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This work studies the influence of microstructures and crystalline defects on the superconductivity of MgB[sub 2], with the objective to improve its flux pinning. A MgB[sub 2] sample pellet that was hot isostatic pressed (HIPed) was found to have significantly increased critical current density (J[sub c]) at higher fields than its un-HIPed counterpart. The HIPed sample had a J[sub c] of 10 000 A/cm² in 50 000 Oe (5 T) at 5 K. This was 20 times higher than that of the un-HIPed sample, and the same as the best J[sub c] reported by other research groups. Microstructures observed in scanning and transmission electron microscopy indicate that the HIP process eliminated porosity present in the MgB[sub 2] pellet resulting in an improved intergrain connectivity. Such improvement in intergrain connectivity was believed to prevent the steep J[sub c] drop with magnetic field H that occurred in the un-HIPed MgB[sub 2] pellet at H >45 000 Oe(4.5 T) and T = 5 K. The HIP process was also found to disperse the MgO that existed at the grain boundaries of the un-HIPed MgB[sub 2] pellet and to generate more dislocations in the pellets. These dispersed MgO particles and dislocations improved flux pinning also at H < 45 000 Oe. The HIPing process was also found to lower the resistivity at room temperature. [ABSTRACT FROM AUTHOR]

The crystalline electric field (CEF) energy level scheme of the heavy fermion superconductor CeCoIn5 has been determined by means of inelastic neutron scattering (INS). Peaks observed in the INS spectra at ∼8 and ∼27 meV with incident neutron energies between Ei=30 and 60 meV and at a temperature T=10 K correspond to transitions from the ground state to the two excited states, respectively. The wave vector and temperature dependence of these peaks are consistent with CEF excitations. Fits of the data to a CEF model yield the CEF parameters B20=-0.80 meV, B40=0.059 meV, and |B44|=0.137 meV corresponding to an energy level scheme: Γ7(1)(0)[=0.487|±5/2>-0.873|∓3/2>], Γ7(2)(8.6 meV,100 K), and Γ6(24.4 meV,283 K). © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The results of 115In nuclear quadrupole resonance (NQR) measurements on Ce1-xYxRhIn5 and Ce1-xLaxRhIn5 are reported. The observed NQR frequency at an In(1) site varies linearly with lattice parameter and dopant concentration for Y- and La-substituted systems. For the samples of LaMIn5 (M=Co,Rh,Ir) and YRhIn5, T1-1’s are proportional to the temperature, which means the system is in the Fermi liquid state in a wide temperature range. On the other hand, in Ce0.1La0.9RhIn5 and Ce0.5Y0.5RhIn5, T1-1’s have power-law temperature dependences (close to T1/4), which are expected to be from non-Fermi-liquid behavior near a quantum critical point. For Ce0.5La0.5RhIn5 and Ce0.25La0.75RhIn5, T1-1’s stay temperature independent below 4.2 K and the observed linewidths of 115In become broader with decreasing temperature. This behavior may be associated with a short-range magnetic order of Ce expected from the macroscopic measurements. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Results of studies of the susceptibility, magnetic specific heat, and electron paramagnetic resonance spectrum of the geometrically frustrated antiferromagnetic ZnCr[sub 2]O[sub 4] are presented. The temperature dependence of the susceptibility and the specific heat are in good agreement with the predictions of the quantum tetrahedral mean field model for exchange-coupled spin-3/2 ions on a pyrochlore lattice. The origin of the anomalous behavior of the resonance intensity below 90 K is discussed. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

High temperature electron spin resonance (ESR) and magnetic susceptibility (χ) are analyzed for manganites related with colossal magnetoresistance (CMR). The properties of compounds with different crystalline structures: three-dimensional (3D) perovskites, pyrochlore, and La[sub 1.2]Sr[sub 1.8]Mn[sub 2]O[sub 7], a two-dimensional layer, are compared. In the paramagnetic regime, and outside the critical regions associated with phase transitions, the temperature dependence of the ESR linewidth presents a universal behavior dominated by the variations of χ(T), ΔH[sub pp](T)=[C/Tχ(T)]ΔH[sub pp](∞). The high temperature limit of the linewidth, ΔH[sub pp](∞), is related to the parameters of the Hamiltonian describing the interactions of the spin system. The role played by magnetic anisotropy, isotropic superexchange, and double exchange is revealed and discussed in the analysis of the experimental data. In CMR and non-CMR pyrochlores, ΔH[sub pp](∞)∝ω[sub p][sup 2]/J where J is proportional to the Curie–Weiss temperature, including the hybridization mechanism producing CMR. Instead, ΔH[sub pp](∞) of CMR perovskites seems not to be affected by the double-exchange interaction. In contrast with the 3D perovskites, the ESR linewidth and resonance field of La[sub 1.2]Sr[sub 1.8]Mn[sub 2]O[sub 7], a bilayer compound, although isotropic at high temperatures, becomes anisotropic for T[sub c]=125 K

A correction to the article "Mean field renormalization group: A theoretical approach to the Fe1-qAlq in the bcc lattice" that was published in the June 15, 2012 online issue is presented.

In this work, the site diluted Heisenberg model is applied to study the magnetic properties of the bcc disordered phase of FeAl alloys by employing mean field renormalization group theory. We suggest a new approach to exchange interaction between nearest neighbors of Fe that depends on de powers of the Al (q) instead of the linear dependence proposed in other papers. Excellent agreement with the experimental data in the T - q plane have been obtained, in particular, in the region with anomalous behavior of the alloy concerned. [ABSTRACT FROM AUTHOR]

The crystalline electric field (CEF) energy level scheme of the heavy fermion superconductor CeCoIn5 has been determined by means of inelastic neutron scattering (INS). Peaks observed in the INS spectra at ∼8 and ∼27 meV with incident neutron energies between Ei=30 and 60 meV and at a temperature T=10 K correspond to transitions from the ground state to the two excited states, respectively. The wave vector and temperature dependence of these peaks are consistent with CEF excitations. Fits of the data to a CEF model yield the CEF parameters B20=-0.80 meV, B40=0.059 meV, and |B44|=0.137 meV corresponding to an energy level scheme: Γ7(1)(0)[=0.487|±5/2>-0.873|∓3/2>], Γ7(2)(8.6 meV,100 K), and Γ6(24.4 meV,283 K). © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]