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IV-VI semiconductors possess intriguing multifunctional characteristics, such as topological surface states, ferroelectricity at room temperature, and giant Rashba spin-splitting, giving them the potential for next-generation spintronic applications. In this work, we are presenting the epitaxially grown layers α-GeTe and SnTe, their structural and high field magnetotransport results. The crystal structure of α-GeTe preserves the rhombohedral symmetry (R3m) below T~720 K manifesting ferroelectric polarization, whereas SnTe holds the cubic symmetry (Fm-3m) above T~80 K. The results of the variable temperature in the range 4.3≤T≤300 K show a weakly dependent charge concentration, i.e., p(T)=0.1×1021 cm-3 for SnTe and p(T)=0.7×1021 cm-3 for α-GeTe layers. Likewise, the hole mobility μh(T) remains almost constant in the range 4.3≤T≤15 K and changes to a metallic-like behavior when T≥15 K. Furthermore, the high field magnetoresistance ρxx(B) graphs of SnTe layers, measured between -13≤B≤13 T, demonstrate a prominent weak anti-localization effect below T=3 K and when |B|≤0.3 T. However, the weak anti-localization effect disappears at T=4.2 K for both the α-GeTe and SnTe epitaxial layers. Similarly, the ρxx(B) graphs of α-GeTe show a small effect only at the lowest temperature measured T=1.6 K. The calculated prefactor value α=-14, obtained by fitting the Δσxx(B) graphs with the Hikami-Larkin-Nagaoka model, indicates the bulk transport system in SnTe. [ABSTRACT FROM AUTHOR]

• Ge 1- x - y Sn x Mn y Te epitaxial layers were grown via molecular beam epitaxy. • Longitudinal resistivity identifies electron–electron interaction. • Negative magnetoresistance is detected at low temperatures. • The layers manifest extrinsic anomalous Hall resistivity. • Both skew scattering and side jump contribute to anomalous Hall effect. In this work, we present the structural, magnetic and magnetotransport results of Ge 1− x − y Sn x Mn y Te thin layers with x = 0.076–0.22 and y = 0.051–0.16. The samples were grown via molecular beam epitaxy with thickness ranging from 160 nm to 900 nm. From X-ray diffraction analysis, the layers maintain low symmetry rhombohedral crystal structure inherited from the host lattice. The rhombohedral distortion is well-maintained in alloyed layers even in the sample with the highest Sn and Mn contents, x ≈ 0.22 and y ≈ 0.051. The dc magnetic susceptibility, χ dc (T) of all three layers manifests large bifurcation in the field-cooled/zero-field-cooled curves which might represent frustrated magnetic state interpreted as possible cluster-glass order. From high field magnetotransport results, a negative to positive crossover in magnetoresistance is observed for y = 0.11 at T ≈ 36 K. Furthermore, we also present a modified scaling results of anomalous Hall resistivity which displays a large magnitude, ρ AH ≈ 4.9 μΩcm at T = 4.2 K for the layer with y = 0.11. The scaling results show that both skew scattering and side-jump mechanisms contribute to the anomalous Hall effect in Ge 1− x − y Sn x Mn y Te samples however; the later seems to be dominant driving mechanism. [ABSTRACT FROM AUTHOR]

This study explores the use of Secondary Ion Mass Spectrometry (SIMS) to accurately measure the content of Pb 1 − x Sn x Te , a new class of electronic materials known as Topological Crystalline Insulators (TCIs). We analyzed the SIMS signal ratios of SnCs + / PbCs + and Sn ± / Pb ± in thin layers and determined the calibration curves necessary to estimate the exact amount of content in this ternary compound. Additionally, we investigated the matrix effect and performed depth profiling to obtain a more precise determination of the content. These findings contribute to the understanding and development of TCIs, and highlight the potential of SIMS for accurate content determination in ternary compounds. • Calibration curve for Secondary Ion Mass Spectrometry were developed for ternary compounds of Pb 1 − x Sn x Te. • The comparison of matrix effect between positive and negative secondary ions. • Cs cluster method gives the most proper results for determining the matrix composition. [ABSTRACT FROM AUTHOR]

