Electrical resistivity of PdHx: I. Residual resistivity

Results are presented for the electrical resistivity of PdH_x alloys at several fixed temperatures. The residual resistivity goes through a maximum at x = 0.73 and then drops sharply as x approaches 1. From this we conclude that the residual resistivity for 0.8 < x < 1 is due primarily to vacancies in the hydrogen lattice and that the hydrogen atoms occupy only the octahedral sites of the Pd lattice. The absolute values of the residual resistivity are in reasonable agreement with theoretical expectations.     

Electrical resistivity of narrow-band ferromagnetic Fe1−xCoxS2

The electrical resistivity of metallic ferromagnet Fe_1−xCo_xS₂ shows an anomalous temperature dependence below Curie point. As the temperature lowers, the resistivity increases for x < 0.9, while it decreases for x > 0.9 with a hump.     

Low temperature resistivity minimum and its correlation with magnetoresistance in La0.67Ba0.33MnO3 nanomanganites

A systematic investigation of structural, magnetic and electrical properties of nanocrystalline La_0.67Ba_0.33MnO₃ materials, prepared by citrate gel method has been undertaken. The temperature-dependant low-temperature resistivity in ferromagnetic metallic (∼50 K) phase shows upturn behavior and is suppressed with applied magnetic field. The experimental data (<75 K) can be best fitted in the frame work of Kondo-like spin-dependant scattering, electron-electron and electron-phonon interactions. It has been found that upturn behavior may be attributed to weak spin disorder scattering including both spin polarization and grain boundary tunneling effects, which are the characteristic features of extrinsic magnetoresistance behavior, generally found in nanocrystalline manganites. The variation of electrical resistivity with temperature in the high temperature ferromagnetic metallic part of electrical resistivity (75K<T<T_P) has been fitted with grain/domain boundary, electron-electron and magnon scattering mechanisms, while the insulating region (T>T_P) of resistivity data has been explained based on adiabatic small polaron hopping mechanism.     

The transport properties in Nd0.75Sr1.25CoO4 film: Evidence for polaronic transport

The experiments of electrical resistivity and thermopower on Nd_0.75Sr_1.25CoO₄ film in the temperature range 90 K<T<310 K were carried out. The great difference in the activation energies estimated from thermopower and resistivity, a characteristic of small polarons, is observed, providing strong evidence for polaron-dominated transport mechanism in this material. Furthermore, the activation energy at intermediate-temperature region is larger than that at low-temperature region in resistivity, but it is not observed in thermopower, indicating that the energy for the creation of the carriers is slightly lower at low-temperature region than that at intermediate-temperature region. At the same time, the abrupt drop in the thermopower and the abnormal peak in the differential curve of resistivity indicate that a phase transition between a paramagnetic state and a ferromagnetic state occurs at temperature about 218 K. The positive thermopower in the whole temperature range measured suggests that the carriers are holes in this system.     

C-axis thermoelectric transport in low stage SbCl5 graphite intercalation compounds

c-axis thermal conductivity, electrical resistivity and thermopower measurements performed on stages-2, 3 and 4 SbCl₅-graphite intercalation compounds in the temperature range 3 < T < 300 K are reported. Contrary to the electrical resistivity and thermopower data, the temperature variation of the thermal conductivity is qualitatively different from that previously observed on other intercalation compounds.     

Electrical conductivity and low field magnetoresistance in polycrystalline La1−xKxMnO3 pellets prepared by pyrophoric method

