Properties Of Magnetic Semiconductors Research Articles

Diluted magnetic semiconductor properties of Zn1 − x Cox O: 1 at% Al thin films prepared by pulsed DC magnetron sputtering

Zn1 − x CoxO: 1 at% Al(x = 0−0.3) films were grown on corning 7059 glass by asymmetrical bipolar pulsed dc magnetron sputtering. The c-axis orientation along the (002) plane was enhanced with increasing Co concentration. The ZnCoO thin films are grown to the fibrous grains of tight dome shape. The transmittance spectra showed that sp-d exchange interactions and typical d-d transitions become activated with increasing Co concentration. The electrical resistivity of ZnCoO films increased ranging from ∼10− 3 to ∼10−2 Ω ⋅ cm with increasing Co concentration, especially it increased greatly at 30 at% Co. X-ray photoelectron spectroscopy and alternating gradient magnetometer analyses indicated that no Co metal cluster in the ZnCoO films is formed and room temperature ferromagnetism is exhibited. These electrical and magnetic properties of ZnCoO films suggest a potential application of dilute magnetic semiconductor devices.

Effect of Light on the Magnetic Properties of Semiconductors

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Effect of Light on the Magnetic Properties of Semiconductors

Effect of Light on the Magnetic Properties of Semiconductors

Effect of hydrostatic pressure on the transport properties in magnetic semiconductors

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.

Investigations of multiphase states in vicinity of pressure‐induced phase transitions

AbstractIn the present work equations have been derived for thermomagnetic and galvanomagnetic effects of multiphase systems. The equations allow us to analyse complex thermal–electrical–magnetic properties of semiconductors under variation of concentration and configuration of inclusions. The results obtained make it possible, for example, to explain discrepancies between values of phase‐transition pressure determined from thermal, electrical, volumetric and other effects. A model developed has been applied for analysis of semiconductor–metal phase transitions. The approach offered allows us also to search for ways for improvement of thermoelectric and thermomagnetic effectiveness and figure of merit of complex semiconductor systems. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Elastic-strain mechanisms for the influence of temperature, magnetic field, and pressure on the resistive and magnetic properties of magnetic semiconductors

An analysis is made of the results of studies of the variation of the resistivity of a bulk polycrystalline sample of La0.56Ca0.24Mn1.2O3 under the influence of temperature (T), pressure (P), and magnetic field (H) and a study of the variation of the magnetostriction in single-crystal LaMnO3 as a function of T and H. It is found that the peaks of the magnetoresistive, baroresistive, and baromagnetoresistive effects occur at the same temperature, which is independent of magnetic field and pressure and corresponds to the temperature Tms of the metal–semiconductor phase transition in the absence of magnetic field and pressure. “Cooling” and “heating” effects of pressure and magnetic field are detected, and an equivalency of the influence of T, P, and H on the resistivity of the polycrystalline sample and of T and H on the magnetostriction of the single-crystal LaMnO3 is observed. The linearity of the shifts of the Tms(P) and Tms(H) peaks in the resistive properties of La0.56Ca0.24Mn1.2O3 is demonstrated and ...

Regularities in temperature, magnetic field and pressure effect on the resistive properties of magnetic semiconductors

The influence of hydrostatic pressure, magnetic field and temperature on resistivity behaviour of bulk and film samples La 0.9Mn 1.1O 3 and La 0.56Ca 0.24Mn 1.2O 3 at action of magnetic field and temperature has been analysed. It is established that the maximum of magnetoresistive and the revealed baroresistive, magnetobaroresistive effects coincide at the same temperature T pp. This temperature is equal to the “metal-semiconductor” phase transition temperature T ms. “Cooling” and “heating” effects of pressure and magnetic field have been revealed. A mutual correspondence of T– P– H (6.2 K, 1 kbar, 2.7 kOe) influence on polycrystalline sample La 0.9Mn 1.1O 3 resistivity has been determined. The linear change of T ms( P) and T ms( H) in La 0.9Mn 1.1O 3, La 0.56Ca 0.24Mn 1.2O 3 resistivity have been found. An importance of the regularities of elastic-deforming correspondence of T– H– P influence on magnetic, resistivity properties, phase transitions and effects was elucidated and explained. An alternating influence of T– H– P and its role in resistivity has been pointed. A correlation between structural, elastic and resistive properties is specified.

Characterization of high dose Fe implantation into p-GaN

High concentrations (3–5 at. %) of Fe were incorporated into p-GaN by direct implantation at elevated substrate temperature (350 °C). Subsequent annealing at 700 °C produced apparent ferromagnetic behavior up to ∼250 K for the 3 at. % sample. Selected area diffraction patterns did not reveal the presence of any other phases in the Fe-implanted region. The direct implantation process appears promising for examining the properties of magnetic semiconductors with application to magnetotransport and magneto-optical devices.

Electronic structure, growth, and structural and magnetic properties of magnetic semiconductor Fe/GaAs heterostructures

In this article we describe a study of the magnetic semiconductors of Fe/GaAs, undertaken theoretically and experimentally. We discuss the structural advantage of body-centered-cubic-Fe structure lattice matching to GaAs (001). Theoretical calculations using the self-consistent linear augmented-plane-wave method indicate the existence of an energy state of the quantum well in Fe layers in a GaAs/Fe/GaAs double heterostructure. We then present the preparation of Fe/GaAs heterostructures by using molecular beam epitaxy. α-Fe and δ-Fe could be grown epitaxially on (001) GaAs at a substrate temperature of 290 and 580 °C, respectively, which was confirmed from the results of reflection high energy electron diffraction and x-ray diffraction measurements. We also found that, in order to obtain α-Fe/GaAs, a low-temperature GaAs growth must be induced before the Fe growth can occur. Differences in magnetic properties were observed in the magnetic measurements, indicating that α-Fe dominates the ferromagnetic state, while the δ-Fe shows relatively slight ferromagnetic behavior.