The recent discovery of a topological phase transition in IV-VI narrow-gap semiconductors has revitalized the decades-old interest in the bulk band inversion occurring in these materials. Here we systematically study the (001) surface states of Pb⩽sub⩾1-x⩽/sub⩾Sn⩽sub⩾x⩽/sub⩾Se mixed crystals by means of angle-resolved photoelectron spectroscopy in the parameter space 0 ⩽ x ⩽ 0.37 and 300 K ⩾ T ⩾ 9 K. Using the surface-state observations, we monitor directly the topological phase transition in this solid solution and gain valuable information on the evolution of the underlying fundamental band gap of the system. In contrast to common model expectations, the band-gap evolution appears to be nonlinear as a function of the studied parameters, resulting in the measuring of a discontinuous band-inversion process. This finding signifies that the anticipated gapless bulk state is in fact not a stable configuration and that the topological phase transition therefore exhibits features akin to a first-order transition. [ABSTRACT FROM AUTHOR]

We present angle-resolved photoemission spectroscopy measurements of the surface states on in-situ grown (111) oriented films of Pb1-xSnxSe, a three-dimensional topological crystalline insulator. We observe surface states with Dirac-like dispersion at ̄Γ and ̄M in the surface Brillouin zone, supporting recent theoretical predictions for this family of materials. We study the parallel dispersion isotropy and Dirac-point binding energy of the surface states, and perform tight-binding calculations to support our findings. The relative simplicity of the growth technique is encouraging, and suggests a clear path for future investigations into the role of strain, vicinality, and alternative surface orientations in (Pb,Sn)Se solid solutions. [ABSTRACT FROM AUTHOR]

Topological insulators are a class of quantum materials in which time-reversal symmetry, relativistic effects and an inverted band structure result in the occurrence of electronic metallic states on the surfaces of insulating bulk crystals. These helical states exhibit a Dirac-like energy dispersion across the bulk bandgap, and they are topologically protected. Recent theoretical results have suggested the existence of topological crystalline insulators (TCIs), a class of topological insulators in which crystalline symmetry replaces the role of time-reversal symmetry in ensuring topological protection. In this study we show that the narrow-gap semiconductor Pb1?xSnxSe is a TCI for x? = ?0.23. Temperature-dependent angle-resolved photoelectron spectroscopy demonstrates that the material undergoes a temperature-driven topological phase transition from a trivial insulator to a TCI. These experimental findings add a new class to the family of topological insulators, and we anticipate that they will lead to a considerable body of further research as well as detailed studies of topological phase transitions. [ABSTRACT FROM AUTHOR]

Ferromagnetic and structural properties of semimagnetic (diluted magnetic) monocrystalline Ge1-xMnxTe layers (x = 0.04 and x = 0.19) grown by molecular beam epitaxy on BaF2(III) substrates were experimentally studied by the SQUID magnetometry and by high resolution X-ray diffraction analysis. Based on the temperature dependence of the lattice parameter, the structural phase transition from the rock salt to the rhombohedral crystal lattice was experimentally found at T = 675 K in Ge1-xMnxTe (x = 0.04) layer. The ferromagnetic Curie temperature Tc in Ge1-xMnxTe layers was determined based on the measurements of temperature and magnetic field dependence of magnetization. In Ge1-xMnxTe with the highest Mn content studied (x = 0.19) the mean-field like analysis of magnetic properties showed the Curie temperature Tc = 40 K. [ABSTRACT FROM AUTHOR]

(Eu,Gd)Te ferromagnetic semiconductor layers grown by molecular beam epitaxy technique on BaF2 (111) monocrystalline substrates were investigated by resonant photoemission spectroscopy using synchrotron radiation. In n-(Eu,Gd)Te layers, a ferromagnetic transition induced by electron concentration is observed. Magnetic as well as electrical properties of this material depend strongly on the charge state (2+ vs. 3+) of Eu and Gd ions known to be sensitive to crystal stoichiometry and formation of oxide complexes. The relative concentration of Eu2+ and Eu3+ ions was determined from the analysis of the resonant photoemission energy distribution curves (EDC), measured at photon energies close to 4d-4f resonance. After various in-situ annealing and Ar sputtering procedures, a clear improvement of crystal stoichiometry of (Eu,Gd)Te layers was observed as manifested by the increase of Eu2+ intensity in the spectra. Contribution of Eu 4f shell to the total density of states was also analyzed and found at the valence band edge for Eu2+ ions and about 6 eV lower for Eu3+ ions. [ABSTRACT FROM AUTHOR]

