Transport Properties Of Single Crystals Research Articles

Weak ferromagnetism in single crystalline YbB6−δ

We present a study of magnetization and transport properties of single crystals of YbB6 and YbB6±δ (δ=0.3 as a nominal value). The YbB6−δ crystal revealed a weak ferromagnetism, manifested by hysteresis loop in M(H) at room temperature with a saturation magnetic moment of 1.5×10−4μB∕f.u. and the ferromagnetic transition temperature higher than T=300K, whereas YbB6 and YbB6+δ crystals revealed diamagnetism and paramagnetism, respectively. It was found that the bulk magnetic property of YbB6±δ crystals is intrinsically diamagnetic and that the magnetism, ferromagnetism, or paramagnetism is a surface effect. Based on x-ray photoelectron spectroscopy and electron probe microanalyzer measurements, we believed that the extraneous magnetic impurities, such as Fe and Ni, are not the origin of the ferromagnetism or paramagnetism. While we observed from electrical resistivity and Hall resistivity that the off stoichiometry in YbB6±δ causes carrier doping effect, it is not clear at present what surface state creates the magnetic signals.

Multiphase magnetic state of Ca1 − x La x MnO3 − δ single crystals (x = 0.03, 0.05, 0.07) containing oxygen vacancies

Magnetic properties (magnetization, dynamic and static susceptibility) and transport properties (resistance and magnetoresistance) have been studied in a temperature range of 2–600 K in magnetic fields to 90 kOe for single crystals of Ca1 − xLaxMnO3 − δ with a weak electron doping (x ≤ 0.07) grown in argon and oxygen atmospheres. The magnetic state of Ca1 − xLaxMnO3 − δ single crystals is multiphase. Below T = TN(G) ∼ 110 K, in all the crystals there coexists an AFM G phase with an FM contribution and an AFM C phase. In crystals with x = 0.07, a transition from the paramagnetic phase into the AFM C phase occurs in part of their volume below T ∼ 130–150 K. In crystals with x = 0.05 annealed in oxygen, an anomaly of paramagnetic susceptibility is observed near T* ∼ 270 K, which is related to the formation of FM clusters near defects. At x = 0.05 and 0.07, AFM correlations are retained in the paramagnetic state (to 600 K). The differences in the magnetic and transport properties of single crystals grown in argon and oxygen are explained by the various content of oxygen vacancies and by their possible ordering.

Stabilization of antiferromagnetic phases by magnetic field annealing in phase separated manganites Pr 1− xCa xMnO 3

We report a detailed study on the effects of magnetic field annealing on the magnetic and transport properties of single crystals of Pr 1− x Ca x MnO 3 with x = 0.2 – 0.4 . Below the Néel temperature, the samples with 0.3 ≤ x ≤ 0.35 undergo a typical metamagnetic transition from antiferromagnetic (AFM) to ferromagnetic (FM) upon applying a field of about 3 T. After the first metamagnetic transition, remarkably, the critical field of the second metamagnetic transition is increased by about 1 T, suggesting that the AFM phase is stabilized by the magnetic field-annealing. This field-stabilized AFM phase might be attributed to the coexistence of inhomogeneous FM and AFM phases near the phase boundary that are strongly dependent upon a magnetic field. A general phase diagram of Pr 1− x Ca x MnO 3 is thus modified on the basis of irreversible magnetic transitions.

Magnetic and transport properties of [formula omitted] and [formula omitted

We report on magnetic and transport properties of single crystals of the light rare earth containing series of compounds RCoIn 5 ( R = Pr , Nd ) and heavy rare earth containing series RCoGa 5 ( R = Tb – Tm ). All the compounds crystallize in the tetragonal HoCoGa 5 crystal structure and are very good metals with small defect scattering at low temperatures. NdCoIn 5 and members of the RCoGa 5 series with large de Gennes factors order antiferromagnetically.

