G. Narsinga Rao

Evolution of size, morphology, and magnetic properties of CuO nanoparticles by thermal annealing

Cupric oxide (CuO) nanoparticles with different morphologies were synthesized by thermal annealing of the copper hydroxide at various temperatures. Significant changes in both the particle size and the morphology with the annealing temperature (TA) were observed. The average particle size (d) increases from 13 to 33 nm and the morphology varies from ellipsoidal to rodlike as TA increases from 150 to 550 °C. The formation of these morphologies is explained in terms of the variation in the interplanar H-bonds breaking rate with different temperatures. The magnetic measurements reveal the presence of weak ferromagnetic interaction and the blocking behavior in these nanoparticles. The magnetic field dependence of the superparamagnetic blocking temperature (TB) follows the Brown equation. In addition, the linear variation in zero field cooled susceptibility with particle size is consistent with the predictions of Neel model for the uncompensated spins. These surface spins are responsible for the observed anoma...

Double peak behavior of resistivity curves in Cd doped LaMnO3 perovskite systems

Abstract The effect of Cd doping on transport, magnetotransport, and magnetic properties has been investigated in the perovskite La1−xCdxMnO3 (0⩽x⩽0.5) systems. The ρ(T) curves exhibit a sharp metal insulator transition (Tp1), which is close to paramagnetic to ferromagnetic transition (Tc) obtained from M−T curves for all samples. In addition, ρ(T) curves for Cd doped samples exhibit another broad transition (TP2) below Tp1. This transition becomes more prominent and the transition temperature (Tp2) shifts to lower temperature with increasing Cd content. Such double peak behavior in the ρ(T) curve is attributed to the phase separation between the ferromagnetic metallic phases and the ferromagnetic insulating phases induced by the electronic inhomogeneity in the samples.

Influence of Mn substitution on microstructure and magnetic properties of Cu1−xMnxO nanoparticles

Mn-doped CuO nanoparticles were synthesized using a coprecipitation method. Powder x-ray analysis reveals that all the samples crystallize into a monoclinic-type structure. Significant changes occur in both the microstructure and particle size with calcination temperature TA. The average particle size d increases from 11to85nm as the TA increases from 250to850°C. For particles of size d⩽22nm, energy dispersive spectroscopy indicates the existence of a crystalline Cu1−xMnxO core surrounded by an amorphous CuO shell. M(T) curves reveal a spin-glass behavior for the 11 and 22nm particles and a ferromagnetic behavior for particles of size d⩾35nm. The observed ferromagnetic behavior is attributed to the coexistence of Mn2+ and Mn3+ ions.

Crystal growth of Dirac semimetal ZrSiS with high magnetoresistance and mobility

High quality single crystal ZrSiS as a theoretically predicted Dirac semimetal has been grown successfully using a vapor phase transport method. The single crystals of tetragonal structure are easy to cleave into perfect square-shaped pieces due to the van der Waals bonding between the sulfur atoms of the quintuple layers. Physical property measurement results including resistivity, Hall coefficient (RH), and specific heat are reported. The transport and thermodynamic properties suggest a Fermi liquid behavior with two Fermi pockets at low temperatures. At T = 3 K and magnetic field of Hǁc up to 9 Tesla, large magneto-resistance up to 8500% and 7200% for Iǁ(100) and Iǁ(110) were found. Shubnikov de Haas (SdH) oscillations were identified from the resistivity data, revealing the existence of two Fermi pockets at the Fermi level via the fast Fourier transform (FFT) analysis. The Hall coefficient (RH) showed hole-dominated carriers with a high mobility of 3.05 × 104 cm2 V−1 s−1 at 3 K. ZrSiS has been confirmed to be a Dirac semimetal by the Dirac cone mapping near the X-point via angle resolved photoemission spectroscopy (ARPES) with a Dirac nodal line near the Fermi level identified using scanning tunneling spectroscopy (STS).

Magnetic Orderings in Li2Cu(WO4)2 with Tungstate-Bridged Quasi-1D Spin-1/2 Chains.

By both experimental measurements and theoretical calculations, we investigated the magnetic and electronic properties of Li2Cu(WO4)2 as a tungstate-bridged quasi-one-dimensional (1D) copper spin-(1/2) chain system. Interestingly, magnetic susceptibility χ(T) and specific heat measurements show that the system undergoes a three-dimensional antiferromagnetic (AF)-like ordering at TN ≈ 3.7 K, below a broad χ(T) maximum at ∼8.9 K indicating a low-dimensional short-range AF spin correlation. Bonner-Fisher model fitting of χ(T) leads to an AF intrachain exchange constant of J/kB = 15.8 ± 0.1 K, and mean-field theory estimation gives an interchain coupling constant of J⊥/kB = 1.6 K, which supports the quasi-1D nature of this spin system. Theoretical evaluation of exchange coupling constants within the generalized gradient approximation (GGA) plus on-site Coulomb interaction (U) shows that the dominant AF exchange interaction is of ∼13.9 K along the a-axis with weak interchain coupling, in agreement with the experimental result of a quasi-1D spin-(1/2) chain system. The GGA+U calculations also predict that Li2Cu(WO4)2 is a charge transfer-type AF semiconductor with a direct band gap of 1.5 eV.

Tellurium-bridged two-leg spin ladder inBa2CuTeO6

We present single-crystal growth and magnetic property studies of tellurium-bridged copper spin-1/2 system Ba

Antiferromagnetism of Ni 2 NbBO 6 with S = 1 dimer quasi-one-dimensional armchair chains

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Successive spin orderings of tungstate-bridged Li2Ni(WO4)2 of spin 1.

CuTeO

Dielectric studies of Fe Doped SmCrO3 Perovskites

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MAGNETIC RELAXATION, LOWER CRITICAL FIELD AND IRREVERSIBILITY LINE OF W DOPED (Bi, Pb)-2223 SUPERCONDUCTOR

. The spin-exchange interaction among copper spins via Cu-O-Te-O-Cu super-superexchange route leads to a novel two-leg spin ladder system. Spin susceptibility