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Lead telluride and germanium telluride are well-known IV-VI semiconductors, which is now the focus of research due to the perspective of application as thermoelectrics for midrange temperatures. Solid solutions and heterostructures on this basis, obtained by molecular beam epitaxy, are a promising direction for the development of these materials. In this paper, we have focused on the Raman spectra excited by the 514.5 nm laser line (out of resonance) of PbTe, GeTe, (Pb, Ge)Te, and (Pb, Ge, Eu)Te layers grown on BaF2 (111) monocrystalline substrates. The obtained phonon properties are related to the properties of the corresponding bulk materials or can be explained by a model that takes into account the difference in the masses of the constituent elements only, as is the case with the local mode of Ge in PbTe (registered at about 181 cm−1). Multiphonon processes registered for this phonon are a consequence of the change in the electronic structure of PbTe and electron-phonon interaction. An improvement in the quality of thin films due to doping with Eu ions was also registered. [ABSTRACT FROM AUTHOR]

We present studies of structural, magnetic, and electrical properties of Zn1-x-y CdxMnyGeAs2 nanocomposite ferromagnetic semiconductor samples with changeable chemical composition. The presence of MnAs clusters induces the studied alloy room temperature ferromagnetism with the Curie temperature, TC, around 305?K. The chemical composition of the chalcopyrite matrix controls the geometrical parameters of the clusters, inducing different magnetoresistance effects in the crystals. The presence of ferromagnetic clusters in the alloy induces either negative or positive magnetoresistance with different values. The Cd-content allows a change of magnetoresistance sign in our samples from negative (for x ≈ 0.85 ) to positive (for x ≈ 0.12 ). The negative magnetoresistance present in the samples with x≈0.85 is observed at temperatures T<25 ?K with maximum values of about -32% at T = 1.4 ?K and B = 13 T, strongly depending on the Mn content, y. The positive magnetoresistance present in the samples with x ≈ 0.12 is observed with maximum values not exceeding 50% at B = 13?T and T = 4.3 ?K, changing with the Mn content, y. [ABSTRACT FROM AUTHOR]

Magnetic and transport properties of Ge1-x-yMnxEuyTe crystals with chemical compositions 0.041⩽x⩽0.092 and 0.010⩽y⩽0.043 are studied. Ferromagnetic order is observed at 150C, where TC is the Curie temperature, with coefficients RS independent of temperature. The scaling analysis of the AHE leads to a conclusion that this effect is due to a skew scattering mechanism. [ABSTRACT FROM AUTHOR]

Positron annihilation spectroscopy is used to study point defects in Zn1-xMnxGeAs2 crystals with low Mn content 0 ≤ χ ≤ 0:042 with disordered zincblende and chalcopyrite structure. The role of negatively charged vacancies and non-open-volume defects is discussed with respect to the high p-type conductivity with carrier concentration 1019 ≤ p ≤ 1021 cm-3 in our samples. Neutral As vacancies, together with negatively charged Zn vacancies and non-open-volume defects with concentrations around 1016 - 1018 cm-3, are observed to increase with increasing Mn content in the alloy. The observed concentrations of defects are not sufficient to be responsible for the strong p-type conductivity of our crystals. Therefore, we suggest that other types of defects, such as extended defects, have a strong influence on the conductivity of Zn1-xMnxGeAs2 crystals. [ABSTRACT FROM AUTHOR]

We present the studies of structural, electrical, and magnetic properties of bulk Cd1-xMnxGeAs2 crystals with low Mn content, x, varying from 0 to 0.037. The studied samples have excellent crystallographic quality indicated by the presence of diffraction patterns never before observed experimentally for this compound. The electrical transport in our samples is dominated by thermal activation of conducting holes from the impurity states to the valence band with activation energy of about 200 meV. The defect states acting as ionic scattering centers with concentration in the range from 6 to 15 × 1017 cm-3 are observed. The effective Mn content in our samples, xθ, determined from fit of the susceptibility data to the Curie-Weiss law, is very close to the average chemical content, x. It indicates that the Mn ions are distributed randomly, substituting the Cd sites in the host CdGeAs2 lattice. We observe a negative Curie-Weiss temperature, ∣θ∣ ⩽ 3:1K, increasing as a function of x. This indicates the significance of the short-range interactions between the Mn ions. © 2014 AIP Publishing LLC. [ABSTRACT FROM AUTHOR]

