Low-temperature Resistivity Measurements Research Articles

Electronic transport in reactively sputtered Mn3GaN films prepared under optimized nitrogen flow

Abstract Mn-based nitrides with antiperovskite structures have several properties that can be utilized for antiferromagnetic spintronics. Their magnetic properties depend on the structural quality, composition and doping of the cubic antiperovskite structure. Such nitride thin films are usually produced by reactive physical vapor deposition, where the deposition rate of N can only be controlled by the N2 gas flow. We show that the tuning of the N content can be optimized using low temperature resistivity measurements, which serve as an indicator of the degree of structural disorder. Several Mn3GaN x films were prepared by reactive magnetron sputtering under different N2 gas flows. Under optimized gas flow conditions, we obtain films that exhibit a metal-like temperature dependence of the resistivity, a vanishing logarithmic increase of the resistivity towards zero, the highest resistivity ratio, and a lattice contraction of 0.4% along the growth direction when heated above the Néel temperature T N . The retarded formation of an additional magnetic phase appearing at a temperature T ∗ ≪ T N gives rise to a large thermal hysteresis of the resistivity and anomalous Hall effect.

Effect of transition metals on the crystal field in CeCo0.4Fe0.6Ge3

We present an investigation of the influence of the 3d elements, Co and Fe, on the interactions between magnetic Ce atoms in the CeCo0.4Fe0.6Ge3 alloy, the member of the CeCo1−xFexGe3 series. The investigated alloy crystallizes in the noncentrosymmetric tetragonal BaNiSn3-type structure (space group I4mm, No. 107), in which the Co and Fe atoms occupy the same 2a position. The close vicinity to the quantum critical point for this alloy was indicated based on previous reports and confirmed by our low temperature resistivity measurements presented in this article. The role of Co and Fe atoms in this alloy was deduced from the scheme of the crystal field levels employing inelastic neutron scattering, specific heat, and magnetic susceptibility. For the analysis, samples LaCoGe3, LaFeGe3, and LaCo0.4Fe0.6Ge3 were used as non-magnetic analogs. The obtained results for CeCo0.4Fe0.6Ge3 alloy were compared with those for CeCoGe3 and CeFeGe3 compounds to emphasize the observed changes in physical properties. The specific heat results are supported by the first-principles calculations. The analysis indicated that the excitation levels of Ce ions are different for the Co- and Fe-rich neighborhood. Based on this information, we can conclude that the 3d elements provide the same energies of RKKY and Kondo interactions for the nearest Ce ions, but their energies for the further ions are lowered due to the presence of other 3d elements.

Structural and electronic phase transitions in Zr1.03Se2 at high pressure

We have carried out a detailed high pressure investigation using x-ray diffraction, Raman spectroscopy, and low temperature resistivity measurements on 1T ${\mathrm{ZrSe}}_{2}$ having an excess of 3 at.% Zr. A careful x-ray diffraction data analysis shows that the sample undergoes a gradual structural transition to a monoclinic structure, with a mixed phase in the pressure range of 5.9 GPa to 14.8 GPa. We observe a minimum in the $c/a$ ratio as well as in the full width at half maximum of the ${A}_{1g}$ Raman mode at the same pressure in the parent 1T phase, which indicates an electronic phase transition. The sample shows a metallic characteristic in its low temperature resistivity data at ambient pressure, which persist until about 5.1 GPa and can be related to the presence of slight excess Zr. At and above 7.3 GPa, the sample shows a metal to semiconductor transition with the opening of a very small band gap, which increases with pressure. The low temperature resistivity data show an upturn, which flattens with the increase in pressure. The phenomenological analysis of the low temperature resistivity data indicates the presence of the Kondo effect in the sample, which may be due to the excess Zr.

Discovery of superconductivity in Nb4SiSb2 with a V4SiSb2-type structure and implications of interstitial doping on its physical properties.

