Nuclear magnetic resonance study of the magnetic-field-induced ordered phase in the NiCl2-4SC(NH2)2 compound

Nuclear magnetic resonance (NMR) study of the high magnetic field (H) part of the Bose-Einstein condensed (BEC) phase of the quasi-onedimensional (quasi-1D) antiferromagnetic quantum spin-chain compound NiCl2-4SC(NH2)2 (DTN) was performed. We precisely determined the phase boundary, Tc(H), down to 40 mK; the critical boson density, n_c(Tc); and the absolute value of the BEC order parameter S_perp at very low temperature (T = 0.12 K). All results are accurately reproduced by numerical quantum Monte Carlo simulations of a realistic three-dimensional (3D) model Hamiltonian. Approximate analytical predictions based on the 1D Tomonaga-Luttinger liquid description are found to be precise for Tc(H), but less so for S_perp(H), which is more sensitive to the strength of 3D couplings, in particular close to the critical field. A mean-field treatment, based on the Hartree-Fock-Popov description, is found to be valid only up to n_c = 4% (T < 0.3 K), while for higher n_c boson interactions appear to modify the density of states.Comment: Manuscript (6 pages, 3 figures) and the corresponding Supplemental material (5 pages, 6 figures), altogether 11 pages and 9 figure

Magnetic Impurities in the Pnictide Superconductor Ba1−x_{1-x}Kx_{x}Fe2_{2}As2_{2}

NMR measurements have been performed on single crystals of Ba$_{1-x}$K$_{x}$Fe$_2$As$_2$ (x = 0, 0.45) and CaFe$_2$As$_2$ grown from Sn flux. The Ba-based pnictide crystals contain significant amounts of Sn in their structure, $\sim 1$%, giving rise to magnetic impurity effects evident in the NMR spectrum and in the magnetization. Our experiments show that the large impurity magnetization is broadly distributed on a microscopic scale, generating substantial magnetic field gradients. There is a concomitant 20% reduction in the transition temperature which is most likely due to magnetic electron scattering. We suggest that the relative robustness of superconductivity ($x=0.45$) in the presence of severe magnetic inhomogeneity might be accounted for by strong spatial correlations between impurities on the coherence length scale.Comment: 14 pages, 6 figures (submitted to New Journal of Physics

Rare-Earth Ion-Assisted Nuclear Spin-Lattice Relaxation in Nd^3^+-Doped Binary Sodium Borate Glasses: ^1^1B NMR Study

Rare-Earth (RE) doped glasses are promising candidates for laser and other opto-electronic applications. The optical properties of the RE doped glasses depend on the symmetry and environment of the RE ion in the host glass and hence its structure. We have studied Nd^3^+ doped $3ONa_2O-(70-x)B_2O_3-xNd_2O_3$ glasses with various Nd^3^+ concentrations sx=0, 0.1, 0.5,1 mol%d using ^1^1B NMR. In this paper we have presented a method of estimating the crystal field splitting of the RE ion using 11B Nuclear Spin-Lattice Relaxation (NSLR) time measurements in these systems as a function of temperature in the range 100–4.2 K. Details of the magnetization recovery fit, theory of ^1^1B relaxation time are discussed in terms of possible relaxation mechanisms in the presence of a RE ion. We found that the relaxation can be explained using a two-level system (TLS) model for x=0 and the Orbach process for other samples. The magnetization recovery is observed to fit better to a single exponential model in all the samples as evident from the statistical analysis of the fit. The crystal field splitting sDd estimated from our studies are found to be around 100 cm^−^1, in agreement with other Nd^3^+-doped systems reported in the literature

Experimental and Theoretical Investigation of Magnetoresistance From Linear Regime to Saturation in 14-nm FD-SOI MOS Devices

International audienceThe feasibility of geometric magnetoresistance (MR) measurement from linear to saturation operation regime is demonstrated in ultrathin body and BOX fully depleted silicon-on-insulator devices from 14-nm technology node. Besides, we propose a new physical compact model for MOSFET drain current under high field transport, which reproduces experimental MR mobility from linear to saturation operation region and serves as the basis for a new extraction method of carrier saturation velocity. A benchmarking with state-of-the-art saturation velocity extraction methodologies is also conducted. Our saturation velocity results indicate that, for this technology, nonstationary transport prevails as manifested by an overshoot velocity behavior, still far from the ballistic limit

Nuclear magnetic resonance study of the magnetic-field-induced ordered phase in theNiCl2−4SC(NH2)2compound

Nuclear magnetic resonance (NMR) study of the high magnetic field (H) part of the Bose-Einstein condensed (BEC) phase of the quasi-onedimensional (quasi-1D) antiferromagnetic quantum spin-chain compound NiCl2-4SC(NH2)2 (DTN) was performed. We precisely determined the phase boundary, Tc(H), down to 40 mK; the critical boson density, n_c(Tc); and the absolute value of the BEC order parameter S_perp at very low temperature (T = 0.12 K). All results are accurately reproduced by numerical quantum Monte Carlo simulations of a realistic three-dimensional (3D) model Hamiltonian. Approximate analytical predictions based on the 1D Tomonaga-Luttinger liquid description are found to be precise for Tc(H), but less so for S_perp(H), which is more sensitive to the strength of 3D couplings, in particular close to the critical field. A mean-field treatment, based on the Hartree-Fock-Popov description, is found to be valid only up to n_c = 4% (T &lt; 0.3 K), while for higher n_c boson interactions appear to modify the density of states

Magnetic impurities in the pnictide superconductor Ba1-xKxFe2As2

Nuclear magnetic resonance (NMR) measurements have been performed on single crystals of Ba1−xKxFe2As2 (x=0, 0.45) and CaFe2As2 grown from Sn flux. The Ba-based pnictide crystals contain significant amounts of Sn in their structure, ∼1%, giving rise to magnetic impurity effects evident in the NMR spectrum and in the magnetization. Our experiments show that the large impurity magnetization is broadly distributed on a microscopic scale, generating substantial magnetic field gradients. There is a concomitant 20% reduction in the transition temperature, which is most likely due to magnetic electron scattering. We suggest that the relative robustness of superconductivity (x=0.45) in the presence of severe magnetic inhomogeneity might be accounted for by strong spatial correlations between impurities, such as clustering on the coherence length scale.This article is published as Mukhopadhyay, Sutirtha, Sangwon Oh, A. M. Mounce, Moohee Lee, W. P. Halperin, N. Ni, S. L. Bud'ko, P. C. Canfield, A. P. Reyes, and P. L. Kuhns. "Magnetic impurities in the pnictide superconductor Ba1− xKxFe2As2." New Journal of Physics 11, no. 5 (2009): 055002. DOI: 10.1088/1367-2630/11/5/055002. Copyright 2009 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. CC BY 3.0. Posted with permission