Magnetotransport properties of spin-glass-like Ge1-x-ySnxMnyTe mixed crystals with chemical composition changing in the range of 0.083≤x≤0.142 and 0.012≤y≤0.119 are presented. The observed negative magnetoresistance we attribute to two mechanisms, i.e., weak localization occurring at low fields and spin disorder scattering giving contribution mainly at higher magnetic fields. A pronounced hysteretic anomalous Hall effect (AHE) was observed. The estimated AHE coefficient shows a small temperature dependence and is dependent on Mn-content, with changes in the range of 10-7S<10-6m3/C. The scaling law analysis has proven that the AHE in this system is due to the extrinsic mechanisms, mainly due to the skew scattering accompanied with the side jump processes. [ABSTRACT FROM AUTHOR]

We present the studies of magnetic properties of Ge1-xCrxTe diluted magnetic semiconductor with changeable chemical composition 0.016≤x≤0.061. A spin-glass state (at T≤35 K) for x = 0.016 and 0.025 and a ferromagnetic phase (at T<60 K) for x≥0.030 are observed. The long range carrier-mediated magnetic interactions are found to be responsible for the observed magnetic ordering for x<0.045, while for x≥0.045 the spinodal decomposition of Cr ions leads to a maximum and decrease of the Curie temperature, TC, with increasing x. The calculations based on spin waves model are able to reproduce the observed magnetic properties at a homogeneous limit of Cr alloying, e.g., x<0.04, and prove that carrier mediated Ruderman-Kittel-Kasuya-Yosida interaction is responsible for the observed magnetic states. The value of the Cr-hole exchange integral, Jpd, estimated via fitting of the experimental results with the theoretical model, is in the limits 0.77...0.88 eV. [ABSTRACT FROM AUTHOR]

We present systematic studies of magnetic and transport properties of Zn1-xMnxGeAs2 semimagnetic semiconductor with the chemical composition varying between 0.053≤x≤0.182. The transport characterization showed that all investigated samples had p-type conductivity strongly depending on the chemical composition of the alloy. The Hall effect measurements revealed carrier concentrations p≥1019 cm-3 and relatively low mobilities, μ≤15 cm2/(V s), also chemical composition dependent. The magnetic investigations showed the presence of paramagnet-ferromagnet phase transitions with transition temperatures greater than 300 K for the samples with x≥0.078. We prove by means of x-ray diffraction, nuclear magnetic resonance, and scanning electron microscopy techniques that the observed room temperature ferromagnetism is due to the presence of MnAs inclusions. The high field magnetoresistance showed the presence of giant magnetoresistance effect with maximum amplitudes around 50% due to the presence of nanosize ferromagnetic grains. [ABSTRACT FROM AUTHOR]

We have studied vacancy defects in chalcopyrite semimagnetic semiconducting mixed Zn1-x(Mn,Co)xGeAs2 bulk crystals with alloy composition x varying between 0.052 to 0.182 using positron annihilation spectroscopy. We identified As vacancies, potentially complexed with the transition metal alloying elements, in all the studied samples, while no cation vacancy related defects were detected. The positron lifetimes for the bulk ZnGeAs2 lattice and neutral As vacancy were determined to be τB=220–230 ps and τAs=300±10 ps, respectively. Our results also show that the p-type conductivity in the samples is not due to cation vacancy related acceptor centers. The As vacancies were found to be present at such low concentrations that they cannot be responsible for the compensation of the p-type conductivity or the reduction of mobility in the Zn1-x(Mn,Co)xGeAs2 samples. [ABSTRACT FROM AUTHOR]