Electrical conductivity and magnetoresistance of a series of monovalent (K) doped La_1−xK_xMnO₃ polycrystalline pellets prepared by pyrophoric method have been reported. K doping increases the conductivity as well as the Curie temperature (T_C) of the system. Curie temperature increases from 260 to 309 K with increasing K content. Above the metal-insulator transition temperature (T>T_MI), the electrical resistivity is dominated by adiabatic polaronic model, while in the ferromagnetic region (50<T<T_MI), the resistivity is governed by several electron scattering processes. Based on a scenario that the doped manganites consist of phase separated ferromagnetic metallic and paramagnetic insulating regions, all the features of the temperature variation of the resistivity between ∼50 and 300 K are described very well by a single expression. All the K doped samples clearly display the existence of strongly field dependent resistivity minimum close to ∼30 K. Charge carrier tunneling between antiferromagnetically coupled grains explains fairly well the resistivity minimum in monovalent (K) doped lanthanum manganites. Field dependence of magnetoresistance at various temperatures below T_C is accounted fairly well by a phenomenological model based on spin polarized tunneling at the grain boundaries. The contributions from the intrinsic part arising from DE mechanism, as well as, the part originating from intergrannular spin polarized tunneling are also estimated.     

Scattering of charge carriers on a high spin-low spin mixture in MnAs1−xPx crystals

The specific resistivity anomaly between the magnetic ordering temperature T_N and the displacive phase transition temperature T_t of MnAs_1?xP_x crystals with 0.03 < x < 0.15 seems to be connected with the existence of a high spin-low spin mixture which has been inferred recently from specific heat data.     

Magnetotransport properties of epitaxial Pr0.5Ca0.5MnO3 films grown by a solution technique

Epitaxial Pr_0.5Ca_0.5MnO₃ films have been synthesized on (0 0 1) SrTiO₃ substrate using a chemical solution deposition technique and two-step post-annealing process. The zero field resistivity of the films shows semiconducting behavior and a characteristic of charge ordering is observed at 230 K. The resistivity of the 10 nm film did not show any effect with the magnetic field. However, melting of charge ordering was observed for the 120 nm film at an applied magnetic field of 4 T. Large decrease in the resistivity of the 120 nm film (<100 K) resulted in magnetoresistance of nearly −100% at 75 K.     

On the coexistence of spin and lattice polarons in the La0.67−xEuxCa0.33MnO3 CMR system

The electrical and magnetic transport properties of the La_0.67−xEu_xCa_0.33MnO₃ system exhibit lowering of insulator to metal and paramagnetic to ferromagnetic transition temperature (T_C) with the increase of Eu concentration in addition to possessing CMR property. The temperature variation of electrical resistivity and magnetic susceptibility for x=0.21 is found to have two distinct regions in the paramagnetic state for T>T_P; one with the localization of lattice polaron in the high-temperature region (T>1.5T_P) satisfying the dynamics of variable range hopping (VRH) model and the other being the combination of the spin and lattice polarons in the region T_P<T<1.5T_P. The resistivity variation with temperature and magnetic field, the cusp in the resistivity peak and CMR phenomenon are interpreted in terms of coexistence of spin and lattice small polarons in the intermediate region (T_P<T<1.5T_P). The spin polaron energy in the La_0.46Eu_0.21Ca_0.33MnO₃ system is estimated to be 106.73±0.90 meV and this energy decreases with the increase of external magnetic field. The MR ratio is maximal with a value of 99.99% around the transition temperature and this maximum persists till T→0 K, at the field of 8 T.     

Quantum critical behaviour in the CePd2Si2/CeNi2Ge2 system

We have explored the vicinity of the antiferromagnetic quantum critical point in the related heavy fermion metals CePd₂Si₂ and CeNi₂Ge₂ as a function of hydrostatic pressure. The normal state resistivity of the antiferromagnet CePd2Si2 near the critical pressure, at which magnetic order disappears, varies as ρ ～ T^χ(1:1 < χ < 1:4) over nearly two orders of magnitude in temperature up to about 30 K. This anomalous form for the resistivity appears to defy not only Fermi-liquid theory, but also simple phenomenological models for the effect of spin fluctuations close to a quantum critical point. An analogous unconventional behaviour is observed in the ambient pressure resistivity of the electronically and structurally equivalent, non-magnetic metal CeNi₂Ge₂. At pressures above 15 kbar, a new and unexpected superconducting transition appears in CeNi₂Ge₂ below 220 mK, which rises to higher temperatures with increasing pressure, reaching 400 mK at 26 kbar.     

