Search results for "Magnetic semiconductor"
showing 10 items of 31 documents
Stabilizing and increasing the magnetic moment of half-metals: The role of Li in half-HeuslerLiMnZ(Z=N,P,Si)
2015
Due to their similarities to metastable zinc-blende half-metals, we systematically examined the half-Heusler compounds $\ensuremath{\beta}\text{-LiMn}Z$ ($Z=\text{N},\text{P}$ and Si) for their electronic, magnetic, and stability properties at optimized lattice constants and strained lattice constants that exhibit half-metallic properties. We also report the other phases of the half-Heusler structure ($\ensuremath{\alpha}$ and $\ensuremath{\gamma}$ phases), but they are unlikely to be grown. The magnetic moments of these stable Li-based compounds are expected to reach as high as $4{\ensuremath{\mu}}_{\mathrm{B}}$ per unit cell when $Z=\text{Si}$ and $5{\ensuremath{\mu}}_{\mathrm{B}}$ per un…
Suppression of carrier induced ferromagnetism by composition and spin fluctuations in diluted magnetic semiconductors
2001
We suggest an approach to account for spatial (composition) and thermal fluctuations in "disordered" magnetic models (e.g. Heisenberg, Ising) with given spatial dependence of magnetic spin-spin interaction. Our approach is based on introduction of fluctuating molecular field (rather than mean field) acting between the spins. The distribution function of the above field is derived self-consistently. In general case this function is not Gaussian, latter asymptotics occurs only at sufficiently large spins (magnetic ions) concentrations $n_i$. Our approach permits to derive the equation for a critical temperature $T_c$ of ferromagnetic phase transition with respect to the above fluctuations. We…
Dephasing of orbital and spin degrees of freedom in semiconductor quantum dots due to phonons and magnons
2006
Phonon-induced decoherence of orbital degrees of freedom in quantum dots (QDs) (GaAs/InAs) is studied and the relevant time-scales are estimated versus dot dimension. Dephasing of excitons due to acoustic phonons and optical phonons, including enhancement of the effective Frohlich constant caused by localization, is assessed for the state-of-art QDs. Temporal inefficiency of Pauli blocking in QDs due to lattice inertia is additionally predicted. For QD placed in a diluted magnetic semiconductor medium a magnon induced dephasing of spin is estimated in accordance with experimental results for Zn(Mn)Se/CdSe. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Spintronics: a challenge for materials science and solid-state chemistry.
2007
Spintronics is a multidisciplinary field involving physics, chemistry, and engineering, and is a new research area for solid-state scientists. A variety of new materials must be found to satisfy different demands. The search for ferromagnetic semiconductors and stable half-metallic ferromagnets with Curie temperatures higher than room temperature remains a priority for solid-state chemistry. A general understanding of structure-property relationships is a necessary prerequisite for the design of new materials. In this Review, the most important developments in the field of spintronics are described from the point of view of materials science.
On the theory of domain structure in ferromagnetic phase of diluted magnetic semiconductors
2006
Abstract We present a comprehensive analysis of domain structure formation in ferromagnetic phase of diluted magnetic semiconductors (DMS) of p-type. Our analysis is carried out on the base of effective magnetic free energy of DMS calculated by us earlier [Yu.G. Semenov, V.A. Stephanovich, Phys. Rev. B 67 (2003) 195203]. This free energy, substituting DMS (a disordered magnet) by effective ordered substance, permits to apply the standard phenomenological approach to domain structure calculation. Using coupled system of Maxwell equations with those obtained by minimization of above free energy functional, we show the existence of critical ratio ν cr of concentration of charge carriers and ma…
Spin polarization in electrodeposited thin films of the molecule-based magnetic semiconductor Cr5.5(CN)12·11.5H2O
2013
The magnetoresistance (MR) effect of thin films of the Prussian Blue Analogue (PBA) Cr5.5(CN)12·11.5H2O, prepared by electrochemical deposition, has been measured using the standard two-point probe method. This molecule-based ferrimagnetic material, with a Tc = 240 K, exhibits MR up to 2% at 6 T and 200 K.
Effect of structural and compositional inhomogeneities on spin-glass transition in Hg1−x−yCrxMnySe crystals
2004
Abstract We report experimental results on the growth of Hg 1 −x−y Cr x Mn y Se crystals and their magnetic susceptibility χ ( T ) in dependence on the crystal structure and composition. It was found that the crystals with the Mn composition y =0.01–0.08 exhibit the spin-glass transition temperature T g =100–110 K. An increase of y value leads to the saturation of the χ max and T g characteristics in the composition ranges of y >0.06 and y >0.02, respectively. This phenomenon is explained as a result of phase-separated magnetic behavior caused by the formation of HgCr 2 Se 4 inclusions and textures.
X-ray absorption near edge spectroscopy at the Mn K-edge in highly homogeneous GaMnN diluted magnetic semiconductors
2006
We have studied by X-ray absorption spectroscopy the local environment of Mn in highly homogeneous Ga 1-x Mn x N (0.06 <x<0.14) thin epilayers grown by molecular beam epitaxy on [0001] SiC substrates. The measurements were performed in fluorescence mode around the Ga and Mn K-edges. In this report, we focus our attention to the X-ray absorption near edge spectroscopy (XANES) results. The comparison of the XANES spectra corresponding to the Ga and Mn edges indicates that Mn is substitutional to Ga in all samples studied. The XANES spectra measured at the Mn absorption edge shows in the near-edge region a double peak and a shoulder below the absorption edge and the main absorption peak after …
Optical Absorption of Zinc Selenide Doped with Cobalt (Zn1-xCoxSe) under Hydrostatic Pressure
2000
Optical absorption of the diluted magnetic semiconductor Zn 1-x Co x Se (x = 0.02) has been measured at room temperature under hydrostatic pressure up to 14 GPa in a membrane diamond-anvil cell. We found two absorption features: (i) an absorption structure in the energy range 1.5 to 1.8 eV, with a negligible pressure shift (i.e. (0.45 ± 0.05) meV/GPa) which we have identified as the Co 2+ (3d 7 ) internal transition 4 A 2 (F) → 4 T 1 (P) and (ii) an onset in the energy range 2 to 2.7 eV which redshifts with pressure (dE/dP = (-8.1 ± 0.6) meV/GPa). We have attributed such absorption edge to charge transfer between the ZnSe valence band and the Co 2+ (3d 7 ) levels. On the assumption that tho…
Optical absorption of zinc selenide doped with cobalt (Zn1−xCoxSe) under hydrostatic pressure
2000
Abstract The optical absorption of the diluted magnetic semiconductor Zn1−xCOxSe (x = 0.02) has been measured at room temperature under hydrostatic pressure up to 14GPa in a membrane diamond-anvil cell. We found two absorption features: (i) an absorption structure in the energy range 1.6−1.8eV, with a negligible pressure shift (i.e., 0.45 ± 0.05 meV/GPa) which we have identified as the Co2+(3d7) internal transition 4A2(F)→+4T1(P) and (ii) an onset in the energy range 2−2.7eV which redshifts with pressure (−8.1±0.6meV/GPa). We have attributed such absorption edge to charge transfer between the ZnSe valence band and the Co2+(3d7) levels.