We present studies of magnetic and transport properties of Ge1-x-ySnxMnyTe mixed crystals with chemical compositions 0.083¿x¿0.142 and 0.012¿y¿0.119. The transport characterization measurements were performed at temperatures 4.2<300 K. The results showed feature characteristic for narrow gap semiconductors, e.g., metallic conductivity with pxx¿10-4 ¿ cm and hole concentrations p>1021 cm-3. It was found that the transport properties strongly depend on the chemical composition of the alloy. The magnetic investigations included measurements of linear ¿1 and harmonic ¿2,3 ac susceptibilities as a function of temperature and of the applied magnetic field amplitude and frequency. Qualitative analysis of our experimental data showed that in the studied system, in the investigated composition range, the spin glass order exists at temperatures up to 50 K. [ABSTRACT FROM AUTHOR]

Magnetization dynamics of a single-domain ferromagnet is studied theoretically using the methods developed for self-organization phenomena. Time evolution of the magnetization is described by the Landau-Lifshitz-Gilbert equation with the spin-transfer torque included. The equilibrium and stationary states are investigated as a function of spin current and external magnetic field. The presented bifurcation diagram allows the margins of a neutral stability mode of the equilibrium and stationary states to be determined. An envelope equation for the magnetization switching is derived. The switching time Δτ between different states is found to be comparable to the half-width of the time derivative of the system energy, which allows the energy flow due to spin current and the magnetization switching velocity to be related. Dynamics of the phase states in external magnetic field and in the presence of spin current is analyzed using different methods of numerical analysis. [ABSTRACT FROM AUTHOR]

Structural investigation of as-grown as well as annealed Ga[sub 1-x]Mn[sub x]As epilayers was carried out using high-resolution x-ray diffraction (XRD) measurements for a wide range of Mn concentrations (0.027<=x<=0.083), with special attention on how the interstitial Mn atoms (Mn[sub I]) influence the lattice parameter of this material. We observe a distinct decrease of the lattice parameter after low-temperature annealing of Ga[sub 1-x]Mn[sub x]As, which is known to reduce the Mn[sub I] concentration. The reciprocal space maps measured for all of the investigated samples showed that the Ga[sub 1-x]Mn[sub x]As layers are fully strained—i.e., they remain pseudomorphic to the GaAs (001) substrate—for the entire thickness of the samples used (in the present case over 100 nm). In all cases studied, the XRD measurements revealed high crystalline perfection of both as-grown as well as annealed Ga[sub 1-x]Mn[sub x]As epilayers. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The AC magnetic susceptibility in the range 5-130 K of the tellurite glass systems: TeO2-MnO2-ZnO-PbO and TeO2-MnO2-V2O5-Fe2O3 was measured and analyzed. The investigations of the AC magnetic susceptibility facilitated the determination of the molar susceptibility, paramagnetic magnetic susceptibility, paramagnetic Curie temperature, and magnetic entropy changes of the tellurite glasses. The results clarified that the temperature dependence of the magnetic susceptibility deviated from the Curie law and the increase of the small negative values of Curie temperature indicated negative interchange interactions between the antiferromagnetically coupled manganese ions within the present glass network. The magnetic moments evaluated from susceptibility measurements of the glasses show the predominance of the Mn2+ valence state than Mn3+ valence state of MnO2. [ABSTRACT FROM AUTHOR]

Abstract: The phase changes of MnO nanoparticles under laser‐induced heating have been studied. Previous confirmation of the existence of MnO phase was based on the X‐ray diffraction measurements. Here, we report the experimental spectra of nonresonant Raman scattering in the range between 100 and 1,600 cm−1, for a sample irradiated with 8 different laser powers. The laser‐induced heating has produced change in existing phases in sample, destruction of MnO phase, and creation of MnO2, Mn3O4, and MnOOH phases along with formation of Mn2+ on the sample surface. These phase changes have been confirmed by X‐ray diffraction and atomic force microscopy measurements. [ABSTRACT FROM AUTHOR]