Polaron hopping properties of [formula omitted] ( [formula omitted

Using temperature- and field-dependent resistivity ρ ( T , H ) and Hall coefficient R H ( T , H ) measurements, we investigate the anomalous transport properties of single crystals of Eu 1 - x Ca x B 6 ( x = 0.2 – 0.995 ). The replacement of Eu with Ca invokes drastic changes in the ρ ( T ) and R H ( T , H ) although Eu and Ca are isoelectric. It is found that the Hall mobility, defined as | μ H | = R H ( H = 1 T ) / ρ , can be expressed by a non-adiabatic small polaron hopping model with four-neighbor hopping sites for Eu 1 - x Ca x B 6 ( x = 0.2 ) and with three-neighbor hopping sites for Eu 1 - x Ca x B 6 ( x = 0.9 ). The Hall mobility of Eu 1 - x Ca x B 6 ( x = 0.6 ) is expressed well by either the four- or three-sites hopping model. On the other hand, the DC conductivity of Eu 1 - x Ca x B 6 ( x ⩾ 0.95 ) is found to be described well by an adiabatic small polaron hopping model. Furthermore, the DC conductivity of Eu 1 - x Ca x B 6 ( x = 0.9 ) can also be described well by the adiabatic polaron hopping process. From the above observations, we surmise that the electronic transport properties of Eu 1 - x Ca x B 6 are dominated by the small polaron hopping mechanism. The hopping mechanism changes gradually from adiabatic for x ⩾ 0.9 to three-sites non-adiabatic for 0.9 ⩾ x ⩾ 0.6 and to four-sites non-adiabatic for x ⩽ 0.6 .

Drastic annealing effects in transport properties of single crystals of theYbNi2B2Cheavy fermion system

We report temperature dependent resistivity, specific heat, magnetic susceptibility and thermoelectric power measurements made on the heavy fermion system YbNi2B2C, for both as grown and annealed single crystals. Our results demonstrate a significant variation in the temperature dependent electrical resistivity and thermoelectric power between as grown crystals and crystals that have undergone optimal (150 hour, 950 C) annealing, whereas the thermodynamic properties: (c_p(T) and chi(T)) remain almost unchanged. We interpret these results in terms of redistributions of local Kondo temperatures associated with ligandal disorder for a small (~ 1%) fraction of the Yb sites.

Anisotropic properties of rare-earth dibismites

We report measurements of magnetic, thermal and transport properties of single crystals of rare-earth dibismites RBi 2 (R=La–Nd, Sm), grown via self-flux method. All compounds are good metals, and those with magnetic ions order antiferromagnetically at low temperatures. Ce, Pr and Sm members of the series show single magnetic transition whereas NdBi 2 most likely exhibits two magnetic transitions. Significant magnetic anisotropy and a series of metamagnetic transitions in fields up to 55 kG are found in PrBi 2. Ordering temperatures range from 3 K to just above 16 K and they scale well with the de Gennes factor.

Application of the photoacoustic method for characterization of natural galena (PbS)

Electron transport properties of single crystal and polycrystalline natural mineral galena (PbS) samples from the Trepca mine, Yugoslavia, were determined using the photoacoustic frequency transmission technique. Their thermal diffusivity (DT≈0.16 × 10−5 m2 s−1), the coefficient of diffusion (D between 0.15×10−2 0.16×10−2 m2 s−1) and lifetime of the excess carrier (τ≈35 μs and the front and rear recombination velocity (sg≈65.5 m s−1 and sb≈66.4 m s−1, respectively), were calculated by comparing the experimental results and the theoretical photoacoustic amplitude and phase signals. The lattice parameter obtained by X-ray work was a =5.936 A. The free carrier concentration of these single-crystal samples was measured using the Hall method (N = 3×1018 cm−3). Measurements of the optical reflectivity of the same samples, as a function of wavelength, in the infrared and far infrared ranges, were performed. In the far infrared range a free electron plasma frequency was observed and numerically analyzed, using the least-squares fitting procedure. The values of optical parameters were calculated and the value of the free carrier concentration obtained by the Hall method was confirmed.