We report on the discovery, structural analysis, and the physical properties of Nb4SiSb2 – a hitherto unknown compound crystallizing in the V4SiSb2-type structure with the tetragonal space group I4/mcm and unit cell parameters a = 10.3638(2) Å and c = 4.9151(2) Å. We find Nb4SiSb2 to be a metal undergoing a transition to a superconducting state at a critical temperature of Tc ≈ 1.6 K. The bulk nature of the superconductivity in this material is confirmed by the observation of a well defined discontinuity in specific heat with a normalized specific heat jump of ΔC(Tc)/γTc = 1.33 mJ mol−1 K−2. We find that for Nb4SiSb2, the unoccupied sites on the 4b Wyckoff position can be partially occupied with Cu, Pd, or Pt. Low-temperature resistivity measurements show transitions to superconductivity for all three compounds at Tc ≈ 1.2 K for Nb4Cu0.2SiSb2, and Tc ≈ 0.8 K for Nb4Pd0.2SiSb2 as well as for Nb4Pt0.14SiSb2. The addition of electron-donor atoms into these void positions, henceforth, lowers the superconducting transition temperature in comparison to the parent compound.

Polaron hopping conduction mechanism and magnetic properties of Pb‐doped LaMnO3

AbstractIn the present work, we have synthesized La1‐xPbxMno3 (0 ≤ x ≤ 0.20) perovskites through a conventional solid‐state reaction route. The powder x‐ray diffraction data analyzed through the Rietveld refinement program confirm monophase rhombohedral distorted structure (R‐3c space group). Fourier transform infrared spectra exhibit strong and well‐defined absorption bands of a typical perovskite structure. The x‐ray photoelectron spectroscopy studies confirm the elemental composition and oxidation state of various elements in the samples. Low temperature resistivity measurements do not reveal metal–semiconductor transition (MST) in the pristine sample while Pb‐doped samples show MST. The metallic region of the temperature‐dependent resistivity data is well fitted with ρ(T) = ρο + ρ2.5T2.5, which reveals the significance of electron–magnon interaction. Moreover, the semiconducting behavior of all the samples follows the Mott's variable range hopping conduction process. Additionally, the semiconducting part is also fitted with the small‐polaron hopping (SPH) model that establishes the non‐adiabatic SPH mechanism obeyed for the lower doping, whereas adiabatic mechanism for the higher Pb concentration. Magnetic studies clearly indicate a paramagnetic to weak ferromagnetic transition associated with the Pb doping that may be due to the double‐exchange mechanism between the manganese ions via oxygen orbitals. The outcomes are elucidated on the basis of substitution effect induced by Pb2+ ions.

Automated low-temperature resistivity measurement setup: Design and fabrication

In this paper we present, the design and working of the automated low-temperature four-probe DC electrical resistivity measurement setup developed in-house. This setup measures the resistance/resistivity in the temperature range 300 K to 80 K. The overall arrangement comprises a low-temperature four-probe sample holder, Lakeshore 335 Temperature controller, Keithley Delta mode 6221 AC/DC source, 2182A Nano-voltmeter, and a vacuum system. For the measurement of sample temperature Pt-100 sensor is employed. The IEEE-488.2 card and GPIB cables link the mentioned instruments to the computer. The licenced Lab-VIEW 2018 software is employed to build the control programme. The established setup can measure the resistance of both bulk and thin-film samples, making it versatile. A test measurement on well-characterized ceramic Pr0.67Sr0.33MnO3 perovskite oxide synthesized using a solid-state route has been carried out in the newly installed setup. The data acquired from the installed setup and beforehand resistance measurement carried out in-house low-temperature resistance measurement setup at UGC-DAE-Consortium for scientific research, Indore conceded a precision for both temperature and resistance.

N concentration effects on structure and superconductivity of NbN thin films

In this work, we present a study on niobium nitride (NbN) thin films deposited using a reactive magnetron sputtering of Nb at different partial pressures of N2 (RN2). The effect of N concentration on the structural and superconducting properties of niobium mononitride (NbN) thin films was investigated using x-ray diffraction and resistivity measurements. During the initial nitridation process (RN2 = 0.5 to 2%) N atoms occupy interstitial sites within Nb, leading to an expansion and distortion in Nb lattice. At an intermediate RN2 range (RN2 = 8 to 16%), nearly stoichiometric NbN phase emerges and further nitridation (RN2 = 20 to 100%) results in expansion and distortion of NbN, similar to the effect observed in Nb. Low temperature and high magnetic field resistivity measurements reveal that the superconducting transition temperature (TC) and the upper critical field (HC2(0)) maximizes to 12.8 K and 30 T at RN2 = 16%. Both deficiency or excess of N from equiatomic NbN composition leads to a reduction in TC and HC2(0). The effect of an applied radio frequency (rf) bias during the growth of NbN thin films was also studied and it was found that under optimized rf biasing conditions, the adatom mobility can be enhanced leading to superior long-range crystalline ordering with reduced disorder/defects. As a result, higher value of TC = 13.2 K was obtained. In essence through this work, we demonstrate possibilities to attain a stoichiometric NbN phase without the need of high growth temperatures during the deposition process.

