Magnetic susceptibility of liquid semiconductors

The temperature dependence of the magnetic susceptibility of semiconducting ZnSb, CdGeAs₂ and CdSnAs₂ is studied in the vicinity of the melting point. It is shown that the susceptibility change at the melting point cannot be quantitatively explained only by the susceptibility of the electron gas present in the melt, but one must take into account other components connected with the susceptibility of the lattice. A quantitative guess of the susceptibility of molten semiconductors that were not yet measured is given.     

Magnetic susceptibility of multinary diamondlike semiconductors

Summary The magnetic susceptibility of some A^IB ₂ ^II C^IIIX ₄ ^VI (A^I=Cu, Ag; B^II=Zn, Cd; C^III=Ga, In; X^VI=Se, Te) diamondlike chalcogenides has been measured at RT. Coherently with the form of the relative A^IC^IIIX ₂ ^VI -B^IIX^VI phase diagrams, their magnetic susceptibility fulfils the sum rule typical of ideal solid solutions. Separate values of the diamagnetic and paramagnetic contributions to total magnetic susceptibility are reported and discussed according to a chemical-bond approach previously described. Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

Magnetic susceptibility in a layered superlattice

Paramagnetic and diamagnetic contributions to the magnetic susceptibility are calculated for a layered superlattice as a function of the temperature in both degenerate and nondegenerate regimes. The susceptibility shows distinctly different temperature dependences as the inter-layer bandwidth as well as the Fermi energy is varied from a two-dimensional to a three-dimensional regime, thus giving valuable information about the electron density and the inter-layer tunneling.     

Magnetic semiconductors

As far as the electrical conductivity is concerned, solids are usually classified as metals, semiconductors, or insulators. In metals the concentration of the charge carriers responsible for the electrical conductivity is large, whereas in semiconductors and insulators the carrier concentration is much smaller. The distinction between semiconductors and insulators is based on a difference in the nature of the conductivity. For semiconductors the charge carriers (electrons or holes) occupy the states of energy bands; these states are not Iocalized on particular atoms, but spread throughout the entire crystal. In such a situation the mobility of the carriers can be quite high and would, in fact, be infinite in a rigid periodic lattice; in this model the thermal motion of the atoms induces a scattering of the carriers and thus limits the conductivity to finite values. The classical examples of semiconductors are the elements Si and Ge and compounds such as GaAs, InSb, CdTe, ZnS, etc.     

Na adsorption on the layered semiconductors SnS2 and WSe2

The interaction of Na metal deposits with UHV cleaved van der Waals surfaces (0001) of SnS₂ and WSe₂ was investigated with SXPS and LEED. For SnS₂ an insertion reaction (intercalation) of Na leads to a reduced Sn-species. For WSe₂“non-reactive” intercalation occurs at room temperature which follows the rigid band model. At 120 K a metallic Na overlayer is formed. The observed reactivity is discussed in terms of bulk thermodynamics and the obtained difference is tentatively related to differences in the electronic structure of the compounds.     

Magnetic properties of TlCoS2 and TlCoSe2 layered compounds

The TlCoS₂ and TlCoSe₂ compounds are synthesized and their magnetic properties are studied in the temperature range 77–300 K. It is established on the basis of x-ray diffraction analysis that these compounds possess a hexagonal structure. Examination of the magnetization and paramagnetic susceptibility has shown that TlCoS₂ and TlCoSe₂ are ferrimagnets. The Curie temperature for TlCoS₂ is equal to 112 K, and T _C for TlCoSe₂ is less than 77 K. The effective magnetic moments are equal to 4.6 μ_B (TlCoS₂) and 4.85 μ_B (TlCoSe₂) and agree well with the theoretical values. __________ Translated from Fizika Tverdogo Tela, Vol. 42, No. 8, 2000, pp. 1449–1450. Original Russian Text Copyright ? 2000 by Sadykhov, Kerimova, Asadov, Veliev.     

Magnetic susceptibility of the rare earth element impurities in the IV-VI semiconductors and Curie-Weiss law

Peculiarities of applying the Curie-Weiss law to the analysis of the magnetic susceptibility of the impurities of the rare earth elements in the IV-VI crystals are examined. It is shown that the traditional approach to the determination of the paramagnetic Curie temperature of ferromagnets and antiferromagnets applied to the impurities of ferromagnetic and antiferromagnetic elements in the doped crystal may lead to fundamental mistakes. The results of this examination are used to analyze the high temperature magnetic susceptibility of Eu and Gd impurities in the PbTe doped crystals grown from the melt using the Bridgman method. It is established that the doping of PbTe with Eu leads to the formation of ferromagnetic inclusions and the same doping with Gd leads to the formation of antiferromagnetic inclusions in the crystal. It is shown that these inclusions are most likely the complexes based on the europium or gadolinium oxides EuO and Gd₂O₃, respectively.     

Magnetic properties of ZrO2-diluted magnetic semiconductors

Monoclinic zirconia (ZrO₂) as a potential host for diluted magnetic semiconductors (DMS) was investigated using density functional theory (DFT). Our calculations assessed the feasibility of long-range magnetic order at room temperature for transition metal ions substituting Zr. The defect-related d states split into e_g and t_2g bands. The exchange mechanism was shown to have strong nearest-neighbour coupling for several dopants reaching up to 150 meV for Fe. However, there was little to no long-range coupling extending beyond nearest-neighbour coordination, resulting in a non-physically high-defect concentration necessary for room temperature ferromagnetism.     

