Search

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.

A comprehensive study of superconducting and normal state properties of Nb2Pd(S0.9Te0.1)5 system which consists of solid chunks embedded with mesh of fibers has been presented here. Below the superconducting transition temperature, in different iso-magnetic fields, the motion of vortices in mixed state has been analyzed using thermally activated flux flow (TAFF) model and the obtained thermal activation energy (TAE) follows Kramer’s scaling which suggests the dominance of mechanism similar to grain boundary pinning in these fibers. Bulk nature of superconductivity is clearly seen in specific heat data, however with a jump of ∼0.97, less than the BCS estimate, places these fibers in weak coupling strength limit. Low temperature electronic heat capacity down to 2 ​K point towards a fully gapped s-wave superconductivity in these fibers. Moreover, normal state study using thermoelectric power data suggests a hole dominated transport in this system.

We have reported in this work the study of correlation between electrical transport and magnetic properties of La 0.5 Ca 0.5 Mn 0.98 Bi 0.02 O 3 polycrystalline sample prepared by solid state method. Structural analysis reveals that presently studied compound crystallizes in the orthorhombic structure with Pnma space group. Temperature dependence of magnetization indicates that our studied compound undergoes a paramagnetic–ferromagnetic transition at Curie temperature T C =237 K. Magnetotransport analysis was successfully carried out using percolation model in the temperature range 40–300 K for magnetic field values up to 14 T. Strong correlation between electrical and magnetic properties was observed along with the absence of charge ordering inside the structure of our sample.

We have reported in this work the effect of the partial substitution of lanthanum by samarium on the structural, electrical and magnetic properties of La 0.5 Ca 0.5 MnO 3 . The magnetic study indicated that substitution promotes charge ordering and weakens ferromagnetism. Below T C =123 K, the compound La 0.4 Sm 0.1 Ca 0.5 MnO 3 is a mixture of ferromagnetic and charge ordered antiferromagnetic domains. Between T C and T CO =215 K, the structure is paramagnetic with the presence of antiferromagnetic domains. The fractions of the coexisting magnetic phases are highly dependent on the applied magnetic field value. Resistivity measurements reveal the presence of an insulating-metal transition at T ρ =123 K. The equality between T C and T ρ indicates the presence of a correlation between magnetization and resistivity. For only 1 T applied field, we have reported a colossal value of magnetoresistance reaching 73% around T C . The origin of this high value is attributed to phase separation phenomenon.

The thermoelectric power (TEP), resistivity, and heat capacity of the polycrystalline Ce(Ni1−xCux)2Al3 system, for x = 0.0–0.4, are reported. A clear enhancement of TEP at low temperatures is seen upon substitution of Cu and is expected to be useful for low-temperature thermoelectric applications. To understand such an enhanced TEP we have employed a two-band model based on the Ce-4f and conduction bands proposed by Gottwick et al. A clear evolution of a 4f band moving toward the Fermi level that is becoming sharpened is seen and is predicted to be close to resonance. The fit parameters of the TEP (S) are physically reasonable. The resistivity data shows an evolution from a simple compensated metal to a paramagnetic one via the Kondo route. This is in line with TEP parameters. In addition, a clear enhancement seen in the electronic part of the heat capacity upon Cu substitution and the evolution of magnetoresistance behavior corroborates the results. Possible bipolar effects are also taken into consideration along with an electron–phonon interaction term to explain the almost temperature-independent part of the resistivity, still yielding a considerable component of disorder.

The superconducting transition temperature of niobium silicon oxynitride (Nb0.87Si0.09□0.04)(N0.87O0.13) exhibits a gradual reduction from 16.8 K to around 11 K under an increasing applied magnetic field of up to 14 T. This relatively small Tc reduction under an applied magnetic field suggests a robustness of its superconducting behavior in comparison to that in the parent niobium oxynitride. It was similar to the flux pinning effect observed in the large magnetic hysteresis of the niobium-silicon oxynitrides in our previous study. Both Si K-edge XANES and 29Si MAS-NMR indicated that the local structure of pinning centers around the silicon atoms close to cationic vacancies was similar to that of Si in amorphous SiO2 in the rock-salt structure of niobium oxynitride.

