Temperature Resistivity Minimum Research Articles

Transport properties and electroresistance of manganite based heterostructure

In the present communication, ZnO/La0.7Sr0.3MnO3/Al2O3 (ZnO/LSMO/Al2O3) heterostructure was grown using chemical solution deposition (CSD) technique. X–ray diffraction (XRD) measurement confirms the (100) crystallographic oriented growth of LSMO manganite and polycrystalline hexagonal growth of ZnO layer. Temperature dependent resistivity behavior under different applied magnetic fields, performed for two different geometries [current in plane (CIP) and current perpendicular to plane (CPP)], suggests the modifications in metal to insulator transition temperature TP and alterations in resistivity with applied magnetic field and measurement geometry. This also implies the better charge conduction across the ZnO/LSMO interface (CPP) as compared to LSMO film layer (CIP). Various charge conduction mechanisms have been employed to understand the charge transport for observed low temperature resistivity minimum, metallic behavior, insulating state and magnetoresistance (MR) of LSMO film and ZnO/LSMO interface. Electroresistance (ER) and field effect configuration (FEC) have been investigated across the ZnO/LSMO interface by recording the LSMO channel resistance, at room temperature, that suggest the tuning of signature and value of ER by considering forward and reverse bias modes across the interface. FEC studies show the large ER ∼ +750% and −85% across the LSMO channel with its tunability under different interface biases.

Magnetic and magnetoresistance in half-doped manganite La0.5Ca0.5MnO3 and La0.5Ca0.4Ag0.1MnO3

La0.5Ca0.5MnO3 and La0.5Ca0.4Ag0.1MnO3 ceramics have been prepared by sol–gel methods and its magnetic properties, and electronic transport properties have been experimentally investigated. X-ray diffraction data reveal that all samples crystallize in a orthorhombic structure with Pnma space group. Magnetic measurements of La0.5Ca0.5MnO3 show multiple magnetic transitions, a paramagnetic to ferromagnetic and a ferromagnetic to charge-ordered antiferromagnetic. Two metal–semiconductor transitions (Tρ1 and Tρ2) are observed in the electrical resistivity. The electrical resistivity decreases when an external magnetic field is applied rendering a magnetoresistive effect of the order of 75% at the charge-ordered temperature. All the samples clearly reveal the unusual low temperature resistivity minimum, presumably due to the combined effect of weak localization, electron–electron and electron–phonon scattering. The present results are discussed and possible explanations were given based on the related theory and previous reported results.

Kondo scattering inδ-dopedLaTiO3/SrTiO3interfaces: Renormalization by spin-orbit interactions

We present a study of delta ($\delta$) doping at LaTiO$_3$/SrTiO$_3$ (LTO/STO) interface with iso-structural antiferromagnetic perovskite LaCrO$_3$ (LCO) that dramatically alters the properties of the two dimensional electron gas (2-DEG) at the interface. The effects include a reduction in sheet-carrier density, prominence of the low temperature resistivity minimum, enhancement of weak antilocalization below 10 K and observation of a strong anisotropic magnetoresistance (MR). The positive and negative MR for out-of-plane and in-plane field respectively and the field and temperature dependencies of MR suggest Kondo scattering by localized Ti$^{3+}$ moments renormalized by spin-orbit interaction at T $<$ 10 K, with the increased $\delta$-layer thickness. Electron energy loss spectroscopy and density functional calculations provide convincing evidence for blocking of electron transfer from LTO to STO by the $\delta$-layer.

Electrical transport studies on the La0.7−xPrxBa0.3MnO3 (x=0, 0.1 and 0.2) manganite: Double metal–insulator transitions and low-temperature resistivity minimum

The electrical transport properties of the polycrystalline samples La0.7−xPrxBa0.3MnO3 (0≤x≤0.2) have been investigated. Two metal–insulator transitions (TP1 and TP2) are observed in the electrical resistivity. The abnormal transport properties are considered to be a sign of a martensitic transition in the TP2 temperature region. Besides, all the samples clearly reveal the unusual low temperature resistivity minimum, presumably due to the combined effect of weak localization, electron–electron and electron–phonon scattering. The present results are discussed and possible explanations were given based on the related theory and previous reported results.