Magnetic phase diagram of layered cobalt dioxide LixCoO2

The magnetism of LixCoO2 (LCO), which has a similar structure to NaxCoO2 (NCO), has been investigated by muon-spin spectroscopy and susceptibility measurements using samples with x=0.1-1 prepared by an electrochemical reaction. In the x range below 0.75, LCO was found to be Pauli paramagnetic down to 1.8 K, suggesting an intermediate- or weak-coupling regime, although disordered local moments, with volume fractions below approximately 20%, appear at low T for LCO with x > or = 0.5. The phase diagram and interactions of LCO are thus strikingly different from NCO, while the differences cannot be explained simply by structural differences between the two systems.     

Thermal conductivity of GaS and GaSe layered semiconductors

This paper reports on the results of experimental investigations into the thermal conductivity of GaS and GaSe layered semiconductor crystals in directions parallel and perpendicular to the crystal layers in the temperature range 5–300 K. Specific features of the thermal conductivity of these crystals are analyzed.     

Magnetic excitations in ferromagnetic semiconductors

Magnetic excitations in a series of GaMnAs ferromagnetic semiconductor films were studied by ferromagnetic resonance (FMR). Using the FMR approach, multi-mode spin wave resonance spectra have been observed, whose analysis provides information on magnetic anisotropy (including surface anisotropy), distribution of magnetization precession within the GaMnAs film, dynamic surface spin pinning (derived from surface anisotropy), and the value of exchange stiffness constant D. These studies illustrate a combination of magnetism and semiconductor physics that is unique to magnetic semiconductors.     

Magnetic properties of diluted magnetic semiconductors

A review will be given of the magnetic characteristics of diluted magnetic semiconductors and the relation with the driving exchange mechanisms. II–VI as well as IV–VI compounds will be considered. The relevance of the long-range interaction and the role of the carrier concentration will be emphasized.     

Temperature dependence of absorption edge anisotropy in 2H- MoSe2 layered semiconductors

The absorption-edge anisotropy of 2H- MoSe₂ was studied by photoconductivity (PC) measurements as a function of temperature in the range of 12-300 K. A significant shift towards lower energies has been observed in the PC spectra on the edge plane with respect to those corresponding to the van der Waals (VdW) plane. The parameters that describe the temperature dependence of the absorption edges are evaluated by the Bose-Einstein empirical expression. Effective phonon energy was estimated from the temperature dependence of the Urbach energy. The estimated effective phonon energy for the VdW and edge planes, respectively, can be correlated to the observed Raman active and modes.     

Magnetic quenching of positronium in semiconductors

The positronium-determined characteristics of electron-positron annihilation in semiconductors in the presence of an external magnetic field are calculated. It is assumed that the positronium atoms can be in one of two states, delocalized or localized (at defects), and undergo not only pick-off annihilation but also orthoparaconversion (³S₁ ¹S₀) on free carriers. Numerical calculations were made for a field H=15 kG. The field has very different effects on localized and delocalized positronium, and in the first case the effect depends strongly on the nature of the defect.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No.11, pp. 75–78, November, 1980.     

Tunable electronic behavior in 3d transition metal doped 2H-WSe2

Structural and electronic properties of 3d transition metal Sc, Ti, Cr and Mn incorporated 2H-WSe₂ have been systematically investigated by first-principles calculations based on density functional theory. The calculated formation energies reveal that all the doped systems are thermodynamically more favorable under Se-rich condition than W-rich condition. The geometry structures almost hold that of the pristine 2H-WSe₂ albeit with slight lattice distortion. More importantly, the electronic properties have been significantly tuned by the dopants, i.e., metal and semimetal behavior has been found in Sc, Ti and Mn-doped 2H-WSe₂, respectively, semiconducting nature with narrowed band gap is expected in Cr-doped case, just as that of the pristine 2H-WSe₂. In particular, magnetic character is realized by incorporation of Mn impurity with a total magnetic moment of 0.96 μ_B. Our results suggest chemical doping is an effective way to precisely tailor the electronic structure of layered transition metal dichalcogenide 2H-WSe₂ for target technological applications.     

Magnetic properties of co-doped SnO2 diluted magnetic semiconductors

Polycrystalline samples of Sn_1−xCo_xO₂ are prepared for x=0.02, 0.05 and 0.10. They all exhibit room temperature ferromagnetism with decrease in saturation magnetization with increase in doping. The magnetization data recorded at 85 K, 295 K and 400 K for x ≥ 0.05 could be analyzed in terms of bound magnetic polaron model and the typical polaron concentration at room temperature is found to be in the order of 10²¹ per m⁻³.     

Magnetic percolation in diluted magnetic semiconductors

We demonstrate that the magnetic properties of diluted magnetic semiconductors are dominated by short ranged interatomic exchange interactions that have a strong directional dependence. By combining first principles calculations of interatomic exchange interactions with a classical Heisenberg model and Monte Carlo simulations, we reproduce the observed critical temperatures of a broad range of diluted magnetic semiconductors. We also show that agreement between theory and experiment is obtained only when the magnetic atoms are randomly positioned. This suggests that the ordering of diluted magnetic semiconductors is heavily influenced by magnetic percolation, and that the measured critical temperatures should be very sensitive to details in the sample preparation, in agreement with observations.     

Exciton susceptibility of semiconductors at high laser-excitation levels

The hysteresis behavior of the real and imaginary parts of the susceptibility of a semiconductor in the exciton region of the spectrum is investigated with consideration of the exciton-phonon and elastic exciton-exciton interactions in the pump-probe regime as a function of the intensity and frequency of the strong laser pulse and the frequency of the probe pulse. The conditions for the appearance of suppression of the damping and amplification of the probe pulse are determined. Abrupt red and blue shifts of the spectral position of the exciton absorption band as a function of the pump pulse intensity are predicted. Fiz. Tverd. Tela (St. Petersburg) 40, 934–935 (May 1998)