B. Hennion

EVIDENCE FOR INCOMMENSURATE SPIN FLUCTUATIONS IN SR2RUO4

We report first inelastic neutron scattering measurements in the normal state of Sr_2RuO_4 that reveal the existence of incommensurate magnetic spin fluctuations located at

Phonons in YBa2Cu3O7-δ

{\bf q}_0=(\pm 0.6\pi/a, \pm 0.6\pi/a, 0)

Effect of Tethered Chains on Adhesion

. This finding confirms recent band structure calculations that have predicted incommensurate magnetic responses related to dynamical nesting properties of its Fermi surface.

Neutron diffraction study of (Ce, La)Ru2Si2 alloys in an external field

Abstract By inelastic neutron scattering the phonon dispersion curves in YBa 2 Cu 3 O 7 and YBa 2 Cu 3 O 6 were investigated. Based on these results the differences in the phonon densities of states of the two compounds are analyzed.

Magnetic order and canting in a reentrant alloy studied by magnetization, mössbauer and neutron scattering

The influence of magnetic (S=1) and nonmagnetic (S=0) impurities on the spin dynamics of an optimally doped high temperature superconductor is compared in YBa2(Cu0.97Ni0.03)3O7 (Tc=80 K) and YBa2(Cu0.99Zn0.01)3O7 (Tc=78 K). In the Ni-substituted system, the magnetic resonance peak (which is observed at Er approximately 40 meV in the pure system) shifts to lower energy with a preserved Er/Tc ratio while the shift is much smaller upon Zn substitution. By contrast Zn, but not Ni, restores significant spin fluctuations around 40 meV in the normal state. These observations are discussed in the light of models proposed for the magnetic resonance peak.

New excitations in quantum paraelectrics

Abstract The magnetic phase diagram of Ce1−xLaxRu2Si2 alloys (x = 0.20 and 0.30) has been determined by neutron diffraction. Besides the zero-field incommensurate modulated structure (k1 = [0.31, 0, 0]) and the polarized paramagnetic state, two additional phases are observed: another incommensurate structure and a commensurate one ( k 3 = [ 1 3 , 1 3 , 0] ). The magnetic modulation at H = 0 remains practically unaffected by La dilution up to x = 0.80.

Magnetic excitations in the antiferromagnetic Kondo compound CePd2Si2

Abstract Inelastic neutron scattering and Mossbauer measurements have been carried out on the reentrant alloy (Fe0.765Mn0.235)75P16B6Al3, using samples from the same ribbon. The canting temperature deduced from Mossbauer data coincides with the appearance of a central peak in the inelastic neutron scattering. Polarized neutron transmission experiments are consistent with a ferromagnetic domain-like structure at all temperatures below the Curie point.

Spin dynamics in YBa2(Cu0.98Zn0.02)3O6.7

Abstract Three remarkable anomalies related to the acoustic branches of quantum paraelectric (QPE) oxides are presented. In SrTiO 3 , an additional shear-like sheet is observed for modes propagating in the tetragonal plane, and shear branches polarized parallel to the tetragonal axis show an anomalous softening on cooling in the QPE-regime. Both in SrTiO 3 and KTaO 3 , a new doublet is observed in Brillouin scattering which is due to second sound, the wave-like propagation of heat. These effects are discussed in terms of large anharmonic polarization clusters.

Magnetic defects observed by small angle neutron scattering in applied magnetic fields in a weakly frustrated system

Abstract The magnetic excitations of the Kondo compound CePd 2 Si 2 below its Neel temperature ( T N = 10 K) have been studied by inelastic neutron scattering. At T = 1.6 K the data are best represented by two dispersive inelastic modes. Their linewidth (∼ 0.5 meV) indicates substantial broadening, which is ascribed to Kondo-type local fluctuations.

Unusual spin dynamics in the doped antiferromagnetic phase of YBa2(Cu0.98Zn0.02)3O6.39

Inelastic neutron scattering has been used to study the spin dynamics in underdoped zinc-substituted YBa2(Cu0.98Zn0.02)3O6.7 (TC=17 K). Zinc substitution in CuO2 planes may induce a localization of carriers at low temperature as a strong enhancement of the low energy magnetic excitations is observed below 80 K removing the “spin-gap”. In contrast, a magnetic pseudo gap is still sizeable above 100 K.