Complex Analysis of Electrical Resistivity Dynamics of Co&lt;sub&gt;82&lt;/sub&gt;Fe&lt;sub&gt;4&lt;/sub&gt;Cr&lt;sub&gt;3&lt;/sub&gt;Si&lt;sub&gt;8&lt;/sub&gt;B&lt;sub&gt;3&lt;/sub&gt; Amorphous Alloy under Heat Treatment

In this paper the detailed analysis of thermal behavior of electrical resistivity of Co82Fe4Cr3Si8B3 amorphous alloy is made. It has been shown that within temperature range 230С &lt;T&lt; 5600С the structure of the alloy keeps its amorphous character and only a slight changes occurred. A high temperature (above room temperature) resistivity minimum was found at 160°C. This feature was related with Curie temperature of the alloy. It has been shown that change of electrical resistivity behavior at 350°C can be explained by reaching the Debye temperature of the alloy.

Crossover effect of inter-granular transport and quantum correction in Co-doping La2/3Ca1/3MnO3 manganites

The dependence of electrical transport on temperature and magnetic field is studied systemically in La2/3Ca1/3Mn1−xCoxO3 (x=0–0.15) systems between 2.5 and 300K in magnetic field ranging from 0 to 6T. The substitution of Co at Mn site results in weakening the ferromagnetism, a deterioration of the metallic conductivity. The PM–FM transition is broadened with increasing Co doping content x, and the magnetic spontaneous state has changed into a cluster glass state for the sample of x=0.15. The resistivity minima are clearly observed at low temperature (T<50K) for all the samples. An unusual modulation effect under magnetic field for low temperature resistivity minimum of the Co-doping samples is observed. The abnormal behavior of Co-doped samples is that the resistivity minimum temperature (Tmin) shifts to higher temperatures with the increase in magnetic field. It is distinctly different from undoped and low doped samples where Tmin shifts to lower temperature under higher magnetic fields. In other words, the resistivity upturn of Co-doped samples is enhanced by magnetic field instead of the general field suppression effect. The observed resistivity minimum at low temperatures is partly due to the coexistence of electron–electron interaction enhanced by an intrinsic magnetic inhomogeneity and spin polarization tunneling through grain boundaries. The electron–electron scattering due to the Coulomb interaction is the intrinsic mechanism for the low temperature resistivity upturn. Electrical resistivity behavior of the compounds as function of temperature at paramagnetic state could be explained on the basis of variable-range hopping model.

Low temperature resistivity minimum and its correlation with magnetoresistance in La 0.67Ba 0.33MnO 3 nanomanganites

A systematic investigation of structural, magnetic and electrical properties of nanocrystalline La 0.67Ba 0.33MnO 3 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.

Resistivity Minimum Behavior and Weak Magnetic Disorder Characteristics in La2/3Ca1/3MnO3 Manganites

The correlation of low temperature resistivity minimum with magnetic properties was studied by a tuned action in applied magnetic fields for the optimal doping La2/3Ca1/3MnO3 manganite. It is proved that the low temperature minimum results from the existence of intrinsic spin disorder with a weak magnetic disorder characteristic caused from antiferromagnetism background and ferromagnetic ground state. The best fittings were made for the high field, accompanied by disappearing of Kondo term; the electronic resistivity follows only T1/2 dependence with a characteristic of enhanced e-e interactions and carrier localization. This e-e interaction at low and high fields would be a general characteristic and it reflects the strong correlated interaction between electrons in mixed-valent manganites.

Electrical properties of Ag–La 0.7Ca 0.3MnO 3

The temperature dependence of the electrical resistivity in (1 − x) La 0.7Ca 0.3MnO 3 + xAg composites has been investigated between 5 and 300 K for H = 0 and 3 T. Ag addition has increased the conductivity of this system. Curie temperature ( T C) is almost independent of Ag content and is ~ 260 K for all the samples, while the metal–insulator transition temperature ( T MI) increases with increasing content of Ag. The ρ–T of all samples fit well with the phenomenological percolation approach, which is based on the phase segregation of ferromagnetic metallic clusters and paramagnetic insulating regions. In addition, all the samples clearly reveal the unusual low temperature resistivity minimum. Analysis of our results in terms of the model based on charge carrier tunneling between the anti-ferromagnetically coupled grains shows excellent agreement with the experiment data for both H = 0 and 3 T.