Magnetic properties of thin layers of p-Ge1-xMnxTe (x< 0.2) semimagnetic (diluted magnetic) semiconductor exhibiting carrier induced ferromagnetism were experimentally studied. The layers were grown on BaF2 (111) substrates by molecular beam epitaxy technique. X-ray diffraction analysis performed at room temperature revealed monocrystalline (111)-oriented :rhombohedral (exhibiting ferroelectric properties) crystal structure of Ge1-xMnxTe layers in the entire range of Mn content studied. The examination of the magnetic properties of the layers carried out by superconducting SQUID magnetometry and ferromagnetic resonance technique showed the ferromagnetic transition with the Curie temperature in the range 10-100 K depending on the Mn content and the hole concentration. Contrary to polycrystalline GeMnTe layers, it was experimentally found that in monocrystalline layers of GeMnTe an easy magnetization axis is directed along a normal to the layer plane. This effect is discussed in terms of strain present in these layers due to thermal expansion coefficients mismatch between the substrate and the GeMnTe layer. [ABSTRACT FROM AUTHOR]

Abstract: Ferromagnetic n-(Eu,Gd)Te/p-PbTe semiconductor heterostructures were grown by molecular beam epitaxy on BaF2 (111) monocrystalline substrates. The epitaxial growth of the layers was controlled in situ by reflection high-energy electron diffraction. X-ray diffraction and atomic force microscopy techniques revealed high structural and morphological quality of deposited layers. Gd content up to 5at.% in (Eu,Gd)Te layers was estimated by energy dispersive X-ray fluorescence analysis. Hall effect measurements in (Eu,Gd)Te layers showed very high electron concentration of n ≈1020 cm−3 present due to Gd doping. Magnetic characterization of (Eu,Gd)Te/PbTe heterostructures was done using SQUID magnetometry and revealed ferromagnetic transition in n-(Eu,Gd)Te with the Curie temperature T C =11–15K. Both in-plane resistance of (Eu,Gd)Te layer and (normal to the plane) (Eu,Gd)Te–PbTe junction resistance measurements were carried out as a function of temperature and magnetic field showing changes in charge transport processes at temperatures close to the Curie temperature. [Copyright &y& Elsevier]

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]

Abstract: Resonant photoemission study of electronic structure of molecular beam epitaxy grown Eu1−x Gd x Te layers without and with cover protected layer of Te were performed using synchrotron radiation. The analysis of the valence band and shallow core levels spectra of the clean surface of Eu1−x Gd x Te obtained in situ under UHV conditions showed the existence of Eu2+ and Eu3+ ions in the layers. The trivalent europium ions mostly are located at the surface and its amount strongly depends on sample surface preparation conditions. The prolonged annealing of Eu1−x Gd x Te layers covered with protected layer of Te leads to formation of clean surface of the sample not changing the stoichiometry of it and without the accumulation of Eu3+ ions at the surface region. [Copyright &y& Elsevier]

The paper presents photoemission study of core level binding energy shifts caused by local crystalline structure collapse in cubic Pb 1− x Cd x Te crystal. Photoemission spectra of two kinds of semiconductor samples are compared. The first one is ternary crystal of Pb 0.94 Cd 0.06 Te with the frozen rock salt structure where the crystalline local structure collapse is expected due to the difference of ion radii of Cd and Pb cations. The second sample was the CdTe(22 nm)/PbTe(6 nm)/CdTe(4 μm)/GaAs(1 1 1)B nanostructure grown by molecular beam epitaxy (MBE) method, where crystalline local structure is not expected to be created. The photoemission spectra show that for the crystal with local structure the electron binding energies of cations are higher (e.g. +0.2 eV) whereas for anions they are lower (e.g. −0.08 eV) than in the multilayer structure. A model is proposed to explain obtained results by the local crystalline structure collapse in Pb 0.94 Cd 0.06 Te crystal. [ABSTRACT FROM AUTHOR]

