Magnetic properties of pure and Gd doped EuO probed by NMR

An Eu NMR study in the ferromagnetic phase of pure and Gd doped EuO was performed. A complete description of the NMR lineshape of pure EuO allowed for the influence of doping EuO with Gd impurities to be highlighted. The presence of a temperature dependent static magnetic inhomogeneity in Gd doped EuO was demonstrated by studying the temperature dependence of the lineshapes. The results suggest that the inhomogeneity in 0.6% Gd doped EuO is linked to colossal magnetoresistance. The measurement of the spin-lattice relaxation times as a function of temperature led to the determination of the value of the exchange integral J as a function of Gd doping. It was found that J is temperature independent and spatially homogeneous for all the samples and that its value increases abruptly with increasing Gd doping.Comment: 14 pages, 10 figures, to be published in Physical Review

Anomalous behavior of the spin gap of a spin-1/2 two-leg antiferromagnetic ladder with Ising-like rung interactions

Using mainly numerical methods, we investigate the width of the spin gap of a spin-1/2 two-leg ladder described by \cH= J_\rl \sum_{j=1}^{N/2} [ \vS_{j,a} \cdot \vS_{j+1,a} + \vS_{j,b} \cdot \vS_{j+1,b} ] + J_\rr \sum_{j=1}^{N/2} [\lambda (S^x_{j,a} S^x_{j,b} + S^y_{j,a} S^y_{j,b}) + S^z_{j,a} S^z_{j,b}] , where $S^\alpha_{j,a(b)}$ denotes the $\alpha$-component of the spin-1/2 operator at the $j$-th site of the $a (b)$ chain. We mainly focus on the J_\rr \gg J_\rl > 0 and $|\lambda| \ll 1$ case. The width of the spin gap as a function of $\lambda$ anomalously increases near $\lambda = 0$; for instance, for $-0.1 < \lambda < 0.1$ when $J_{\rm l}/J_{\rm r} = 0.1$. The gap formation mechanism is thought to be different for the $\lambda 0$ cases. Since, in usual cases, the width of the gap becomes zero or small at the point where the gap formation mechanism changes, the above gap-increasing phenomenon in the present case is anomalous. We explain the origin of this anomalous phenomenon by use of the degenerate perturbation theory. We also draw the ground-state phase diagram.Comment: 4 pages, 11 figures; Proc. "The International Conference on Quantum Criticality and Novel Phases" (2012), to be published in Phys. Stat. Solidi

Time-dependent correlation function of the Jordan-Wigner operator as a Fredholm determinant

We calculate a correlation function of the Jordan-Wigner operator in a class of free-fermion models formulated on an infinite one-dimensional lattice. We represent this function in terms of the determinant of an integrable Fredholm operator, convenient for analytic and numerical investigations. By using Wick's theorem, we avoid the form-factor summation customarily used in literature for treating similar problems.Comment: references added, introduction and conclusion modified, version accepted for publication in J. Stat. Mec

The phase transition in the localized ferromagnet EuO probed by muSR

We report results of muon spin rotation measurements performed on the ferromagnetic semiconductor EuO, which is one of the best approximations to a localized ferromagnet. We argue that implanted muons are sensitive to the internal field primarily through a combination of hyperfine and Lorentz fields. The temperature dependences of the internal field and the relaxation rate have been measured and are compared with previous theoretical predictions.Comment: 4 pages, 4 figure

On the Two-Point Correlation Function in Dynamical Scaling and SCHR\"Odinger Invariance

The extension of dynamical scaling to local, space-time dependent rescaling factors is investigated. For a dynamical exponent $z=2$, the corresponding invariance group is the Schr\"odinger group. Schr\"odinger invariance is shown to determine completely the two-point correlation function. The result is checked in two exactly solvable models.Comment: Geneva preprint UGVA/DPT 1992/09-783, plain Tex 6pp (to appear in Int. J. Mod. Phys. C

Magnetic Excitations of the 2-D Sm Spin Layers in Sm(La,Sr)CuO4

We present specific heat and susceptibility data on Sm(La,Sr)CuO4 in magnetic fields up to 9 T and temperatures down to 100 mK. We find a broad peak in specific heat which is insensitive to magnetic field at a temperature of 1.5 K with a value of 2.65 J/mol K. The magnetic susceptibility at 5 T continues to increase down to 2 K, the lowest temperature measured. The data suggest that the Sm spin system may be an ideal realization of the frustrated Heisenberg antiferromagnet on the square lattice.Comment: 2 pages, 2 figures, submitted to IC

Results of charged pions cross-section in proton carbon interaction at 31 GeV/c measured with the NA61/SHINE detector

Among other goals, the NA61/SHINE (SHINE=SPS Heavy Ion and Neutrino Experiment) detector at CERN SPS aims at precision hadro-production measurements to characterise the neutrino beam of the T2K experiment at J-PARC. These measurements are performed using a 31 GeV/c proton beam produced at the SPS with a thin carbon target and a full T2K replica target. Spectra of charged pion inclusive inelastic cross section were obtained from pilot data collected in 2007 1 with a 2 cm thick target (4% of the interaction length). The SHINE detector and its particle identification capabilities are described and the analysis techniques are briefly discussed

Preliminary results of charged pions cross-section in proton carbon interaction at 30 GeV measured with the NA61/SHINE detector

As the intensity of neutrino beams produced at accelerators increases, important systematic errors due to poor knowledge of production cross sections for pions and kaons arise. Among other goals, the NA61/SHINE (SHINE=SPS Heavy Ion and Neutrino Experiment) detector at CERN SPS aims at precision hadro-production measurements to characterise the neutrino beam of the T2K experiment at J-PARC. These measurements are performed using a 30GeV proton beam produced at the SPS with a thin carbon target and a full T2K replica target. Preliminary spectra of $\pi^{+}$ and $\pi^{-}$ inclusive cross section were obtained from pilot data collected in 2007 with a 2 cm thick target. After a description of the SHINE detector and its particle identification capabilities, results from three different analysis are discussed

Scattering theory of interface resistance in magnetic multilayers

The scattering theory of transport has to be applied with care in a diffuse environment. Here we discuss how the scattering matrices of heterointerfaces can be used to compute interface resistances of dirty magnetic multilayers. First principles calculations of these interface resistances agree well with experiments in the CPP (current perpendicular to the interface plane) configuration.Comment: submitted to J. Phys. D (special issue at the occasion of Prof. T. Shinjo's 60th birthday