Phase stability and properties of the hole doped perovskite cobaltites (La 1− xR x) 0.7Ba 0.3CoO 3− δ (0.0≤ x≤1.0; R=Pr, Nd)

The structural, magnetic and electrical properties of the hole doped cobaltites, with compositions (La 1− x R x ) 0.7Ba 0.3CoO 3 (0.0≤ x≤1.0; R=Pr, Nd), have been studied. Substitutions of Pr and Nd for La destabilize the stoichiometric perovskite structure at the benefit of the ordered oxygen deficient perovskite ‘112’-type structure, due to decrease in size of the rare earth ion. Our studies show that for our synthesis condition, the samples of nominal compositions, R 1− y Ba y CoO 3 (R=Pr, Nd), can form with the perovskite structure only for y<0.3. In the single-phase regions, the thermo-magnetic irreversibility and coercive field increase with the substitution of Pr and Nd for La. The low temperature resistivity minimum and negative magneto-resistance in the insulating regions of these polycrystalline compounds have been ascribed to grain boundary effects.

Electrical resistivity and the Néel point of Mn 100 − xCr x thin films

Electrical resistivity measurements have been carried out on thermal evaporated Mn 100 − x Cr x ( x=0.5,1,2,) thin films between 300 and 1.4 K using the van der Pauw four probe technique. A resemblance of the resistivity-temperature behaviour typical of the bulk α-Mn-Rich, specimen is obtained with the 0.5 at.% Cr in Mn. The Néel point of this specimen is shifted to 83±1 K from the known value of 90±1 K for α-Mn. The Néel point is shifted further to lower values as the concentration of Cr in Mn increases. The low temperature resistivity minimum may be interpreted as due to the presence of Cr impurities in the Mn film giving rise to a distortion of the magnetic moment of the manganese atoms and thus leading to spin fluctuation scattering of the conduction electrons.

Effects of rare-earth substitutions for U in URu 2Si 2

The effects of rare earth substitutions for U in URu 2Si 2 are summarised. While La, Ce, Pr, Nd, and Lu substitutions of around 5% depress the resistivity anomaly at 17.5 K, those of Sc, Y, Th and heavy rare earths leave its temperature little changed but its size greatly attenuated. Elements of this latter group, however, also induce a lower temperature resistivity minimum which is ascribed to the production of better defined moments on some neighbouring U atoms.

Correlation between the residual resistivity and the temperature resistance minimum in amorphous alloys

A simple formula for the correlation between the residual resistivity and the temperature resistivity minimum in amorphous transition metal-metalloid alloys is derived by means of the Ziman potential scattering theory and the Kondo spin-flip scattering theory.

On the high temperature electrical resistivity behaviour of Cu 55-Ni 45 alloy

Resistivity measurements supplemented with electron microscopy investigation in a Cu 55-Ni 45 alloy are reported, in the temperature range 273–700 K. An anomalous high temperature resistivity minimum is observed at 673 K whereas at the same temperature diffuse intensity maxima appear. It is suggested that the resistivity minimum could be attributed to the effect of short range order cluster formation.

Low temperature resistivity minimum in MnAs 1− xP x compounds

The conductivity and the magnetic moment of MnAs 1− x P x single crystals have been measured in the temperature range from 5 to 300 K and for compositions between x = 0.03 and x = 0.12. Comparison of the temperature dependence of the magnetic moment with that of the electrical resistivity yields a connection between a low temperature resistivity minimum which resembles the Kondo-Nagaoka type anomaly and a sharp decrease of the magnetic moment. In this temperature range the magneto-resistance is relatively large (∽ 5%) and negative. A small temperature hysteresis and a slow response to magnetic fields is observed. The occupation of quasi-bound states at the cation sites by the conduction electrons would explain qualitatively the observations.

Microstructure of amorphous and crystalline electrodeposited Ni-P and Co-P alloys

A new model for the microstructure of electrodeposited Ni-P and Co-P alloys is presented based upon the concept of grain boundary segregation. The model correctly explains the compositional dependence of grain size as well as other experimental data. The model also predicts an anomalous low temperature heat capacity and a low temperature resistivity minimum. Both these predictions are confirmed experimentally.