Investigation of Structural, Optical and Electrical Transport Properties of Yttrium Doped La0.7Ca0.3MnO3 Perovskites

In the present study, bulk samples of yttrium doped La0.7−xYxCa0.3MnO3 (x = 0.3 and 0.4) are prepared through solid-state reaction route. The structural, optical and electrical transport properties have been explored through various analytical techniques. The x-ray diffraction (XRD) patterns affirm single phase and polycrystalline nature of the samples. Rietveld refinement analysis of the XRD data is used to determine the various structural parameters. It reveals that both the samples belong to orthorhombic crystal system with Pnma space group. Using Scherrer’s equation, a lower value of crystallite size is found in the higher concentration of yttrium doped sample. The band gap as determined from the UV–visible DRS data by employing the Tauc’s relation is found to enhance with the increase of yttrium concentration in La0.7Ca0.3MnO3. The low temperature resistivity measurements establish semiconducting nature of the samples over the temperature range of ~ 110–300 K. Moreover, the electrical resistivity data are interpreted within the variable range hopping (VRH) model to estimate the density of states at the Fermi level N(EF), mean hopping distance Rh(T) and hopping energy Eh(T). It is observed that the electrical quantities vary gradually with the change of Y content. The conduction mechanism in this system is governed in the framework of thermally activated small polaron hopping (SPH) model and accordingly various parameters namely Debye temperature (θD), activation energy (Ep) and optical phonon frequency (νph) are evaluated. The obtained results support a strong connection between structure and electrical behavior in our samples and can be elucidated on the basis of localization of charge carriers induced by the substituting ions.

Chemical and structural stability of superconducting In5Bi3 driven by spin–orbit coupling

Relativistic effects play a prominent role in many electronic material properties such as the Rashba and Dresselhaus spin splitting in inversion asymmetric crystals, or the bulk band gap in topological insulators. By contrast, macroscopic material properties are typically not connected to relativistic phenomena. As an exception to this rule, we show that the macroscopic chemical and structural properties of superconducting In5Bi3 are driven by relativistic physics. In the non-relativistic limit In5Bi3 decomposes into elemental indium and bismuth, but the inclusion of relativistic spin–orbit coupling chemically stabilizes the In5Bi3 stoichiometry. Similarly, the structural stability of tetragonal In5Bi3 is driven by the spin–orbit interaction, which eliminates a phonon instability present in the non-relativistic limit. Low-temperature resistivity and heat capacity measurements show that In5Bi3 is a strong coupling superconductor, with a superconducting critical temperature of 4.2 K and a superconducting critical field of 0.3 T. The unconventional interplay between relativity with chemistry and structure, together with the presence of superconductivity, make In5Bi3 a versatile material that provides, for example, a simple model for the study of strong coupling superconductivity in quasiperiodic crystals.

Phase Stability and Compressibility of 3R-MoN2 at High Pressure

We report phase stability and compressibility of rhombohedral 3R-MoN2, a newly discovered layer-structured dinitride, using in-situ synchrotron high-pressure x-ray diffraction measurements. The obtained bulk modulus for 3R-MoN2 is 77 (6) GPa, comparable with that of typical transition-metal disulfides (such as MoS2). The axial compressibility along a axis is more than five times stiffer than that along c axis. Such strong elastic anisotropy is mainly attributed to its layered structure with loosely bonded N-Mo-N sandwich interlayers held by weak Van der Waals force. Upon compression up to ~15 GPa, a new hexagonal phase of 2H-MoN2 occurs, which is irreversible at ambient conditions. The structural transition mechanism between 3R and 2H phases is tentatively proposed to be associated with the rotation and translation of sandwich interlayers, giving rise to different layer stacking sequences in both phases. At high temperature, the decomposition of 3R-MoN2 leads to the formation of hexagonal δ-MoN and the onset degassing temperature increases as the pressure increases. In addition, the low-temperature electrical resistivity measurement indicates that 3R-MoN2 behaves as a semiconductor with an estimated band gap of Eg ≈ 0.5 eV. 3R-MoN2 also shows weak antiferromagnetic properties, which probably originates from the occurrence of magnetic zigzag edges in the structure.

