Chiranjib Mitra

Enhanced room-temperature magnetoresistance in La0.7Sr0.3MnO3-glass composites

In this letter, we report the improved magnetotransport properties of La0.7Sr0.3MnO3-borosilicate glass composite with different weight percents of glass. All the composites showed ferromagnetic nature at room temperature. The microstructure of these composites was seen using a scanning electron microscope. The microstructure was reconfirmed using spot energy dispersive x-ray analysis. We observe an enhancement of the low-field magnetoresistance (<200 Oe) at room temperature for the optimal composition of 25 wt % of glass. It is argued that glass layer separating the grain boundaries may be acting as barrier for spin-polarized tunneling, thereby enhancing the low-field magnetoresistance.

p–n diode with hole- and electron-doped lanthanum manganites

The hole-doped (p-) manganite La0.7Ca0.3MnO3 and the electron-doped (n-) manganite La0.7Ce0.3MnO3 undergo an insulator-to-metal transition at around 250 K, above which both behave as a polaronic semiconductor. We have fabricated an epitaxial trilayer (La0.7Ca0.3MnO3/SrTiO3/La0.7Ce0.3MnO3), where SrTiO3 is an insulator. At room temperature, i.e., in the semiconducting regime, it exhibits asymmetric current–voltage (I–V) characteristics akin to a p–n diode. The observed asymmetry in the I–V characteristics disappears at low temperatures where both the manganite layers are metallic. These results indicate that using the polaronic semiconducting regime of doped manganites, a p–n diode can be constructed.

Growth of epitaxial and polycrystalline thin films of the electron doped system La1−xCexMnO3 through pulsed laser deposition

The polycrystalline La1−xCexMnO3 manganites do not exist in single phase in bulk under the preparation conditions so far employed, but their polycrystalline and epitaxial films deposited by the pulsed laser deposition (PLD) technique form readily in single phase. The cerium oxide (CeO2) remains partially unreacted when the bulk sample is prepared through the solid state reaction route. The resistivity of the bulk La0.7Ce0.3MnO3 sample shows a broad metal insulator transition (MIT) clearly resolved into two peaks, suggesting the presence of a second (impurity) phase, which is identified as unreacted CeO2 by the intensity analysis of the x-ray diffraction (XRD) data. However, when prepared as thin films by PLD, La0.7Ce0.3MnO3 forms in single phase, as corroborated by the uniqueness and sharpness of the MIT peak and also by the XRD patterns of the polycrystalline films. We also performed a detailed study of the epitaxial films by a high-resolution XRD system with a four-circle goniometer and did not find any...

Molecular Thin Films: A New Type of Magnetic Switch

The magnetic coupling of flexible metal phthalocyanine (MPc) thin films can be modified depending on the polymorphic form adopted by the crystals. A simple annealing procedure can switch the couplings from antiferromagnetic to ferromagnetic (MnPc) or paramagnetic (CuPc), opening up avenues for spintronic applications. Density functional and perturbation theories rationalize these trends and attribute the coupling mechanism to indirect exchange.

Evolution of transport and magnetic properties with dysprosium doping in La0.7−xDyxSr0.3MnO3 (x=0–0.4)

Abstract We report the magnetic and transport properties in the series La 0.7− x Dy x Sr 0.3 MnO 3 (0.0⩽ x ⩽0.4). Susceptibility and resistivity studies show that La 0.7− x Dy x Sr 0.3 MnO 3 for x x , ultimately leading to a spin-glass-like state for x >0.3 compounds. The sample with x =0.4 shows a dramatic increase in resistivity near the spin-glass ordering temperature T SG .

The effect of holmium doping on the magnetic and transport properties of

We have studied the evolution of the transport and magnetic properties with holmium doping for . We observe a systematic decrease in the ferromagnetic transition temperature , the metal - insulator transition temperature and the rhombohedral cell volume with increasing holmium concentration. For the concentration with x = 0.4, we observe a metallic spin-glass phase with the spin-glass freezing temperature , and a large magnetoresistance ratio at low temperature, which indicates that a proportion of the spins are in a frustrated state. The high-field magnetization of the holmium-doped samples is much less than the magnetization that would be expected if the were in a ferromagnetic state, showing that there is substantial canting in the manganese lattice. We believe that the ferromagnetic component in the spin-glass phase for x = 0.4 crosses the percolation threshold, giving rise to metallicity in the sample.