A comparison of CeS and CeAl2

The compression curve (to 200 kbars) and the ambient resistivity versus temperature (1.5K <T < 300K) of CeS have been measured. The results are compared to the analogous experiments on the compound CeAl₂. A high pressure valence instability and ambient pressure crystalline electric field, spin fluctuation and magnetic order effects are found to be common to both compounds.     

Magnetic and electrical properties of cation-substituted sulfides MexMn1 ? xS (Me = Co, Gd)

The temperature dependences of the specific magnetization σ and the electrical resistivity ρ of Me _x Mn_{1 − x} S single crystals (Me= Co, Gd; x= 0.05) have been studied in the temperature range 80 K < T < 1000 K. The samples under study have revealed the presence of a spontaneous magnetic moment below the Néel temperature (T _N) and ferromagnetic clusters in Gd_0.05Mn_0.95S in the temperature range 146 K < T < 680 K. Substitution of gadolinium for manganese initiates a transition from p-type to n-type conduction. The change in the conduction type is accompanied by an increase in the electrical resistivity at 300 K by approximately one order of magnitude and, accordingly, by a decrease in the activation energy. The magnetic and electrical properties of the crystals under study have been interpreted in terms of the cluster model with temperature-dependent ferromagnetic exchange and an electron localized in this cluster. Original Russian Text ? S.S. Aplesnin, L.I. Ryabinkina, O.B. Romanova, V.V. Sokolov, A.Yu. Pichugin, A.I. Galyas, O.F. Demidenko, G.I. Makovetskiĭ, K.I. Yanushkevich, 2009, published in Fizika Tverdogo Tela, 2009, Vol. 51, No. 4, pp. 661–664.     

Transport properties of Sn1−xMnxTe at low magnetic field

Magnetic ordering and transport phenomena have been investigated in the system Sn_1?xMn_xTe for 0.02 < x < 0.08. The peak of resistivity is found at temperatures systematically lower than the Curie temperature, so that it cannot be imputed to a spin disorder scattering, contrary to previous interpretations. The data are analyzed in terms of a resonant scattering on a virtual bound level. An overall agreement is found between theory and experiment.     

Low-temperature transport properties of chemical solution deposited polycrystalline La0.7Sr0.3MnO3 ferromagnetic films under a magnetic field

Polycrystalline La_0.7Sr_0.3MnO₃ (LSMO) films were prepared on SiO₂/Si (001) substrates by chemical solution deposition technique. Electrical and magnetic properties of LSMO were investigated. A minimum phenomenon in resistivity is found at the low temperature (<50 K) under magnetic fields from 0 T to 3 T. Kondo-like spin dependent scattering, which includes both spin polarization and grain boundary tunneling, was observed in the low-temperature electrical transport for the LSMO polycrystalline films. The temperature-dependent resistivity at low temperatures can be well fitted in the framework of elastic scattering, electron-electron (e-e) interaction, Kondo-like spin dependent scattering, and electron-phonon (e-ph) interaction.     

Low temperature resistivities of FexNi80-xP14B6 metallic glasses

The resistivities of six Fe_xNi_80-xP₁₄B₆ alloys have been measured between 1.5 and 50 K. It is found that the resistivity variations both below and above the resistivity minima depend on the transition metal composition. The room temperature coefficients of the resistivity indicate the existence of the magnetic contribution to the resistivity.     

Effect of phase stratification into electro- and magnetotransport in heteroepitaxial La2/3Ca1/3MnO3 films

The La_2/3Ca_1/3MnO₃ films 25-nm thick biaxially compressed in the substrate plane, grown quasi-coherently on the (001) surface of the LaAlO₃ single crystal, were studied using laser vaporization. It was found that mechanical stresses acting during nucleation and growth promoted calcium enrichment of the cation sublattice of the manganite layer, which caused a decrease in its unit cell volume. Crystalline grains in manganite films were distinctly oriented along the normal to the substrate plane; the grain size in the substrate plane was within 20–40 nm, and the relative grain misorientation in the substrate plane did not exceed 0.2°. In zero magnetic field, the maximum in the temperature dependence of the resistivity ρ of La_2/3Ca_1/3MnO₃ films was observed at temperatures close to 210 K. At T < 100 K and μ₀ H = 2 T, the magnetoresistance of manganite films was negative, weakly depended on temperature, its value was about–0.45. The magnetic field caused transformation of nonferromagnetic phase inclusions to ferromagnetic ones, which resulted in a decrease in the La_2/3Ca_1/3MnO₃ film resistivity with increasing magnetic field. At low temperatures (T < 100 K), a hysteresis was observed in the dependences of the film resistivity on the magnetic field.     