Investigation on the structure and physical properties of Fe3O4/RGO nanocomposites and their photocatalytic application

In the present work, we have investigated the structural, optical, photocatalytic activity, electrical transport and magnetic properties of Fe3O4 nanoparticles and its composite with reduced graphene oxide (Fe3O4/RGO) by varying the ratio of reduced graphene oxide (RGO: 2% and 4%). Fe3O4 nanoparticles and RGO were synthesized by the modified sol-gel and Hummers methods respectively. The as-prepared samples were examined by various analytical techniques to investigate their functional properties and possible applications. Rietveld refinement analysis of the XRD data reveals face-centered cubic (fcc) structure of the Fe3O4 nanoparticles and confirms the characteristic planes of magnetite phase. The average crystallite size of the Fe3O4, Fe3O4/RGO (2%) and Fe3O4/RGO (4%) samples was estimated using Scherrer's equation and found to be ∼10, 15 and 19 nm respectively. TEM/HRTEM micrographs establish spherical shapes of the magnetite nanoparticles with an average diameter of ∼12 nm for Fe3O4, while 17 and 20 nm in the nanocomposites respectively. The low temperature resistivity measurements exhibit semiconducting nature of all the samples and follow variable range hopping (VRH) mechanism. The magnetic measurements demonstrate typical superparamagnetic behavior of the samples at room temperature. The photocatalytic performance of the samples has been investigated for the decolorization of methylene blue (MB) organic dye under visible light irradiation. The Fe3O4/RGO nanocomposites display better adsorption behaviour and excellent photocatalytic activity than RGO and Fe3O4 nanoparticles. This may be due to strong interactions between Fe3O4 nanoparticles and graphene sheets.

Study on electrical behaviour of copper and its alloys containing dispersed nanoparticles

Nanoparticles can be added to metals to tune their properties for numerous applications. Recently extensive research has been conducted to measure the mechanical properties of nanoparticle reinforced metals. However, few theories exist to understand how nanoparticles interact with metals to affect their electrical performance, partly due to the difficulty in producing bulk metal samples, containing dispersed nanoparticles. In this work, copper and copper alloys (Cu, Cu-40 wt% Zn, and Cu-60 wt% Ag) containing dispersed tungsten carbide (WC) nanoparticles of more than 20 vol% were successfully fabricated via solidification processing. The experimental results show that copper and its alloys with an increasing volume fraction of nanoparticles, the electrical conductivity of the samples decays exponentially. Therefore, a theoretical model, compatible with the Nordheim's rule was established to predict the electrical behaviour of metals containing dispersed nanoparticles. This new model on the electrical behaviour of copper nanocomposites is experimentally validated by low-temperature resistivity measurements and electronic heat capacity measurements above Debye temperature.

Low temperature studies of Bi doped Pr0.6Sr0.4MnO3 manganites: magnetization and magneto-transport

Low temperature magnetization and resistivity measurements of bismuth (Bi) doped Pr0.6− xBixSr0.4MnO3 (x = 0.2, 0.23 and 0.25) manganites synthesized by solid state reaction method are reported here. Resistivity measurements in all bismuth doped samples in the absence of field show no significant metal–insulator transition. But for x = 0.2, in zero field the transition observed at lower temperature is associated with hysteresis indicating its first order nature. The resistivity and magnetization measurements establish the coexistence of ferromagnetic metallic and antiferromagnetic insulating phase at lower temperature. We present magnetization and resistivity measurements on higher concentration of bismuth exhibiting the coexistence of two phases at low temperature and the kinetic arrest of a first-order ferromagnetic-to-antiferromagnetic transition