Teleportation in the presence of common bath decoherence at the transmitting station

We investigate the effect of common bath decoherence on the qubits of Alice in the usual teleportation protocol. The system bath interaction is studied under the central spin model, where the qubits are coupled to the bath spins through isotropic Heisenberg interaction. We have given a more generalized representation of the protocol in terms of density matrices and calculated the average fidelity of the teleported state for different Bell state measurements performed by Alice. The common bath interaction differentiates the outcome of various Bell state measurements made by Alice. There will be a high fidelity teleportation for a singlet measurement made by Alice when both the qubits of Alice interact either ferromagnetically or antiferromagnetically with bath. In contrast if one of Alices qubits interacts ferromagnetically and the other antiferromagnetically then measurement of Bell states belonging to the triplet sector will give better fidelity. We have also evaluated the average fidelity when Alice prefers nonmaximally entangled states as her basis for measurement.

Magnetotransport properties of a room temperature rectifying tunnel junction made of electron and hole doped manganites

The hole-doped (p) manganite La0.7Ca0.3MnO3 and the electron-doped (n) manganite La0.7Ce0.3MnO3 undergo an insulator-to-metal transition at around 250 K, above which both behave as a polaronic semiconductor. We have fabricated an epitaxial trilayer (La0.7Ca0.3MnO3/SrTiO3/La0.7Ce0.3MnO3), where SrTiO3 is an insulator. At room temperature, i.e., in the semiconducting regime, it exhibits asymmetric current–voltage (I–V) characteristics akin to a p–n diode. The observed asymmetry in the I–V characteristics disappear at low temperatures where both the manganite layers are metallic. The I–V curves exhibit an intriguing temperature dependence in the presence of magnetic field. At room temperature, i.e., above the ordering temperature, we have a negative magnetoresistance (MR) and at low temperature we have a positive MR, indicative of a minority spin carrier band in La0.7Ce0.3MnO3. A possible mechanism for the observed effects are discussed.

Experimental detection of quantum information sharing and its quantification in quantum spin systems

We study the macroscopic entanglement properties of a low- dimensional quantum spin system by investigating its magnetic properties at low temperatures and high magnetic fields. The spin system chosen for this is copper nitrate (Cu(NO3)2 ◊2.5H2O), which is a spin chain that exhibits dimerization. The temperature and magnetic field dependence of entanglement from the susceptibility and magnetization data are given, by comparing the experimental results with the theoretical estimates. Extraction of entanglement has been made possible through the macroscopic witness operator, magnetic susceptibility. An explicit comparison of the experimental extraction of entanglement with theoretical estimates is provided. It was found that theory and experiments match over a wide range of temperatures and fields. The spin system studied exhibits quantum phase transition (QPT) at low temperatures when the magnetic field is swept through a critical value. We show explicitly for the first time, using tools used in quantum information processing, that QPT can be captured experimentally using quantum complementary observables, which clearly delineate entangled states from separable ones across the QPT.

The nature of magnetism in CeScSi and CeScGe

Conflicting reports on the nature of the magnetic transition in CeScSi and CeScGe have appeared in the literature. We have readdressed this problem in this report by working on well characterized polycrystalline samples. Our data prove conclusively that the two compounds order antiferromagnetically at TN≈26 and 46 K, respectively. An analysis of the x-ray diffraction intensity profile in the polycrystalline samples and a structural refinement of CeScSi by single-crystal work showed that these are crystallographically well ordered intermetallics. It is important to anneal the compounds at the proper temperature to remove parasitic impurity phases which are present in the as-cast materials and are the likely cause of the conflicting reports on these two compounds.