Unusual magnetoresistance observed in weak itinerant ferromagnetic metal Fe0.9Co0.1Si is addressed. We invoke localization effects significantly contributing to the positive magnetoresistance apart from quantum interference effects (QIE), a new mechanism for magnetoresistance at low temperatures. QIE are dominant only at very low temperatures while localization effects are progressive out of the sub-Kelvin domain. Dominance of localization effects in Kelvin range with increasing applied magnetic field is demonstrated. An unconventional effect of magnetic field on resistivity, favors a least dominant role of ferromagnetic correlations. The H–T phase diagram explore the regions of H3/2 (paramagnetic region) and QIE (Δσ ∝ H1/2) and its extension into the paramagnetic region. A new region of linear field dependence of MC (Δσ ∝ H) is also found and reported. Qualitative analysis of thermopower and its correspondence with electrical resistivity strengthens the concept that the same electrons are responsible for both electrical and magnetic properties. It is also reported that the onset of magnetic and QIE effects is well above TC.

Niobium compounds continue to be an interesting family of superconductors, with the recent addition of oxynitrides to it, which can be categorized as low-Tc superconductors (LTS) because they exhibit superconductivity below Tc∼17 K. In this paper, we report the superconducting properties of three members of the family of niobium oxynitrides, viz. (Nb0.89Al0.11)(N0.84O0.16), (Nb0.95Mg0.05)(N0.92O0.08) and (Nb0.87Si0.09□0.04)(N0.87O0.13). Low temperature dc and ac magnetization measurements have been performed. In addition, heat capacity has been recorded at low temperature under applied magnetic fields. A detailed analysis of the data is presented.

The resistivity and heat capacity of CeAl, a well-known Kondo system, is probed under high magnetic fields of up to 14 T. The system is known to undergo a first-order structural phase transition from hexagonal to monoclinic phase at 110 K. The current study has revealed that this structural transition is a robust one under high magnetic fields. However, clear dispersion in resistivity and heat capacity are seen in the presence of high magnetic fields below 30 K, whose analysis suggest its nearness to quantum critical point (QCP). Systematic vanishing of Kondo ordering ( behaviour) and the appearance of non-Fermi liquid behaviour (+ behaviour) around 6–9 T region at low temperatures suggest that the system settles for a QCP. In line with the resistivity, the heat capacity also revealed signatures reminiscent of a non-Fermi liquid. The first-time confirmation about the existence of a QCP in stoichiometric CeAl makes this already-known compound more interesting because it could lead to the discovery of possible new ground states.

Mn11Ge8 undergoes long range ferromagnetic ordering at 274 K followed by non-collinear antiferromagnetic structure below 150 K. Our investigations indicate the existence of large positive magnetoresistance which changes sign depending upon the applied field and temperature. In the temperature variation of resistivity and heat capacity, the sample shows very large coefficients of quadratic and linear terms, respectively. This indicates the existence of giant spin fluctuation despite the fact that the sample is in a magnetically ordered state. The Mn-moments possibly have both localized and itinerant character and the anomaly appears to be associated with the local moment spin fluctuations mediated via itinerant electrons. The large positive magnetoresistance is believed to be originated from the possible development of short range antiferromagnetic clusters on application of magnetic field.

The theoretically proposed pseudogap semimetal CoSi has been investigated by detailed experimental studies of magnetotransport, calorimetric and thermopower measurements. The two parallel resistor model is applied to understand its semimetal nature. The obtained gap is around 13 meV. The conduction process is explained by the single relaxation method by implementing Kohler's rule, , . The excess heat capacity is a consequence of thermally activated behaviour across the gap and the calculated is about . At K, the metallic behaviour without the gap, vanishing of excess heat capacity, reasonable metallic value of and linear diffusion thermopower, signifies the closure of pseudogap. The correlation amongst the T-dependent features of resistivity, excess heat capacity and thermoelectric power reveals the hidden metal-to-insulator transition in CoSi. The high magnetoresistance at low temperatures is reported to arise due to Lorentz force and its applications as a low temperature magnetic field sensor is also discussed.