Bound magnetic polaron driven room-temperature ferromagnetism in Ni doped ZnS nanoparticles

Magnetism in dilute magnetic semiconductors (DMSs) has been a controversial topic since its discovery. There are many models which predict the origin of room temperature ferromagnetism (RTFM) in TM doped wide band gap semiconductors. Here, we report RTFM in chemically synthesized cubic Zn1-xNixS (0 ≤ x ≤ 0.08) DMS nanoparticles of ∼3–5 nm size. Ferromagnetic behavior (at 300 K and 5 K) was found to increase with the increase in Ni doping concentration and was understood due to defect induced ferromagnetism. The low temperature magnetization measurement (ZFC-FC) shows that the nanoparticles are strongly coupled by magnetic interactions. Optical studies showed decrease in the energy bandgap along with the presence of sulfur and zinc vacancies and surface defects. Low temperature resistivity measurement depicted the semiconducting nature of the synthesized samples. With increase in doping concentration, an increase in the resistive behavior was observed which was explained in the realm of defects states created due to doping of the Ni ions.

In-field X-ray and neutron diffraction studies of re-entrant charge-ordering and field induced metastability in La0.175Pr0.45Ca0.375MnO3-δ

Low-temperature high-magnetic field (2 K, 8 T) (LTHM) powder X-ray diffraction (XRD) and time of flight powder neutron diffraction (NPD), low-temperature transmission electron microscopic (TEM), and resistivity and magnetization measurements have been carried out to investigate the re-entrant charge ordering (CO), field induced structural phase transitions, and metastability in phase-separated La0.175Pr0.45Ca0.375MnO3-δ (LPCMO). Low-temperature TEM and XRD studies reveal that on cooling under zero-field, paramagnetic Pnma phase transforms to P21/m CO antiferromagnetic (AFM) insulating phase below ∼233 K. Unlike reported literature, no structural signature of CO AFM P21/m to ferromagnetic (FM) Pnma phase-transition during cooling down to 2 K under zero-field was observed. However, the CO phase was found to undergo a re-entrant transition at ∼40 K. Neutron diffraction studies revealed a pseudo CE type spin arrangement of the observed CO phase. The low-temperature resistance, while cooled under zero-field, shows insulator to metal like transition below ∼105 K with minima at ∼25 K. On application of field, the CO P21/m phase was found to undergo field-induced transition to FM Pnma phase, which shows irreversibility on field removal below ∼40 K. Zero-field warming XRD and NPD studies reveal that field-induced FM Pnma phase is a metastable phase, which arise due to the arrest of kinetics of the first-order phase transition of FM Pnma to CO-AFM P21/m phase, below 40 K. Thus, a strong magneto-structural coupling is observed for this system. A field-temperature (H-T) phase-diagram has been constructed based on the LTHM-XRD, which matches very nicely with the reported H-T phase-diagram constructed based on magnetic measurements. Due to the occurrence of gradual growth of the re-entrant CO phase and the absence of a clear structural signature of phase-separation of CO-AFM P21/m and FM Pnma phases, the H-T minima in the phase-diagram of the present LPCMO sample has been attributed to the strengthening of AFM interaction during re-entrant CO transition and not to glass like “dynamic to frozen” transition.

Superconductivity in [formula omitted] compounds ([formula omitted]= d-electron transition metal)

Polycrystalline samples of YTE2Ge2 with TE= Co, Ni, Ru, Rh, Pd and Pt were synthesized and characterized by means of X-ray powder diffraction and low-temperature electrical resistivity and specific heat measurements, supplemented by fully relativistic full-potential local-orbital band structure calculations. We confirm that most of the compounds studied crystallize in a body-centered tetragonal ThCr2S2-type structure (space group I4/mmm) and have three-dimensional Fermi surfaces, while only one of them (YPt2Ge2) forms with a primitive tetragonal CaBe2Ge2-type unit cell (space group P4/nmm) and possesses quasi-two-dimensional Fermi surface sheets with some nesting. Physical properties data show conventional superconductivity in the phases with TE= Co, Pd and Pt, i.e. independently of the structure type (and hence the dimensionality of the Fermi surface).