Magnetic and transport properties of III–V based magnetic semiconductor (GaMn)As: Growth condition dependence

We have studied growth condition dependence of magnetic and transport properties of magnetic semiconductor (GaMn)As grown by low-temperature molecular-beam epitaxy (LT-MBE). With increasing substrate temperature and decreasing As overpressure during the growth of (Ga1−xMnx)As with x=0.043, the hole concentration increased, the conduction behavior changed from semiconducting to metallic, and the ferromagnetic transition temperature became higher. This is explained by a decrease in the compensation of Mn acceptors by the reduction of excess As related defects in the LT-MBE grown (GaMn)As. Our experimental results indicate that the selection of the MBE growth parameters is very important for better controlling the electronic and magnetic properties of (GaMn)As.

The changes in electronic structure and optical properties of magnetic semiconductors at magnetic phase transitions

Abstract The influence of magnetic phase transitions on electronic structure and optical properties of magnetic semiconductors is discussed. Europium chalcogenides and chromium chalcogenide spinels are the main subjects of the investigation. It is shown, that many-body effects are responsible for the changes of optical properties and non-rigid band behavior of electronic structure. Magnetic phase transition leads to energy shift of wide bands and change in density of states of “magnetic” d(f)-electrons without any significant shift of their energies. The influence of fluctuations at T ∼ T c and antiferromagnetic semiconductors are also considered.

Effects of spin ordering on phonon and plasmon spectra, and dielectric properties in magnetic semiconductors

Abstract Effects of spin ordering on the phonons, plasmons, and dielectric properties have been investigated for many magnetic crystals, such as Cr-spinels, EuX (X = O, S, Se, Te), and fluorite-type compounds. Of these phenomena, the static dielectric constant and Raman scattering have been extensively discussed. However, the dielectric parameters obtained from infrared spectra have not been discussed in spite of observed various phenomena arising from the direct coupling of spin system with phonons or electrons. Furthermore, these microscopic phenomena can be combined with the macroscopic dielectric values with respect to the spin ordering effect. It will ascertain the mechanism of the spin ordering effect on the values. From this point of view, we review the spin-dependent phenomena on the frequencies of TO and LO phonon modes, phonon damping, optical and static dielectric constants, effective charge, and also on plasmon parameters in the spinel type magnetic semiconductors.

Transport properties of magnetic semiconductors: The weak coupling situation

We examine the consequences for the transport properties of the exchange interaction between carriers in a relatively wide band and localized magnetic moments, with special reference to the properties of europium compounds. In section 2, the model of indirect exchange will be recalled. In section 3, the variation of carrier mobility with temperature and magnetic field will be studied, including (i) the spin-disorder scattering which leads to critical resistance and to negative magnetoresistance and (ii) the modifications in other scattering mechanisms which arise from the exchange interaction. We will analyze in section 4 how the exchange interaction induces or enhances the localization of a carrier around a charged impurity, leading to a magnetization dependence of the conductivity activation energy. Finally, in section 5, the role of magnetic disorder in the conduction process will be discussed. Throughout this review, the role played by non-diagonal linear response functions (e.g., response of the electronic system to magnetic field perturbations) will be emphasized.

Two-electron bond-orbital model I

Harrison's one-electron bond-orbital model of tetrahedrally coordinated solids is generalized to a two-electron model, using an extension of the method of Falicov and Harris for treating the hydrogen molecule. The six eigenvalues and eigenstates of the two-electron anion-cation Hamiltonian entering this theory can be found exactly even in the most general case. In this first paper, however, the nonorthogonality of the anion and cation $s{p}^{3}$ hybrids is neglected to simplify the treatment and to emphasize the most essential features of the model. The two-electron formalism is shown to provide a useful basis for calculating both nonmagnetic and magnetic properties of semiconductors in perturbation theory. As an example of the former, we calculate expressions for the electric susceptibility and the dielectric constant. In the limit of no electron correlation, our expression for the susceptibility agrees with that found by Harrison and by Harrison and Ciraci. As an example of the latter, we calculate new expressions for the nuclear exchange and pseudodipolar coefficients. A simple theoretical relationship between the dielectric constant and the exchange coefficient is also found in the limit of no correlation. The expressions for the exchange and pseudodipolar coefficients are quantitatively evaluated in the limit of no correlation for twenty elemental and binary semiconductors, and the results are compared with existing experimental data. Preliminary studies on the quantitative effects of correlation on the various quantities considered here are also discussed.

Ferromagnetic and antiferromagnetic semiconductors

A review is given of the experimental and theoretical data on ferromagnetic and antiferromagnetic semiconductors. Information on the magnetic, electrical, and optical properties is analyzed systematically. The main theoretical ideas on the physics of magnetic semiconductors are given without detailed proof and are used in the interpretation of the experimental results relating to the influence of the magnetic order on the electrical and optical properties of magnetic semiconductors and to the influence of conduction electrons on the magnetic order.

Band Structure of Magnetic Semiconductors

A method is proposed for representing the effective one-electron density-of-states of materials in which some of the valence electrons are extremely localized. If some additional rules regarding nonconducting states and occupation-number dependent states are imposed, this scheme can be used to interpret both the electrical and optical properties of magnetic semiconductors. The materials NiO and CoO are discussed in detail.