In this paper the physical properties of two types of Co-doped ZnO nanostructures: tetrapods and nanofibers grown by a rapid thermal evaporation process and prepared by the electrospinning technique, respectively, were investigated and analyzed. Surface morphology of the samples was examined using scanning electron microscopy. X-ray diffraction measurements showed hexagonal wurtzite crystal structure of both types of investigated nanostructures. Both X-ray diffraction and Raman scattering data confirmed high phase purity of the samples. The magnetic properties studied with the use of the SQUID magnetometer confirmed a presence of ferromagnetic order in analyzed nanostructures. The observed photoluminescence spectra exhibited two groups of lines. The first one, in the ultraviolet spectral range, is due to the optical transitions close to ZnO band gap, the second one in the red region is most probably related to the Co2+ d-d internal transitions. The influence of native defects on the optical properties is also shown and discussed. All results reported here lead us to the conclusion that in the mixed crystal nanostructures obtained, a fraction of the Zn2+ ions is substituted by Co2+ ions. [ABSTRACT FROM AUTHOR]

We demonstrate an efficient energy conversion in a p-n thermoelectric couple built of bulk Pb0.95Mn0.05Te crystals grown by the Bridgman method and heavily doped n-type with Bi (n = 1:9 × 1019cm-3) or p-type with Na (p = 2:3 × 1019cm-3). Substitution of Mn2+ ions for Pb2+ ions at the rock-salt lattice cation sites increases the band gap of Pb1-xMnxTe and decreases the energy separation between the light hole Σ-band and the heavy hole R-band. It results in a large increase of thermoelectric power and improved thermoelectric parameters of p-type Pb1-xMnxTe. Applying the Harman method for samples of various lengths, we experimentally determined the radiation correction factors and found the thermoelectric figure of merit parameter ZT = 0:75-0:8 at T = 650 K for both n- and p-type materials with good thermoelectric matching of the couple. We report on thermoelectric performance of a p-n thermoelectric couple assembled of these materials and tested over the T = 300-670 K temperature region. [ABSTRACT FROM AUTHOR]

Abstract: Silicon single crystals were implanted with 160keV Mn+ ions to a dose of 1×1016 cm−2 and next annealed for 1h up to 1070K under ambient pressure. Glancing incidence diffraction research performed using synchrotron radiation indicated that the post-implantation treatment influenced the creation of Mn4Si7 nanoinclusions. The dimensions and concentration of these inclusions, calculated from distribution of the X-ray diffuse scattering intensity are dependent on annealing temperature. The sizes and shapes of the inclusions were also determined by high-resolution transmission electron microscopy. Magnetic properties of the Si:Mn samples were studied using superconducting quantum interference device. The origin of ferromagnetic ordering is discussed in terms of the size of nanoinclusions. [Copyright &y& Elsevier]

Temperature and magnetic field dependence of magnetization of EuS-SrS multilayers grown epitaxially on KCl (001) substrate is experimentally studied by superconducting magnetometry technique. In these lattice-matched semiconductor heterostructures EuS layers are ferromagnetic quantum wells whereas SrS layers are nonmagnetic spacer barriers. The multilayers composed of EuS layers with thickness 3.5-5 nm and SrS layers (thickness 0.5- 10 nm) exhibit ferromagnetic transition at 17 K. In the multilayers with ultrathin SrS spacers (0.5-1 nm) a nonmonotonic temperature dependence of magnetization as well as a characteristic switching in magnetic hysteresis loops is observed. These experimental findings are explained considering antiferromagnetic interlayer coupling between ferromagnetic EuS layers via nonmagnetic SrS spacers. The strength of this coupling is determined based on model magnetization calculations. [ABSTRACT FROM AUTHOR]

We study the nature of (001) surface states in Pb0.73Sn0.27Se in the newly discovered topological-crystalline-insulator (TCI) phase as well as the corresponding topologically trivial state above the band-gap-inversion temperature. Our calculations predict not only metallic surface states with a nontrivial chiral spin structure for the TCI case, but also nonmetallic (gapped) surface states with nonzero spin polarization when the system is a normal insulator. For both phases, angle- and spin-resolved photoelectron spectroscopy measurements provide conclusive evidence for the formation of these (001) surface states in Pb0.73Sn0.27Se, as well as for their chiral spin structure. [ABSTRACT FROM AUTHOR]