Superconductivity in single crystalline YPd2Ge2

Single crystals of the YPd2Ge2 compound, crystallizing in the body-centered tetragonal ThCr2Si2-type structure, were studied by means of low-temperature magnetization, specific heat and electrical resistivity measurements. The zero-field data confirmed bulk and intrinsic superconductivity of the compound with the critical temperature 1.14 K, while the experiments performed in magnetic fields revealed a non-trivial character of the superconducting state. In particular, low and close to each other critical fields μ0Hc1 and μ0Hc2 (of about 20–30 mT) and field-induced first-order phase transition occurring only in the field parallel to the ab plane suggest possible cross-over from the type-I to type-II/1 superconductivity. Moreover, YPd2Ge2 exhibits robust surface superconductivity with the critical field μ0Hc3 about 20 times larger than μ0Hc1 and μ0Hc2.

Polaronic transport in Ag-based quaternary chalcogenides

Low temperature resistivity measurements on dense polycrystalline quaternary chalcogenides Ag2+xZn1-xSnSe4, with x = 0, 0.1, and 0.3, indicate polaronic type transport which we analyze employing a two-component Holstein model based on itinerant and localized polaron contributions. Electronic structure property calculations via density functional theory simulations on Ag2ZnSnSe4 for both energetically similar kesterite and stannite structure types were also performed in order to compare our results to those of the compositionally similar but well known Cu2ZnSnSe4. This theoretical comparison is crucial in understanding the bonding that results in polaronic type transport for Ag2ZnSnSe4, as well as the structural and electronic properties of both crystal structure types. In addition to possessing this unique electronic transport, the thermal conductivity of Ag2ZnSnSe4 is low and decreases with increasing silver content. This work reveals unique structure-property relationships in materials that continue to be of interest for thermoelectric and photovoltaic applications.

Structural and Electrical Properties Characterization of Sb1.52Bi0.48Te3.0 Melt-Spun Ribbons

Melt-spinning (MS) has been reported as a promising tool to tailor the microstructure of bulk thermoelectric materials leading to enhanced thermoelectric performances. Here, we report on a detailed characterization of p-type Bi0.48Sb1.52Te3 ribbons produced by melt-spinning. The microstructure of the melt-spun ribbons has been studied by means of X-ray diffraction, scanning and transmission electron microscopy (TEM). The analyses indicate that the ribbons are highly-textured with a very good chemical homogeneity. TEM reveals clear differences in the microstructure at large and short-range scales between the surface that was in contact with the copper wheel and the free surface. These analyses further evidence the absence of amorphous regions in the melt-spun ribbons and the precipitation of elemental Te at the grain boundaries. Low-temperature electrical resistivity and thermopower measurements (20–300 K) carried out on several randomly-selected ribbons confirm the excellent reproducibility of the MS process. However, the comparison of the transport properties of the ribbons with those of bulk polycrystalline samples of the same initial composition shows that MS leads to a more pronounced metallic character. This difference is likely tied to changes in deviations from stoichiometry due to the out-of-equilibrium conditions imposed by MS.

Structural, transport and magnetotransport properties of Ru-doped La0.5Sr0.5Mn1−xRuxO3 (x = 0.0 & 0.05) manganite

We report the results of the structural, transport and magnetotransport studies on polycrystalline La0.5Sr0.5Mn1−xRuxO3 (x = 0.0 and 0.05) manganite investigated using XRD and resistivity (with and without field) measurements. Rietveld refinement of XRD patterns confirms the single phasic tetragonal structure for both the samples crystalizing in I4/mcm space group (No. 140). Low-temperature resistivity and MR measurements with H = 0T & 5T field show thermal hysteresis which has been attributed to the first order phase transition. The increase in resistivity and decrease in metal – insulator transition temperature (TMI) with Ru – doping concentration in La0.5Sr0.5MnO3 (LSMO) has been understood in the context of superexchange interaction between Mn and Ru ions. The observed upturn in resistivity at low temperature under field has been explained using combined effect of electron – electron (e - e) interaction, Kondo-like spin-dependent scattering and electron – phonon interaction while the variation in resistivity at high temperature (T > Tp) has been explained using adiabatic small polaron hopping model.