We present the results of structural characterization of Cd1 − xMn xGeAs2 chalcopyrite-type crystals with low Mn content x varying from 0 to 0.037. High resolution X-ray powder diffraction method of measurements and Rietveld refinements procedure used for analysis of obtained diffraction patterns revealed high crystal quality of the samples. The substitutional alloying of Cd1 − xMn xGeAs2, with Mn ions at Cd sites, has been confirmed. The analytical equations describing the linear reduction of the lattice parameters with increase of Mn content were deduced and compared with the literature results of theoretically estimated lattice parameters of compounds of the same kind. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We present the studies of structural, electrical and magnetic properties of bulk Sn1−x−y PbxCryTe mixed crystals with chemical composition 0.18 ⩽ x ⩽ 0.35 and 0.007 ⩽ y ⩽ 0.071. The magnetometric studies indicate that for the high Cr-content, y = 0.071, the alloy shows ferromagnetic alignment with the Curie temperature, TC, around 265 K. The Cr5Te8 clusters are responsible for the ferromagnetic order. At low Cr content, y = 0.01, a peak in the ac magnetic susceptibility identified as the cluster-glass-like transition is observed at a temperature about 130 K. The cluster-glass-like transition is likely due to the presence of Cr2Te3 clusters in the samples with y ≈ 0.01. The transport characterization of the samples indicated strong metallic p-type conductivity with relatively high carrier concentration, n > 1020 cm−3, and carrier mobility, μ > 150 cm2/(V s). [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the magnetotransport properties of the Ge0.743Pb0.183Mn0.074Te mixed crystal. The results of magnetization measurements indicated that the compound is a spin-glass-like diluted magnetic semiconductor with critical temperature TSG = 97.5 K. Nanoclusters in the sample are observed. Both, matrix and clusters are magnetically active. Resistivity as a function of temperature has a minimum at 30 K. Below the minimum a variable-range hopping is observed, while above the minimum a metallic-like behavior occurs. The crystal has high hole concentration, p = 6.6×1020 cm-3, temperature-independent. Magnetoresistance amplitude changes from –0.78 to 1.18% with increase of temperature. In the magnetotransport measurements we observed the anomalous Hall effect with hysteresis loops. Calculated anomalous Hall effect coeffcient, RS = 2.0 × 106 m3/C, is temperature independent. The analysis indicates the extrinsic skew scattering mechanism to be the main physical mechanism responsible for anomalous Hall effect in Ge0.743Pb0.183Mn0.074Te alloy. [ABSTRACT FROM AUTHOR]

We present the studies of Sn1-xCrxTe semimagnetic semiconductors with chemical composition x ranging from 0.004 to 0.012. The structural characterization indicates that even at low average Cr-content x ⩽ 0:012, the aggregation into micrometer size clusters appears in our samples. The magnetic properties are affected by the presence of clusters. In all our samples we observe the transition into the ordered state at temperatures between 130 and 140 K. The analysis of both static and dynamic magnetic susceptibility data indicates that the spin-glass-like state is observed in our samples. The addition of Cr to the alloy seems to shift the spin-glass-like transition from 130 K for x = 0:004 to 140 K for x = 0:012. [ABSTRACT FROM AUTHOR]

The results of investigation of structural and electrical properties of bulk SiC crystals, which were grown by physical vapor transport method with different Ce impurity content added to the SiC source material, are presented. The gradual dosage of cerium from the SiC source and continuous presence of the cerium vapor over the SiC crystallization fronts during the crystal growth processes are confirmed. The cerium influences the overall concentration of structural defects. The increase of the concentration of both, donors and acceptors, and appearance of new shallow donors (15-32 meV) in 4H-SiC crystals are observed. [ABSTRACT FROM AUTHOR]