The dynamic and static magnetic properties of La1.85Sr0.15Cu1-yNiyO4 with Ni concentration up to y=0.63 are reported. All the features that characterize the spin-glass (SG) behavior are found: bifurcation of the dc susceptibility ᵡ versus temperature curve, a peak in the zero-field-cooling branch of this curve accompanied by a step in the imaginary part of the ac susceptibility ᵡac, frequency dependence of the peak position in the real part of ᵡ ac, and scaling behavior. The decay of remanent magnetization is described by a stretched-exponential function. The characteristic time from the critical slowing-down formula that governs the dynamics of the system suggests the existence of the spin clusters. The strongest interactions between the fluctuating entities are at y equal to the charge-carrier concentration in the system. The SG transition temperature decreases linearly with decreasing y for y ⩽ 0.30 and extrapolates to 0 K at y=0, which means that Ni displays a magnetic character in the surrounding Cu-O network starting from the smallest concentration y. The static critical exponents characterizing the scaling behavior of the nonlinear part of ᵡ lie between those typical for three-dimensional Ising-like and Heisenberg-like systems. [ABSTRACT FROM AUTHOR]

Abstract: MBE growth conditions, SEM and XRD structural characterization and experimental studies of optical properties are presented for Pb1−x Eu x Te/CdTe semiconductor heterostructures grown on GaAs (001) substrate with a thick CdTe buffer layer. Photoluminescence excited by pulsed YAG:Nd laser was studied in the mid-infrared spectral region for 12.5nm-thick Pb1−x Eu x Te quantum wells (x=0–0.038) with 75nm-thick CdTe barriers. Increasing the Eu content up to about 4at% permitted large infrared photoluminescence tuning from 0.34 to 0.465eV due to the increase in Pb1−x Eu x Te bandgap. [Copyright &y& Elsevier]

Abstract: PbTe (001) nanowires have been synthesized by thermal evaporation in a high vacuum using vapor–liquid–solid growth mechanism with Bi catalyst on KCl (001) substrate. Transmission and scanning electron microscopy as well as X-ray diffraction technique were employed in order to inspect nanowire structure. Having rock salt (NaCl) structure, the nanowires uniform in diameter grew along [001] axis and were perpendicular to the substrate plane. The cross-section of PbTe nanowires was found to be rectangular in shape and nanowire walls turned out to be faceted by {100} plains that are the most energetically favorable type of planes for NaCl type of structure. Mean nanowire diameter was found to be 50–200nm depending on size of Bi catalyst droplets. The half-width of (002) maximum on X-ray rocking curve was found of the order of 0.3–0.5°, no worse than typical value obtained for KCl substrate. No tapering and other defects like twins were observed. [Copyright &y& Elsevier]

The influence of Ni doping on the normal-state pseudogap in La1.85Sr0.15CuO4 is studied by dc magnetic susceptibility measurements, accompanied by X-ray powder diffraction analysis and resistivity measurements. The measurements are carried out on the polycrystalline La1.85Sr0.15Cu1-yNiyO4 samples in the whole doping range from y = 0.01 up to y = 1. The temperature of pseudogap opening is found to decrease above y = 0.05 and to vanish when y exceeds 0.07. At small Ni content, up to y = 0.07, the magnetic moment induced by Ni is constant and equal to 0.7 μB per Ni, while for larger y it increases abruptly and reaches about 1.6 μB per Ni ion for y = 0.5. The dependence of the normal-state resistivity on temperature evolves smoothly from the metallic-like for small y, to the variable range hopping, described by the Mott law with the exponent 1/4, for samples with y > 0.15. [ABSTRACT FROM AUTHOR]

The magnetic properties of La1:85Sr0:15CuO4 doped with Ni was investigated in the field up to 5 T and in the temperature range from 2 K to 400 K using both dc and ac techniques. For Ni content larger than 0.05 the system exhibits irreversibility of low-field susceptibility x(T) below a certain temperature depending on y and a cusp at Tg in x(T) measured after zero-field cooling. The decay of remnant magnetization below Tg with time is described by a stretched-exponential function. In accordance with scaling theory, all the x(T) data for y = 0:50 sample taken in the vicinity of Tg at different fields collapse onto two separate curves when plotted as q∣t∣-β vs. B2∣t-∣-β-γ, where q is the spin-glass order parameter, t = (T - Tg)=Tg, and β and γ are the critical exponents. All these features taken together reveal existence of spin-glass phase below Tg. Variation of Tg with y is linear below y = 0.25 and Tg extrapolates to 0 K for y → 0 what strongly suggests that spin-glass phase extends into superconducting region of the phase diagram. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we used far-infrared spectroscopy, reflection high energy electron diffraction (RHEED), X-ray diffraction and atomic force microscopy (AFM) to investigate structural and optical properties of Pb1−x Mn x Te layers grown by molecular beam epitaxy (MBE). A numerical model for calculating the reflectivity coefficient for complex systems which include films, buffer layer and substrate has been applied. The infrared reflectivity spectra consist of Pb1−x Mn x Te phonons, which exhibit intermediate one–two mode behavior, and MnTe phonons. A good agreement between calculated and experimental spectra is achieved. We registered the local distribution of Mn impurities depending on substrate type. For films growth on BaF2 substrate we registered the orthorhombic local structure of MnTe clusters, while in the case of KCl substrate this structure is cubic. The Pb1−x Mn x Te long wavelength optical phonons were described by the modified Genzel''s model. [Copyright &y& Elsevier]