C-axis transport in the intrinsically layered superconductor κ-(BEDT-TTF) 2Cu(NCS) 2: interplay between Josephson and quasiparticle tunneling

We have measured the transverse electrical transport properties of single crystals of the intrinsically layered organic superconductor κ-(BEDT-TTF) 2Cu(NCS) 2 in magnetic fields applied perpendicular to the superconducting planes. The low and intermediate field ϱ c ( T) curves can be fitted with a model, which takes into account the parallel conduction channels arising from intrinsic Josephson coupling and quasiparticle tunneling between the layers. At the highest measured fields, Josephson coupling between the layers is suppressed and the ϱ c ( T) dependence is parabolic.

Dielectric and transport properties of magnetic insulators irradiated with GeV heavy ions

The dielectric and ac/dc transport properties of single crystals of yttrium iron garnet (Y3Fe5O12 and Y3Fe5O12:Si), and barium hexaferrite (BaFe12O19 and BaFe12O1 9:Co,Ti) were investigated after irradiations with Xe and Pb ions in the GeV range. In the virgin n-type samples (Y3Fe5O12:Si and BaFe12O19:Co,Ti), the strong dielectric relaxation below 100 kHz is found to correspond to a space-charge polarization at the blocking metal/insulator contacts yielding a nonohmic dc conductivity. The relaxation frequency decreases with increasing amorphization yield in relation to the decrease of the insulators bulk dc conductivity which becomes ohmic in the amorphous phases. The ac conductivity data of both crystalline and amorphous Y3Fe5O12:Si above 100 kHz and for 100 K<T<300 K exhibit two contributions: (i) that of carrier transport in a disordered or inhomogeneous medium varying as νs, with s≃0.8, (ii) and that of a two-site polaron hopping process of charge transfer between Fe2+ and Fe3+ with an activation energy of 0.29 eV for T>180 K. The dc conductivity data of crystalline Y3Fe5O12:Si for 80 K<T<300 K are discussed on the basis of a small polaron hopping conduction mechanism between Fe2+ and Fe3+ with an activation energy around 0.28 eV for T>125 K, in agreement with the activation energy around 0.28 eV of the space-charge dielectric relaxation frequency for T>180 K. All amorphous phases data are consistent with the picture of hopping conduction between gap states in a disordered medium with (i) an νs dependence for the ac conductivity above a critical frequency proportional to the dc conductivity, (ii) and an exp(−T−1/4) law for the dc conductivity.

Thermopower, Electrical and Hall Conductivity of Undoped and Doped Iron Disilicide Single Crystals

AbstractThe electrical transport properties of β-FeSi2 single crystals have been investigated in dependence on the purity of the source material and on doping with 3d transition metals. The transport properties included are electrical conducticvity, Hall conductivity and thermopower mainly in the temperature range from 4K to 300K. The single crystals have been prepared by chemical transport reaction in a closed system with iodine as transport agent. In undoped single crystals prepared with 5N Fe both electrical conductivity and thermopower depend on the composition within the homogeinity range of β-FeSi2 which is explained by different intrinsic defects at the Sirich and Fe-rich phase boundaries. In both undoped and doped single crystals impurity band conduction is observed at low temperatures but above 100K extrinsic behaviour determined by shallow impurity states. The thermopower shows between 100K and 200K a significant phonon drag contribution which depends on intrinsic defects and additional doping. The Hall resistivity is considered mainly with respect to an anomalous contribution found in p-type and n-type single crystals and thin films. In addition doped single crystals show at temperatures below about 130K an hysteresis of the Hall voltage. These results make former mobility data uncertain. Comparison will be made between the transport properties of single crystals and polycrystalline material.

Electrical resistivity and hall effect of single crystal HgBa 2Ca 3Cu 4O 10+σ

We report the first measurements of the in-plane transport properties of single crystals of the four-layer superconductor HgBa 2Ca 3Cu 4O 10+σ with a transition temperature of 130 K. In the normal state the temperature dependence of the electrical resistivity and the Hall coefficient indicates that these crystals are underdoped. For the cotangent of the Hall angle we found a T 2 dependence. In the mixed state, the following form holds for a universal correlation between hall resistivity ϱ H and electrical resistivity ϱ: ϱ H ≈ ϱ n , with n = 1.75.