We present the experimental evidence for the presence of spinodal decomposition of the magnetic ions in the Ge1-x-yCrxEuyTe samples with chemical composition varying in the range of 0:015 ⩽ x ⩽ 0:057 and 0:003 ⩽ y ⩽ 0:042. The ferromagnetic transition at temperatures 50 ⩽ T ⩽ 57 K was observed, independent of the chemical composition. The long-range carrier mediated itinerant magnetic interactions seem to be responsible for the observed ferromagnetic order. The magnetic irreversibility with coercive field HC = 5-63 mT and the saturation magnetization MS ≈ 2-6 emu/g are found to strongly depend on the chemical composition of the alloy. [ABSTRACT FROM AUTHOR]

We present a detailed study of layered semiconductor InSe doped with Mn. X-ray and neutron diffraction analyses of (In,Mn)Se single crystals show the presence of a main phase as In1-xMnx solid solution, the second antiferromagnetic MnSe phase, and traces of In4Se3. Magnetic measurements reveal ferromagnetic behavior of (In,Mn)Se with the Curie temperature about 800 K. The ferromagnetic cluster model and exchange interaction via 2D electron gas, as the reasons of spontaneous magnetization, are discussed. The dramatic transformation of (In,Mn)Se electron spin resonance (ESR) spectra as a function of temperature is revealed. At the magnetic field perpendicular to crystallographic c axis, a low-field line within the temperature range 70 down to 4.7 K is observed. It shifts to smaller magnetic fields with temperature decrease. Neutron diffraction studies reveal the strong rise for one of the reflection peaks with temperature decrease in the same temperature region where ESR spectra transformation occurs. This peak corresponds to double MnSe interplanar distance in the [111] direction what is a period of its magnetic lattice. Magnetic structure of (In,Mn)Se single crystal is discussed. [ABSTRACT FROM AUTHOR]

Transport and magnetic properties of the IV-VI ferromagnetic multinary, mixed compounds Get-xMnx,Te, Get-x-yMnxEuyTe and Ge1-x-yMn,xYbyTe (0.045 ≤ x <≤ 0.47, y < 0.04) were investigated in magnetic fields up to 13 T and in the temperature range 1.6-300 K. The Curie temperatures of studied samples exceed 100 K. Based on the dependences of the Hall resistivity and magnetization on magnetic field, the anomalous Hall coefficients Rs were calculated, and Rs dependences on crystal composition and temperature were found. [ABSTRACT FROM AUTHOR]

Thermoelectric power, electrical conductivity, and high field Hall effect were studied over a broad temperature range in ferromagnetic Ga1-xMnxAs epitaxial layers (0.015 ≤ x ≤ 0.06). Thermoelectric power analysis gives information about carrier transport mechanisms in layers with both metallic and non-metallic types of conductivity and allows determination of the Fermi energy and carrier concentration. At high temperatures (T > 70 K), the thermoelectric power in GaMnAs linearly increases with increasing temperature. That indicates the presence of a degenerate hole gas with the Fermi energy EF = 220 ± 25 meV, nearly independent of Mn content (for 0.02 ≤ x ≤ 0.05). At lower temperatures, GaMnAs layers with metallic-type conductivity show an additional contribution to the thermoelectric power with the maximum close to the Curie temperature. [ABSTRACT FROM AUTHOR]