Abstract: The electronic structure of Ge0.4 Mn0.5 Eu0.1 Te has been investigated by means of resonant photoemission spectroscopy. The spectra were acquired for the photon energy ranges of 130–155 and 40–60 eV corresponding to the Eu 4d   4f and Mn 3p   3d resonances, respectively. The features related to Eu 4f and Mn 3d states were revealed in the emission from the valence band. It was shown that europium ions occur as Eu2+. The Mn2+ 3d states contribute to the whole valence band with a maximum of the Mn 3d distribution at 3.9 eV. [Copyright &y& Elsevier]

Abstract: Substitution of Gd3+ for Eu2+ ions in EuTe leads to the introduction of Gd 5d electrons to the conduction band and antiferromagnetic order of EuTe (Heisenberg magnetic semiconductor) can be replaced by ferromagnetic state due to RKKY interaction. The layers were grown by MBE method on BaF2 (111) substrate. Layer of Te deposited on top of (EuGd)Te protects surface of oxidation. Heating in 320°C leads to Te atoms desorption and to improvement of the layer electronic structure. Additional Gd atoms were sequentially deposited on the layer of (PbGd)Te and set of Fano resonance curves were observed for ions of Gd. The Fano type photoemission resonance corresponding to the 4d–4f transitions were studied for Eu and Gd. [Copyright &y& Elsevier]

Abstract: The substitution of Gd3+ for Eu2+ ions introduces conducting electrons and qualitatively changes the model of description of magnetic properties of these semiconductor alloys: antiferromagnetic order observed in insulating layers of EuTe is replaced by ferromagnetic (RKKY interaction driven) state in metallic n-type (Eu,Gd)Te. The high-energy photoemission spectroscopy (hν =3000eV) was used to study the electronic structure and valence of magnetic ions in about one micron thick monocrystalline, ferromagnetic n-type (Eu,Gd)Te layers grown by molecular beam epitaxy on BaF2 (111) substrate with EuTe buffer layer. The photoemission spectra of Eu (3d,4d,4f), Gd (3d,4d,4f), Te (3d,4d) electrons as well as valence band electrons were measured after sequential Ar ion etching. For surface of the sample exposed to the air the oxidation of surface takes place and measured spectra showed the dominant Eu3+ contribution in comparison to Eu2+. The chemical shift of Te3d and Te4d peaks was observed for Te atoms oxidized on the surface. Surface sputtering by Ar ions removes the top layer with oxygen adsorbed at the surface and oxygen diffused in the surface region and clean (Eu,Gd)Te surface of the layer was measured. For clean surface the Eu2+ dominate in the spectra and the peaks of oxidized Te atoms disappear. The contribution of Eu2+ 4f electrons to the electronic structure of the (Eu,Gd)Te was found at the top of the valence band. [Copyright &y& Elsevier]

Bulk monocrystals of Pb1-xCdxTe, with the Cd content x up to 0.11, were grown by physical vapour transport method. The structural, electrical and optical properties of these ternary crystals were studied experimentally and theoretically. All investigated samples exhibit rock-salt structure and high crystal quality, which was confirmed by X-ray rocking curve width parameter of about 100 arcsec. The decrease of the lattice parameter with increasing Cd content x was found experimentally, in agreement with ab initio calculations. The band structures of Pb1-xCdxTe mixed crystals for x values up to 0.2 were calculated using tight binding approach. The calculated band gap in the L-point increases with the Cd content in qualitative agreement with photoluminescence measurements in the infrared. For all studied Pb1-xCdxTe samples, the Hall effect and electrical conductivity measurements, performed in the temperature range from 4 to 300 K, revealed p-type conductivity. [ABSTRACT FROM AUTHOR]