Electrical transport properties of single crystal HgBa 2Ca 3Cu 4O 10+ δ

We report the first measurements of the in-plane transport properties of single crystals of the four-layer superconductor HgBa 2Ca 3Cu 4O 10+δ with a transition temperature of 130 K. In the normal state the temperature dependence of the electrical resistivity and the Hall coefficient indicates that these crystals are underdoped. For the cotangents of the Hall angle we found a T 2 dependence.

Magnetic properties of single crystal TbNi 2B 2C

Magnetic and transport properties of single crystals of TbNi 2B 2C have been investigated by AC susceptibility, DC magnetisation and resistance measurements. The AC susceptibility and low field DC susceptibility data contain peaks corresponding to two magnetic transitions, one due to the magnetic ordering of Tb moments at 15 K and another at lower temperature ( T=5.1 K) due to a spin reorientation. As the applied magnetic field is increased, the low temperature transition is suppressed. The electrical resistance measurements show a sharp decrease in the resistance at 15 K but contain no observable features corresponding to the lower transition. Our resistance measurements show that TbNi 2B 2C does not become superconducting above 300 mK.

Thermal and electrical transport properties of single crystals

Electrical conductivity, Hall effect and thermoelectric power measurements are made for the compound . This compound, which is a semiconductor grown in a single-crystal form, is studied over a wide range of temperature from 150 to 375 K. The crystal is grown by a modification of the Bridgman method. The combination of the electrical and thermal measurements in the present investigation makes it possible to find various physical parameters and to reveal the general behaviour of this semiconductor.

Anisotropic magnetic properties of TbNi2B2C single crystals.

Magnetic and transport properties of single crystals of ${\mathrm{TbNi}}_{2}$${\mathrm{B}}_{2}$C have been investigated by ac susceptibility, dc magnetization, specific heat, and resistance measurements. The compound shows highly anisotropic magnetic properties which come about as a result of the Tb magnetic moments lying predominantly in the ab plane. The ac susceptibility and low-field dc magnetization measurements indicate the presence of two magnetic transitions; one due to the antiferromagnetic (AFM) ordering of the Tb moments around 15 K, and another at 5 K, which we believe is due to a spin reorientation of the Tb moments. The resistivity (${\mathrm{\ensuremath{\rho}}}_{\mathit{ab}}$) measurements show a sharp decrease in the resistance at 15 K but contain no observable features corresponding to the lower-temperature transition. The compound does not show superconductivity above 300 mK. Specific heat at low temperatures shows a large \ensuremath{\lambda}-type anomaly at 13.8 K in addition to the anomalies associated with the AFM ordering of the Tb moments at 15 K (${\mathit{T}}_{\mathrm{AF}}$) and the spin reorientation at 5 K. Magnetization (M) and ${\mathrm{\ensuremath{\rho}}}_{\mathit{ab}}$(T) measurements indicate a decrease in ${\mathit{T}}_{\mathrm{AF}}$ as a function of applied field (H) for H\ensuremath{\parallel}ab, whereas for H\ensuremath{\parallel}c, ${\mathit{T}}_{\mathrm{AF}}$ is independent of field. The M-H isotherms at 2 K show that for H\ensuremath{\parallel}ab the compound goes through a series of temperature-dependent metamagnetic states before finally saturating into a ferromagnetic state for H\ensuremath{\gtrsim}21 kOe. For H\ensuremath{\parallel}c the compound shows a linear M-H behavior expected for a normal AFM compound. The ${\mathrm{\ensuremath{\rho}}}_{\mathit{ab}}$(H) measurements show anomalies due to the metamagnetic transitions and a large negative magnetoresistance above 21 kOe for H\ensuremath{\parallel}ab. \textcopyright{} 1996 The American Physical Society.