非晶态(Fe1-xWx)84.5B15.5合金的低温电阻率反常

研究了(Fe_1-xW_x)_84.5B_15.5(x=0—0.1)非晶态合金的电阻率ρ与温度T(4.2—300K)的关系。实验结果表明,在所研究浓度区域内均出现电阻率与温度关系的极小值,电阻率极小值的温度T_min在x=0.06时出现峰值。用x=0.02—0.1浓度区域内,当Tmin时,又出现了电阻率与温度关系的极大值,电阻率极大值的温度T_max在26—35K之间。低温电阻率反常现象与类Kondo效应及局域磁矩之间RKKY相互作用有关。 关键词：     

Control of p-type conductivity in Sr doped LaTiO3 thin films

We report on in situ growth by pulsed laser deposition of Sr-doped LaTiO₃ (Sr, 0<x<0.1) thin films, with epitaxial c-axis perovskite structure. According to the increase of Sr doping, resistivity of samples decreases and films reveal metallic behaviour. We found that both crystallographic and electrical properties are very sensitive to oxygen pressure during the deposition. The charge carrier was found to be p-type for Sr doping from 0 to 10% and mobility is much higher than previously reported.     

Magnetic and electrical behavior of La1−xAxMnO3 (A=Li, Na, K and Rb) manganites

With a view to understand the magnetic and electrical behavior of monovalent substituted lanthanum manganites, a series of materials were prepared by sol-gel route by sintering at 1200 °C. The X-ray diffraction data were analyzed using Rietveld refinement technique and it has been found that all the samples were found to crystallize into rhombohedral structure with R3¯c space group. The values of ferro to paramagnetic (T_C) and metal-insulator transition (T_P) temperatures were obtained using ac susceptibility and electrical resistivity data, respectively. It has been found that sodium-, potassium- and rubidium-doped samples exhibit two peaks in the electrical resistivity vs. temperature plots. The observed behavior has been explained on the basis of oxygen deficiency present in the samples. The electrical resistivity data were analyzed using various theoretical models and it has been concluded that the electrical resistivity data in the low-temperature regime (T<T_P) can be explained using the equation ρ_(T)=ρ₀+ρ₂T²+ρ_4.5T^4.5, signifying the importance of the grain/domain boundary, electron-electron and two magnon scattering processes. On the other hand, the high-temperature resisitivity data (T>T_P) were explained using variable range and small polaron hopping mechanisms.     

The suppression of structural phase transformation in LaVO3 and La1−xSrxVO3 thin films fabricated by pulsed laser deposition

Highly oriented (100) thin films of LaVO₃ and La_1−xSr_xVO₃ have been fabricated by pulsed laser deposition in a reducing atmosphere. The films show a transition from insulating to metallic behaviour in the composition region of x, 0.175<x<0.200. In the single crystals of the antiferromagnetic insulating phase, a first-order structural phase transition is observed few degrees below the magnetic transition, which manifests itself as a kink in the temperature dependence of resistivity. In the highly oriented thin films of LaVO₃ and La_1−xSr_xVO₃ fabricated on lattice matched substrates in this study, the structural phase transformation in the insulating phase has been suppressed. The electrical conduction is found to take place via hopping through localized states at low temperatures. The metallic compositions show a non-linear (T^1.5) behaviour in the temperature dependence of resistivity. V (2p) core level spectra of these films show a gradual change in the relative intensities of V³⁺ and V⁴⁺ ions as the value of x increases.