Ferromagnetic transition temperature in thin layers of diluted magnetic (semimagnetic) semiconductor Ge1-xMnxTe was studied experimentally by SQUID magnetometry method and analyzed theoretically for a model Ising-type diluted magnetic system with Ruderman-Kittel-Kasuya-Yosida indirect exchange interaction. The key features of the experimentally observed dependence of the Curie temperature on Mn content (x ⩽ 0.12) and conducting hole concentration p = (1-10)×1021 cm-3 were reproduced theoretically for realistic valence band and crystal lattice parameters of p-Ge1-xMnxTe taking into account short carrier mean free path encountered in this material and Ruderman-Kittel-Kasuya-Yosida mechanism with both delta-like and diffused character of spatial dependence of the exchange coupling between magnetic ions and free carriers. [ABSTRACT FROM AUTHOR]

In this work we studied domain structure of Zn1-xCoxO nanowires which are single arms of tetrapode crystals. The as-grown material exhibits hysteretic behavior even at room temperature as revealed by SQUID mesurements. In order to get insight into the magnetic properties of individual tetrapodes they were dismembered into nanowires of nanometric diameters, deposited on a flat substrate and imaged by magnetic force microscopy. A magnetic interaction between the magnetic force microscopy probe and single nanowires has been detected which confirms that nanometric volume of the material possesses a magnetic moment. The magnetic force microscopy contrast is attractively independent of the tip magnetization direction which indicates that shape anisotropy of nanowires is not strong enough to prevent occurrence of tip-induced magnetic field disturbance. [ABSTRACT FROM AUTHOR]

Abstract: Interlayer coupling was experimentally studied in semiconductor EuS–PbS ferromagnetic superlattice wedge structures grown on KCl (001) substrates with the wedges covering the semiconductor nonmagnetic PbS spacer layer thickness from 0.3 to 6nm. Structural parameters of the wedges were examined by X-ray diffraction analysis of EuS–PbS superlattice period. Measurements of magnetic hysteresis loops of EuS–PbS structures were performed by both SQUID (for small terminal parts of the wedge) and MOKE (magneto-optical analysis along the wedge) magnetometry. A strong decrease of magnetic remanence and an increase of saturation field observed for EuS–PbS structures with the PbS spacer thickness decreasing below about 1.5nm is discussed in terms of the influence of antiferromagnetic interlayer coupling. [Copyright &y& Elsevier]

Magnetization, anomalous Hall effect, thermoelectric power, magnetoresistance, and resistivity of Sn1-x-y-zGexMnyGdzTe (x = 0:039 ÷ 0:597, y = 0:077 ÷ 0:125, z = 0:0014 ÷ 0:028) mixed crystals were studied over the temperature range 4.2-300 K. The ferromagnetic order with Curie temperature 18-24 K was revealed. [ABSTRACT FROM AUTHOR]

Since the advent of topological insulators hosting Dirac surface states, efforts have been made to gap these states in a controllable way. A new route to accomplish this was opened up by the discovery of topological crystalline insulators where the topological states are protected by crystal symmetries and thus prone to gap formation by structural changes of the lattice. Here we show a temperature-driven gap opening in Dirac surface states within the topological crystalline insulator phase in (Pb,Sn)Se. By using angle-resolved photoelectron spectroscopy, the gap formation and mass acquisition is studied as a function of composition and temperature. The resulting observations lead to the addition of a temperature- and composition-dependent boundary between massless and massive Dirac states in the topological phase diagram for (Pb,Sn)Se (001). Overall, our results experimentally establish the possibility to tune between massless and massive topological states on the surface of a topological system. [ABSTRACT FROM AUTHOR]

Abstract: The electronic structure of polycrystalline Ge0.86Mn0.14Te—ferromagnetic semiconductor with T C=110K, has been studied by means of resonant photoemission spectroscopy for photon energies close to the Mn 3p→3d excitation. The contribution of Mn 3d states to the electronic structure of the system was revealed and position of the Mn ions in the crystal, characteristic of GeTe-based diluted magnetic semiconductors was proved. [Copyright &y& Elsevier]