Transport properties of single-crystal HgBa 2Ca 2Cu 3O 8+δ

We report the first measurements of the transport properties of single crystals of HgBa 2Ca 2Cu 3O 8+τ. Data for the in-plane and out-of-plane resistivity, in-plane Hall coefficient and in-plane thermoelectric power of single crystals with onset temperatures as high as 134 K are presented. The in-plane resistivity, Hall coefficient and thermoelectric power all indicate that these crystals are underdoped, which may offer at least a partial explanation for the strong pressure dependence of T c observed in this compound. The in-plane Hall coefficient shows a strong temperature dependence in accord with other cuprate superconductors. A calculation of the cotangent of the Hall angle (cotθ H) reveals that the relation cot θ H = AT 2 + B is obeyed to high precision in these crystals, despite strong curvature of the in-plane resistivity. Data are also reported for the influence of magnetic field on the resistive transition, for fields of up to 7 T applied both parallel and perpendicular to the crystallographic c-axis. These latter measurements give an estimate for the anisotropy of H c2, implying a value which is intermediate between that found for YBa 2Cu 3O 7−τ and Bi 2Sr 2CaCu 2O 8+ x .

Thermal transport properties of D-Er2Si22O7 at room temperature

The compound Er2Si2O7 exists in three modifications-a triclinic low-temperature phase (type B), a monoclinic modification (type C) and a high-temperature monoclinic modification (type D). The thermal transport properties of single crystals of D-Er2Si2O7 have been measured by the transient hot strip method. The average thermal conductivity was found to be about 1 W m-1 K-1. By using the calorimetric method the heat capacity per unit mass of D-Er2Si2O7 at room temperature was found to be 0.52+or-0.04 J g-1 K-1, corresponding to the molecular heat capacity of 31.4 R. The calculated molecular heat capacity at room temperature is 33 R.

Superconductivity in polycrystalline pressed pellets of k-(BEDT-TTF) 2I 3

Investigations of the transport properties of single crystals and polycrystalline pressed samples of k-(BEDT-TTF) 2I 3 are presented. In contrast to polycrystalline pressed samples of k-(BEDT-TTF) 2Cu(NCS) 2 and k-(BEDT-TTF) 2Cu[N(CN) 2]Br those of k-(BEDT-TTF) 2I 3 show bulk superconductivity indicating that the loss of superconductivity in the first two types of samples is not due to the special structure of the k-phase, but probably due to a disproportionation of Cu 1+ under the anisotropic pressure during the preparation of the samples. Annealing the single crystals as well as the polycrystalline pressed samples of k-(BEDT-TTF) 2I 3 at 75°C for a few days results in a structural transformation with an increase in the transition temperature for superconductivity (about 8K for the crystals). IR-spectra indicate a transformation into a structure which is identical with α t-(BEDT-TTF) 2I 3, which seems to be the thermodynamically most stable phase of the several (BEDT-TTF) 2I 3 phases.

Some transport properties of single crystals of group Va transition metal disilicides

Although transition metal disilicides are used in the form of thin films, single crystals are needed to study their intrinsic properties. Single crystals of Group Va transition metal disilicides, namely VSi 2, NbSi 2 and TaSi 2, have been successfully grown by Czochralski pulling from a levitated melt. The good quality of our crystals is shown by the high residual resistance ratios (VSi 2: RRR 20; NbSi 2: RRR 220; TaSi 2: RRR 400). The three compounds crystallize in the same hexagonal structure (C40, space group P6 222). Crystallographic and temperature dependences of the resistivity and of the magnetoresistance ( H ⊥ ⩽ 7.4 T) have been measured from 4.2 K up to room temperature. All the three materials show a metallic behaviour and some anisotropy, which is of the order of 2 for the three compounds. The magnetoresistance measurements show that VSi 2 and TaSi 2 are compensated metals with relatively small charge carrier concentrations (VSi 2: n ≈ 0.15 electrons/formula unit; TaSi 2: n ≈ 0.20–0.25 electrons/formula unit).