Native vacancy defects in Zn1-x(Mn,Co)xGeAs2 studied with positron annihilation spectroscopy

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.Peer reviewe

Growth conditions, structure, and superconductivity of pure and metal-doped FeTe1-xSex single crystals

Superconducting single crystals of pure FeTe1 xSex and FeTe0.65Se0.35 doped with Co, Ni, Cu, Mn, Zn, Mo, Cd, In, Pb, Hg, V, Ga, Mg, Al, Ti, Cr, Sr or Nd into Fe ions site have been grown applying Bridgman's method. It has been found that the sharpness of transition to the superconducting state in FeTe1 xSex is evidently inversely correlated with crystallographic quality of the crystals. Among all of the studied dopants only Co, Ni and Cu substitute Fe ions in FeTe0.65Se0.35 crystals. The remaining examined ions do not incorporate into the crystal structure. Nevertheless, they form inclusions together with selenium, tellurium and/or iron, what changes the chemical composition of host matrix and therefore influences Tc value. Small disorder introduced into magnetic sublattice, by partial replacement of Fe ions by slight amount of nonmagnetic ions of Cu (~ 1.5 at%) or by magnetic ions of Ni (~ 2 at%) and Co (~5 at%) with spin value different than that of Fe ion, completely suppresses superconductivity in FeTe1 xSex system. This indicates that even if superconductivity is observed in the system containing magnetic ions it can not survive when the disorder in magnetic ions sublattice is introduced, most likely because of magnetic scattering of Cooper pairs.Comment: 18 pages, 12 figures, 3 table

Good electrical contacts for high resistivity (Cd,Mn)Te crystals

We consider that semi-insulating (Cd,Mn)Te crystals may well successfully replace the commonly used (Cd,Zn)Te crystals as a material for manufacturing large-area X- and gamma-ray detectors. The Bridgman growth method yields good quality and high-resistivity (10{sup 9}-10{sup 10} {Omega}-cm) crystals of (Cd,Mn)Te:V. Doping with vanadium ({approx} 10{sup 16} cm{sup -3}), which acts as a compensating agent, and annealing in cadmium vapors, which reduces the number of cadmium vacancies in the as-grown crystal, ensure this high resistivity. Detector applications of the crystals require satisfactory electrical contacts. Hence, we explored techniques of ensuring good electrical contacts to semi-insulating (Cd,Mn)Te crystals. Our findings are reported here. Before depositing the contact layers, we prepared an 'epi-ready' surface of the crystal platelet by a procedure described earlier for various tellurium-based II-VI compound crystals. A molecular beam epitaxy (MBE) apparatus was used to deposit various types of contact layers: Monocrystalline semiconductor layers, amorphous- and nanocrystalline semiconductor layers, and metal layers were studied. We employed ZnTe heavily doped ({approx} 10{sup 18} cm{sup -3}) with Sb, and CdTe heavily doped ({approx} 10{sup 17} cm{sup -3}) with In as the semiconductors to create contact layers that subsequently enable good contact (with a narrow, tunneling barrier) to the Au layer that usually is applied as the top contact layer. We describe and discuss the technology and some properties of the electrical contacts to semi-insulating (Cd,Mn)Te

Crystalline Structure of Potassium Holmium Double Tungstate

The potassium holmium double tungstate was prepared by using top seeded solution growth technique. Structural investigations have been performed at room temperature. The KHo(WO4)2 single crystal belongs to the monoclinic space group C2/c with the unit-cell parameters: a = 10.624(2) Å, b = 10.352(2) Å, c = 7.5434(15) Å, β = 130.7

The magnetic properties of potassium holmium double tungstate

The magnetic investigations of potassium holmium double tungstate KHo(WO⁴)² have been performed. The results of measurements of magnetic susceptibility and magnetization as a function of temperature (T from 0.3 K up to 100 K) and magnetic field (up to 1.5 T) are presented. A strong anisotropy of magnetic properties was found. The magnetic measurements data were used to calculate the interaction energy. It was shown that the interactions between nearest neighbors Ho³⁺ ions have antiferromagnetic character

AC Magnetic Susceptibility Studies of Ge1−x−ySnxMnyTeGe_{1-x-y}Sn_{x}Mn_{y}Te Mixed Crystals

We present preliminary studies of magnetic and transport properties of $Ge_{1-x-y}Sn_xMn_yTe$ mixed crystals with 0.091 ≤ x ≤ 0.105 and 0.012 ≤ y ≤ 0.115. Qualitative analysis of our experimental results showed the appearance of a spin-glass phase at T $10^{21} cm^{-3}$) and low mobilities (μ < 100 $cm^2 V^{-1} s^{-1}$). The dependence of transport properties on the chemical composition of the samples was observed

Preparation and Optical Properties of Zn1−x\text{}_{1-x}Mnx\text{}_{x}Te1−y\text{}_{1-y}Oy\text{}_{y} Highly Mismatched Alloy

The Zn$\text{}_{1-x}$Mn$\text{}_{x}$Te$\text{}_{1-y}$O$\text{}_{y}$ alloy was prepared using a rapid crystallization technique. X-ray diffraction measurements were used to estimate the oxygen doping level. It is demonstrated that the oxygen solubility in Zn$\text{}_{1-x}$ Mn$\text{}_{x}$Te$\text{}_{1-y}$O$\text{}_{y}$ alloys greatly depends on the manganese concentration. No oxygen related effects were observed in the manganese free samples. The highest value of the oxygen molar fraction (y) achieved in the present study was 0.0023 in a sample having manganese fraction (x) of 0.056. The decrease in the alloy band gap was observed with increasing oxygen content. The oxygen-related trap level in Zn$\text{}_{1-x}$Mn$\text{}_{x}$Te$\text{}_{1-y}$O$\text{}_{y}$ was found to be strongly shifted with respect to that in ZnTe$\text{}_{1-y}$O$\text{}_{y}$. The shift is assigned to a creation of complex (Mn$\text{}_{x}$O) traps

Effect of the In-Plane Epitaxial Mismatch between the Substrate and the Film on the Properties of YBa2\text{}_{2}Cu3\text{}_{3}O7−δ\text{}_{7-δ} Films

We study the effect of the in-plane epitaxial mismatch between the substrate and the film on the crystallographic structure and the transport properties of YBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{7-δ}$ superconducting films of thicknesses ranging between 600 and 3000Å. The films are grown by pulsed laser deposition on the new type of single-crystalline substrates prepared by Czochralski method, with the chemical formula (SrAl$\text{}_{0.5}$Ta$\text{}_{0.5}$O$\text{}_{3}$)$\text{}_{0.7}$(CaAl$\text{}_{0.5}$Ta$\text{}_{0.5}$O$\text{}_{3}$)$\text{}_{0 .1}$(LaAlO$\text{}_{3}$)$\text{}_{0.2}$. We find that superconducting properties of the samples are excellent, and generally they improve with increasing of the film thickness as a result of improved structural ordering. We also investigate the influence of the film thickness on the behavior of the critical current densities