrical and bond frustration is explored. It relates the interplay of charge, spin, and orbital degrees of freedom with the inherent topological frustration and competing exchange interactions between the magnetic ions. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Magneto-optical spectroscopy of spin injection and spin relaxation in ZnMnSe/ZnCdSe and GaMnN/InGaN spin light-emitting structures

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2007
I. A. Buyanova
Abstract In this paper we review our recent results from in-depth investigations of physical mechanisms which govern efficiency of several processes important for future spintronic devises, such as spin alignment within diluted magnetic semiconductors (DMS), spin injection from DMS to non-magnetic spin detectors (SDs) and also spin depolarization within SD. Spin-injection structures based on II,VIs (e.g. ZnMnSe/Zn(Cd)Se) and III,Vs (e.g. GaMnN/Ga(In)N) were studied as model cases. Exciton spin relaxation within ZnMnSe DMS, important for spin alignment, was found to critically depend on Zeeman splitting of the exciton states and is largely facilitated by involvement of longitudinal optical (LO) phonons. Optical spin injection in ZnMnSe/Zn(Cd)Se was shown to be governed by (i) commonly believed tunneling of individual carriers or excitons and (ii) energy transfer via localized excitons and spatially separated localized electron,hole pairs (LEHP) located within DMS. Unexpectedly, the latter mechanism is in fact found to dominate spin injections. We shall also show that spin depolarization in the studied structures is essentially determined by ef- ficient spin relaxation within non-magnetic spin detectors, which is an important factor limiting efficiency of spin detection. Detailed physical mechanisms leading to efficient spin depolarization will be discussed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Ferromagnetism in epitaxial Zn0.95Co0.05O films grown on ZnO and Al2O3

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 14 2006
K. Nielsen
Abstract In this article, the possible mechanisms resulting in strong ferromagnetic coupling in transition metal(TM)-doped ZnO and other diluted magnetic semiconductors (DMS) are reviewed and the prerequisites for the observation of room temperature ferromagnetism in TM-doped ZnO are defined. In order to study the ferromagnetic behavior we have grown epitaxial Zn0.95Co0.05O films simultaneously on (0001) ZnO and Al2O3 substrates by laser molecular beam epitaxy at different deposition temperatures. A systematic study of the structural and magnetic properties has been performed to reveal their interdependence. Room temperature ferromagnetism has been found in Zn0.95Co0.05O films grown on ZnO, whereas for films deposited on sapphire only weak ferromagnetic signals have been detected which could not unambiguously be separated from those of the substrate. The different behavior is explained by different structural properties and defect densities in both films. Our experimental findings are in good agreement with a spin split impurity band model, where strong ferromagnetic exchange in ZnO:Co2+ is obtained by a strong hybridization between the magnetic Co2+ ion states and the donor states due to a large density of native defects. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Magnetoresistivity model and ionization-energy approximation for ferromagnets

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 5 2009
Andrew Das Arulsamy
Abstract The evolution of resistivity versus temperature (, (T)) curve for different doping elements, and in the presence of various defects and clustering are explained for both diluted magnetic semiconductors (DMS) and manganites. Here, we provide unambiguous evidence that the concept of ionization energy (EI) which is explicitly associated with the atomic energy levels, can be related quantitatively to transport measurements. The proposed ionization energy model is used to understand how the valence states of ions affect the evolution of , (T) curves for different doping elements. We also explain how the , (T) curves evolve in the presence of, and in the absence of defects and clustering. The model also complements the results obtained from first-principles calculations. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Magnetic semiconductors in ternary Cd,Mn,Te compounds

Effects of dilution and disorder on magnetism in diluted spin systems

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2007
Guixin Tang
Abstract The influence of configurational disorder on the magnetic properties of diluted Heisenberg spin systems is studied with regard to the ferromagnetic stability of diluted magnetic semiconductors. The equation of motion of the magnon Green's function is decoupled by Tyablikov approximation. With supercell approach, the concentrations of magnetic ions are determined by the size of the supercell in which there is only one magnetic ion per supercell in our method. In order to distinguish the influence of dilution and disorder, there are two kinds of supercells being used: the diluted and ordered case and the diluted and disordered case. The configurational averaging of magnon Green function due to disorder is treated in the augmented space formalism. The random exchange integrals between two supercells are treated as a matrix. The obtained magnon spectral densities are used to calculate the temperature dependence of magnetization and Curie temperature. The results are shown as following: (i) dilution leads to increasing the averaged distance of two magnetic ions, further decreases the effective exchange integrals and is main reason to reduce Curie temperature; (ii) spatial position disorder of magnetic ions results in the dispersions of the exchange integrals between two supercells and slightly changes ferromagnetic transition temperature; (iii) the exponential damping of distance dependence obviously reduces Curie temperature and should be set carefully in any phenomenological model. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Nitrides as spintronic materials

