Spin gaps and magnetic structure of NaxCoO2

We present two experiments that provide information on spin anisotropy and the magnetic structure of NaxCoO2. First, we report low-energy neutron inelastic scattering measurements of the zone-center magnetic excitations in the magnetically ordered phase of Na0.75CoO2. The energy spectra suggest the existence of two gaps, and are very well fitted by a spin-wave model with both in-plane and out-of-plane anisotropy terms. The gap energies decrease with increasing temperature and both gaps are found to have closed when the temperature exceeds the magnetic ordering temperature T_m~22 K. Secondly, we present neutron diffraction studies of Na0.85CoO2 with a magnetic field applied approximately parallel to the c axis. For fields in excess of ~8T a magnetic Bragg peak was observed at the (0,0,3) position in reciprocal space. We interpret this as a spin-flop transition of the A-type antiferromagnetic structure, and we show that the spin-flop field is consistent with the size of the anisotropy gap.Comment: 9 pages, 7 figure

Further analysis of the quantum critical point of Ce1−x_{1-x}Lax_{x}Ru2_{2}Si2_{2}

New data on the spin dynamics and the magnetic order of Ce$_{1-x}$La$_{x}$Ru$_{2}$Si$_{2}$ are presented. The importance of the Kondo effect at the quantum critical point of this system is emphasized from the behaviour of the relaxation rate at high temperature and from the variation of the ordered moment with respect to the one of the N\'eel temperature for various $x$.Comment: Contribution for the Festschrift on the occasion of Hilbert von Loehneysen 60 th birthday. To be published as a special issue in the Journal of Low Temperature Physic

Superconductivity in Ce- and U-based "122" heavy-fermion compounds

This review discusses the heavy-fermion superconductivity in Ce- and U-based compounds crystallizing in the body-centered tetragonal ThCr2Si2 structure. Special attention will be paid to the theoretical background of these systems which are located close to a magnetic instability.Comment: 12 pages, 9 figures. Invited topical review (special issue on "Recent Developments in Superconductivity") Metadata and references update

X-Ray Magnetic Circular Dichroism and Compton Scattering: Application to 5f Electron Systems

The basic properties of magnetism depend strongly on the spin and orbital components of magnetization. Information about the magnetic moments can be gained using new techniques, like X-ray magnetic circular dichroism or Compton scattering, developed at third-generation synchrotron sources. After a brief introduction to the basic principles of these new magnetic tools, examples of experiments on 5f-electron based systems are presented

X-Ray Magnetic Circular Dichroism and Compton Scattering: Application to 5f Electron Systems

The basic properties of magnetism depend strongly on the spin and orbital components of magnetization. Information about the magnetic moments can be gained using new techniques, like X-ray magnetic circular dichroism or Compton scattering, developed at third-generation synchrotron sources. After a brief introduction to the basic principles of these new magnetic tools, examples of experiments on 5f-electron based systems are presented

The microscopic magnetisation of the superconductor PuCoGa5

The intermetallic compound PuCoGa5 is a superconductor with a surprisingly high critical temperature of in which the superconductivity has been suggested to arise from magnetic fluctuations. We investigated the microscopic magnetic properties by polarised neutron diffraction on a single crystal of 242PuCoGa5. An induced moment is observed on both the Pu and the Co sites. The total magnetisation is significantly smaller than previously reported in agreement with recent magnetisation measurements. This result challenges the currently discussed models for the superconductivity in this weakly magnetic compound.http://www.sciencedirect.com/science/article/B6TJJ-4M8763X-14/1/4d5a078f07a464bafcfba90734b09fc

Magnetism under pressure with synchrotron radiation

The magnetic properties of materials depend strongly on the distance between ions and on the volume available for each magnetic ion. In this article, we introduce a bird's eye view of the various possible effects of pressure on the magnetic state and the consequences of these effects on the fundamental understanding of the magnetism in condensed matter and on the physics and chemistry of minerals in the interior of the Earth and planets. We will give basic information about the ex- perimental possibilities offered by synchrotron-radiation-based techniques in order to explore the magnetic state of matter at high pressure, their interest and feasi- bility. Finally, we will present some experimental highlights where x-ray techniques using synchrotron radiation have been successfully applied to show and explain the magnetic state of matter at high density

Pressure dependence of magnetic transitions in URu₂Si₂

Proceedings of the Third European Conference on Neutron ScatteringNeutron-scattering and specific-heat measurements of the heavy-fermion superconductor URu2Si2 under hydrostatic pressure and with Rh-doping U(Ru0.98Rh0.02)2Si2 show the existence of two magnetic phase transitions: a second-order phase transition with a tiny ordered moment and a first-order phase transition which gives rise to a large moment. The results can be understood in terms of a hidden order parameter ψ linearly coupled to the dipolar ordered moment m