Simple magnetoresistive nanodevices formed by narrow constrictions of submicron width in the epitaxial film of a ferromagnetic (Ga,Mn)As semiconductor have been fabricated employing the electronbeam-lithography patterning and low-energy low-dose oxygen ion implantation. Low-temperature charge-carrier transport through the constrictions has been investigated and correlated with magnetic properties the film. The constricted devices revealed abrupt jumps of a reduced resistance that appeared when the sweeping magnetic field crossed the regions of the coercive field of the film magnetization. In contrast, the non-constricted reference device displayed abrupt jumps of an enhanced resistance at the same values magnetic field. We interpret the both features, whose positions on the magnetic-field scale reflect the hysteresis loop of magnetization, as manifestation of domain wall contribution to the (Ga,Mn)As film resistance. Presumably, the suppression of the weak localization effects by a domain wall located at the constriction results in a negative contribution of a domain wall to the resistance, while the spin-orbit interaction can be responsible for its positive contribution to the resistance. [ABSTRACT FROM AUTHOR]

In (Eu,Gd)Te semiconductor alloys, a well known antiferromagnetic semiconductor compound EuTe is transformed into an n-type ferromagnetic alloy. This effect is driven by the RKKY interaction via conducting electrons, created due to the substitution of Gd3+ for Eu2+ ions. It is expected that due to the high degree of electron spin polarization, (Eu,Gd)Te can be exploited in new semiconductor spintronic heterostructures as a model injector of spin-polarized carriers. (Eu,Gd)Te monocrystalline layers with Gd content up to 5 at. % were grown by MBE on BaF2 (111) substrates with either PbTe or EuTe buffer layers. Measurements of magnetic susceptibility and magnetization revealed that the ferromagnetic transition with the Curie temperature of Tc = 11-15 K is observed in (Eu,Gd)Te layers with n-type metallic conductivity. The analysis of the magnetization of (Eu,Gd)Te was carded out in a broad range of magnetic fields applied along various crystal directions, both in- and out of the layer plane. It revealed, in particular, that a rapid low-field ferromagnetic response of the (Eu,Gd)Te layer is followed by a paramagnetic-like further increase towards a full saturation. [ABSTRACT FROM AUTHOR]

The electron spin resonance, magnetization, and dynamic magnetic susceptibility of In1 – xMnxSe layered crystals (x = 0.0125) are studied. It is found that two different impurity subsystems independently coexist in the crystalline layer and in the interlayer spacing of unannealed samples. In both subsystems, ferromagnetic exchange interaction occurs between the Mn ions in the temperature range 300–140 K, and antiferromagnetic interaction occurs in the range 140–77 K. At temperatures below 77 K, a three-dimensional ferromagnetic order emerges. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

High and low field magnetotransport measurements, as well as SQUID measurements of magnetization, were carried out on Ga1− xMn xAs epilayers grown by low temperature molecular beam epitaxy, and subsequently annealed under various conditions. We observe a large enhancement of ferromagnetism when the samples are annealed at an optimal temperature, typically about 280°C. Such optimal annealing leads to an increase of Curie temperature, accompanied by an increase of both the conductivity and the saturation magnetization. A decrease of the coercive field and of magnetoresistivity is also observed for Ga1− xMn xAs annealed at optimal conditions. We suggest that the experimental results reported in this paper are related to changes in the domain structure of Ga1− xMn xAs. [ABSTRACT FROM AUTHOR]

We analyze critical temperature of ferromagnetic ordering in diluted magnetic semiconductors in the mean-field approximation. Using a general field-theoretical approach we formulate a description of magnetic phase transition, which takes into account the interaction of magnetic fluctuations. We also propose a mechanism of exchange interaction between Mn impurity moments in GaMnAs alloys via the Mn-induced acceptor levels. This mechanism may lead to low temperature ferromagnetism at vanishing concentration of free carriers. [ABSTRACT FROM AUTHOR]

Zero and longitudinal field μSR have been used to examine the singlet ground state magnetism of the diluted magnetic semiconductor Hg1-xFexSe. For x\geq 0.05\ μSR experiments indicate spin glass behaviour which is limited to sample regions with locally enhanced Fe2+ content. Longitudinal field spectra in the glassy state reveal a static local field \sim 50 mT due to induced moments of Fe2+. These are proposed to originate from a distribution of bound magnetic polaron energies. [ABSTRACT FROM AUTHOR]