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003
Tomasz Dietl
The Guest Editors of the Proceedings of the 5th International Conference on Nitride Semiconductors (ICNS-5), Hiroshi Amano and Takashi Udagawa, have nominated the invited presentation by Tomasz Dietl [1] as Editor's Choice of the present issue of physica status solidi (b). This paper is a progress report on spintronics-related issues in Mn-based III-nitrides as potential diluted magnetic semiconductors. The cover picture shows the computed values of the Curie temperature for various p-type III,V compounds containing 5% of Mn in the S = 5/2 high spin state and 3.5 × 1020 holes per cm3, predicting that TC should exceed room temperature in the Mn-based nitrides. Thomas Dietl is head of the Low-Temperature Physics Group and professor at the Institute of Physics of the Polish Academy of Sciences. He is one of the most experienced researchers in the area of ferromagnetic semiconductors, spin-related phenomena and other current topics of semiconductor physics with many publications and invited talks at conferences and seminars world-wide. The full Proceedings of the 5th International Conference on Nitride Semiconductors (ICNS-5) are published in physica status solidi (c) , conferences and critical reviews, Vol. 0, No. 7 (November 2003) (ISBN 3-527-40489-9). Conference papers can also be found in phys. stat. sol. (a) 200, No. 1 (2003). [source]

Ab initio theory of exchange interactions in itinerant magnets

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003
I. Turek
Abstract The paper reviews an ab initio two-step procedure to determine thermodynamic properties of itinerant magnets. In the first step, the selfconsistent electronic structure of a system is calculated using the tight-binding linear muffin-tin orbital method combined with Green function techniques. In the second step, the parameters of the effective classical Heisenberg Hamiltonian are determined using the magnetic force theorem and they are employed in subsequent evaluation of magnon spectra, the spin-wave stiffness constants and the Curie/Néel temperatures. Applicability of the developed scheme is illustrated by investigations of selected properties of 3d metals Fe, Co, and Ni, diluted magnetic semiconductors (Ga,Mn)As, and 4f metals Gd and Eu. [source]

Influence of non-random incorporation of Mn ions on the magnetotransport properties of Ga1,xMnxAs alloys

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2008
C. Michel
Abstract We study theoretically the influence of a spatially nonrandom incorporation of Mn ions on the magnetotransport in paramagnetic Ga1,xMnxAs alloys. Such a nonrandomness may be introduced during post-growth annealing treatment. We use a resistor-network model for describing the electrical transport of this disordered semiconductor system as a function of temperature and external magnetic field. The model is founded on classical semiconductor band-transport and neglects many-body interactions. The peculiarities of paramagnetic dilute magnetic semiconductors, in particular, the magnetic-field induced changes of the density of states, the broad acceptor-energy distribution, and the interplay of magnetic field independent disorder (due to the alloying of GaAs with Mn) and magnetic field dependent disorder (due to the the Giant Zeeman splitting) are accounted for in a mean-field fashion. We have previously shown that this empirical transport model based on reasonable assumptions and realistic material parameters yields a satisfactory quantitative description of the experimentally obtained temperature and magnetic-field dependence of the resistivity of Ga0.98Mn0.02As samples annealed at different temperatures. For Ga1,xMnxAs alloys annealed at temperatures above 500 °C where structural changes lead to the formation of MnAs clusters, the transport is dominated by the paramagnetic GaAs:Mn host matrix as the cluster density is below the percolation threshold. We will show that in this situation the transport results can only be explained accounting for a nonrandom Mn distribution. Thus the analysis shown here provides further understanding of the annealing-induced changes of the transport properties in dilute magnetic III-Mn-V semiconductors. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Local environment effects on exchange interactions in dilute magnetic semiconductors

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2006
K. Sato
Abstract We calculate effective exchange interactions in dilute magnetic semiconductors by taking local environment effects into account. The effects of local impurity configurations are considered by embedding a large cluster into the effective medium calculated by the Korringa-Kohn-Rostoker coherent potential approximation (KKR-CPA) method. Calculated exchange interactions by our cluster embedding method differ from those calculated by the Liechtenstein's method, because in our method the multiple scattering effect between site i and j is fully included. It is also found that the calculated exchange interactions strongly depend on the position of the impurities in the cluster other than site i and j. The average of the configuration dependent interactions approximately converge to the two impurity embedding results. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Effect of hydrostatic pressure on the transport properties in magnetic semiconductors

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2004
M. Csontos
Abstract The effect of pressure on the ferromagnetic phase transition has been studied in manganese doped III-V semiconductors by electrical conductance and Hall measurements. We found that the application of hydrostatic pressure shifts the transition temperature upwards both in (In,Mn)Sb and (Ga,Mn)As. The anomalous-Hall coefficient shows a dramatic increase in the hysteresis loops in the ferromagnetic phase and an enhanced magnetization both below and above the phase transition. As the normal-Hall results suggest that the pressure does not change the carrier density [in (In,Mn)Sb] or rather decreases it [in (Ga,Mn)As], all the above observations are indicative of a pressure-induced enhancement of magnetic coupling. [source]

Exciton dynamics in quantum nano-structures of II,VI diluted magnetic semiconductors fabricated by electron-beam lithography

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2004
A. Uetake
Abstract Exciton dynamics in quantum dots (QDs) of II,VI diluted magnetic semiconductors (DMSs) has been studied by using an electron-beam lithography technique. The peak energy of excitonic photoluminescence in the QDs shows blue shifts up to 3.5 meV toward the dot diameter of 20 nm, indicating a lateral confinement effect for the exciton. The time-dependent energy shift of the exciton due to the localization is small as 2.9 meV, which originates from the suppression of the exciton diffusion due to the finite dot structure. The coupled QDs composed of a DMS magnetic well (MW) and a non-magnetic well (NW) were sucessfully fabricated, where the exciton energy in the NW was designed to be lower than that in the MW. The spin-polarized excitons migrate from the MW to the NW in magnetic fields and the exciton spin injection is demonstrated in the coupled QDs. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]