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The magnon dispersion for the layered ferromagnet Mn 1 4 TaS 2 has been measured in the 3 high symmetry directions at 0.5Tc by neutron inelastic scattering. Some data on the temperature dependence of this dispersion is also presented. The data have been fitted to a matching matrix element model giving values for exchange constants for 5 neighbours. The spin waves are much stiffer in the c∗ direction than in the basal plane.

Neutron scattering studies have been carried out on high-quality specimens of ZrZn2, giving direct experimental evidence on the nature of low-lying magnetic excitations in an ordered weak metallic ferromagnet both below and above the Curie temperature.

The magnetic ordering in the re-entrant magnetic superconductor Er4.3Rh6Sn18.7 has been examined. Ferromagnetic correlations of ≈60 A are found to develop at low temperatures. There is no evidence for the existence of spiral magnetic ordering in this compound.

La1.85Ba0.15CuO4 is the prototype member of a new class of unusual high temperature (Tc>24K) superconductors. These novel materials whose properties lie at the interface between metallic and insulating behaviour show a wide variety of physical phenomena. For example, the electrical resistivity of the parent compound La2CuO4 shows metallic behaviour down to approxi-mately 25 K where an abrupt upturn occurs towards a semiconduct-ing or insulating state. The barium-doped superconductor exhibits a linear fall in resistivity from room to liquid-nitrogen tem-peratures followed by a plateau to 35 K, at which point supercon-ducting behaviour begins. Several theoretical suggestions regard-ing the origin of this behaviour have been put forward, but the role played by dynamic or static lattice–instabilities is still an area of controversy (see refs 1–4). Evidence for the presence of a tetragonal to orthorhombic phase transition together with further subtle and anomalous structural instabilities in the barium-doped compound has been reported5. To elucidate the correlations between the lattice vibrational and electronic behaviour, we have undertaken neutron inelastic scattering experiments on the High Energy Transfer spectrometer at the ISIS facility of the Rutherford Appleton Laboratory, UK, using carefully prepared polycrystalline samples of both La1.85Ba0.15CuO4 and La2CuO4. The experiments were performed over a range of temperatures between 12 K and 200 K. Here we report anomalous temperature dependence of modes centred at 10 meV and 20 meV respectively.

The dynamical response of the heavy fermion system CePb3 consists of two parts, a narrow quasielastic line and a broad crystal field excitation, the width of each component is strongly temperature dependent. The linewidth of the quasielastic line (Γ) is well represented by the expression Γ 2 =0.17+0.12T 1 2 .

Neutron scattering has been used to determine the magnetic order of the Gd in the oxygen-deficient compound Gd${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6.14}$. The ordering is found to be identical to that found earlier for the superconducting composition by Paul et al. This differs from a result by Chattopadhyay et al., who found a variation in the magnetic structure of the oxygen-deficient compound.

We have investigated single‐crystals growth of Nd2‐xCexCu04‐y By using a flux method. The phase diagram Nd203 ‐CuO has been determined For a number of compositions. In addition, the corresponding diagram for some Nd2O3CeO2‐CuO composition is also reported. Plate single crystals having dimensions up to 5 x 5 x 0.2 m have been prepared by the melt mixtures from 1250℃ to 800℃ at a rate of 5℃/h.The yield of CeO2 concentration in the starting compositions and the corresponding x values in the crystals has been investigated in order to improve superconducting properties of the crystals. Superconducting single crystals have been found from flux compositions 70% CuO, (30‐z)% NdO1.5and z% of CeO2 with 2.50 < z < 4 5.

High-resolution neutron scattering measurements have been made on the high-energy magnetic excitations for Ni for different temperatures. It is shown that these excitations are not strongly affected by temperatures on the order of the Curie temperature. This shows that very high neutron energies must be used if the paramagnetic susceptibility is to be obtained by energy integration of the total scattering.

Magnetic resonance at frequencies 22–75 GHz is investigated in pure single-crystalline CuGeO3 in the temperature range 1.2–25 K. At temperatures below 4 K the magnetic resonance line splits into four spectral components. The line close to the ESR of the paramagnetic phase is associated with impurities or defects. The other three lines have the same intensity in different samples and are apparently characteristic for pure single crystals at low temperature. An antiferromagnetic resonance with two resonance absorption branches and a spectrum characteristic for an antiferromagnet with easy, average, and hard anisotropy axes was observed and investigated in the Neel compound Cu0.98Zn0.02GeO3 with diamagnetic dilution of the spin subsystem.

To trace the origin of time-reversal symmetry breaking (TRSB) in Re-based superconductors, we performed comparative muon-spin rotation/relaxation ($\mu$SR) studies of superconducting noncentrosymmetric Re$_{0.82}$Nb$_{0.18}$ ($T_c = 8.8$ K) and centrosymmetric Re ($T_c = 2.7$ K). In Re$_{0.82}$Nb$_{0.18}$, the low temperature superfluid density and the electronic specific heat evidence a fully-gapped superconducting state, whose enhanced gap magnitude and specific-heat discontinuity suggest a moderately strong electron-phonon coupling. In both Re$_{0.82}$Nb$_{0.18}$ and pure Re, the spontaneous magnetic fields revealed by zero-field $\mu$SR below $T_c$ indicate time-reversal symmetry breaking and thus unconventional superconductivity. The concomitant occurrence of TRSB in centrosymmetric Re and noncentrosymmetric Re$T$ ($T$ = transition metal), yet its preservation in the isostructural noncentrosymmetric superconductors Mg$_{10}$Ir$_{19}$B$_{16}$ and Nb$_{0.5}$Os$_{0.5}$, strongly suggests that the local electronic structure of Re is crucial for understanding the TRSB superconducting state in Re and Re$T$. We discuss the superconducting order parameter symmetries that are compatible with the observations., Comment: 3 figures, 5 pages, accepted by Physical Review Letters

We report the first observation of multigap superconductivity in TaRh$_{2}$B$_{2}$. We show TaRh$_{2}$B$_{2}$ is a bulk type-II superconductor with a transition temperature, $T_{\mathrm{c}} = 6.00(5)$ K. We present transverse-field muon spin relaxation data where the superconducting gap can be fit using a two-gap $\left(s+s\right)$-wave model. We also report the zero-field electronic specific heat in the superconducting state that is best described by the same $\left(s+s\right)$ model providing further evidence of multiband behavior in this superconductor. Zero-field muon spin relaxation measurements show time-reversal symmetry is preserved in the superconducting state. We demonstrate that TaRh$_{2}$B$_{2}$ has an upper critical field of $15.2(1)$ T, which is significantly higher than previously reported and exceeds the Pauli limit., Comment: 5 pages, 3 figures. Accepted for publication in Physical Review B

The flux line lattice inside a single crystal of Bi2.15Sr1.95CaCu2O8+x has been observed using small-angle neutron diffraction. The diffracted intensity goes rapidly to zero at a magnetic-field-dependent flux lattice melting temperature; this melting coincides with the appearance of finite resistance within the superconducting state. The flux lattice signal can also be made to disappear at low temperatures, by applying a sufficiently high field, probably because of the decomposition of flux lines into two-dimensional 'pancake' vortices.