J. M. Tonnerre

Role of magnetic and orbital ordering at the metal-insulator transition in NdNiO{sub 3}

Soft x-ray resonant scattering at the Ni L{sub 2,3} edges is used to test models of magnetic- and orbital-ordering below the metal-insulator transition in NdNiO{sub 3}. The large branching ratio of the L{sub 3} to L{sub 2} intensities of the (1/2 0 1/2) reflection and the observed azimuthal angle and polarization dependence originates from a noncollinear magnetic structure. The absence of an orbital signal and the noncollinear magnetic structure show that the nickelates are materials for which orbital ordering is absent at the metal-insulator transition.

Structural and magnetic properties of CoPt mixed clusters

In this present work, we report a structural and magnetic study of mixed Co58Pt42 clusters. MgO, Nb and Si matrix can be used to embed clusters, avoiding any magnetic interactions between particles. Transmission Electron Microscopy (TEM) observations show that Co58Pt42 supported isolated clusters are about 2nm in diameter and crystallized in the A1 fcc chemically disordered phase. Grazing Incidence Small Angle X-ray Scattering (GISAXS) and Grazing Incidence Wide Angle X-ray Scattering (GIWAXS) reveal that buried clusters conserve these properties, interaction with matrix atoms being limited to their first atomic layers. Considering that 60% of particle atoms are located at surface, this interactions leads to a drastic change in magnetic properties which were investigated with conventional magnetometry and X-Ray Magnetic Circular Dichroism (XMCD). Magnetization and blocking temperature are weaker for clusters embedded in Nb than in MgO, and totally vanish in silicon as silicides are formed. Magnetic volume of clusters embedded in MgO is close to the crystallized volume determined by GIWAXS experiments. Cluster can be seen as a pure ferromagnetic CoPt crystallized core surrounded by a cluster-matrix mixed shell. The outer shell plays a predominant role in magnetic properties, especially for clusters embedded in niobium which have a blocking temperature 3 times smaller than clusters embedded in MgO.

The SEXTANTS beamline at SOLEIL: a new facility for elastic, inelastic and coherent scattering of soft X-rays

SEXTANTS is a new SOLEIL beamline dedicated to soft X-ray scattering techniques. The beamline, covering the 50-1700 eV energy range, features two Apple-II undulators for polarization control and a fixed-deviation monochromator. Two branch-lines host three end-stations for elastic, inelastic and coherent scattering experiments.

Manipulating 4 f quadrupolar pair-interactions in Tb B 2 C 2 using a magnetic field

Resonant soft x-ray Bragg diffraction at the Tb M4,5 edges and non resonant Bragg diffraction have been used to investigate orbitals in TbB2C2. The Tb 4f quadrupole moments are ordered in zero field below T_N and show a ferroquadrupolar alignment dictated by the antiferromagnetic order. With increasing applied field along [110] the Tb 4f magnetic dipole moments rotate in a gradual manner toward the field. The quadrupole moment is rigidly coupled to the magnetic moment and follows this field-induced rotation. The quadrupolar pair interaction is found to depend on the specific orientation of the orbitals as predicted theoretically and can be manipulated with an applied magnetic field.

Strong noncollinearity between nonequivalent Nd magnetic moments in Nd2Fe14B at low temperature

A temperature-dependent x-ray resonant magnetic scattering study through the spin reorientation transition (SRT) that Nd2Fe14B undergoes below TSRT=135 K is presented. The experimental results evidence a strong noncollinearity between the magnetic moments of Nd atoms in 4f and 4g crystallographic sites in the low-temperature phase.

X-ray anomalous diffraction and resonant magnetic scattering X-ray study of FexMn1−x/Ir(001) superlattices

Abstract X-ray anomalous diffraction in different geometries and X-ray resonant magnetic scattering have been used to investigate Fe x Mn 1− x /Ir(001) superlattices. The influence of the alloy stoichiometry on the structural and magnetic properties has been studied and compared with the bulk alloy properties. The structural results are compared with the magnetic results in order to understand the outstanding properties of these systems.

5d and 4f Magnetic Profiles in Ce/Fe Multilayers Probed by XRMS

The element and electronic shell specificities of x-ray resonant magnetic scattering have been used to investigate the induced magnetization of the 5d and 4f electronic states of Ce in a [Ce(10A)/Fe(30A)]×100 multilayer. We show that the measurement of the magnetic contribution to the intensities diffracted at low angles at the L2 and M4 edge of the rare-earth allows to investigate the profile of the 5d and 4f magnetic polarisation across the rare-earth layer. The Ce 5d polarization is found to be oscillating across the Ce layer with a slow decrease from the interfaces with Fe towards the center of the layer. Preliminary results on the Ce 4f polarisation indicate a constant profile.

Manipulating4fquadrupolar pair-interactions inTbB2C2using a magnetic field

Resonant soft x-ray Bragg diffraction at the Tb M4,5 edges and non resonant Bragg diffraction have been used to investigate orbitals in TbB2C2. The Tb 4f quadrupole moments are ordered in zero field below T_N and show a ferroquadrupolar alignment dictated by the antiferromagnetic order. With increasing applied field along [110] the Tb 4f magnetic dipole moments rotate in a gradual manner toward the field. The quadrupole moment is rigidly coupled to the magnetic moment and follows this field-induced rotation. The quadrupolar pair interaction is found to depend on the specific orientation of the orbitals as predicted theoretically and can be manipulated with an applied magnetic field.

Manipulating 4f quadrupolar pair-interactions in TbB2C2 using a magnetic field

Resonant soft x-ray Bragg diffraction at the Tb M4,5 edges and non resonant Bragg diffraction have been used to investigate orbitals in TbB2C2. The Tb 4f quadrupole moments are ordered in zero field below T_N and show a ferroquadrupolar alignment dictated by the antiferromagnetic order. With increasing applied field along [110] the Tb 4f magnetic dipole moments rotate in a gradual manner toward the field. The quadrupole moment is rigidly coupled to the magnetic moment and follows this field-induced rotation. The quadrupolar pair interaction is found to depend on the specific orientation of the orbitals as predicted theoretically and can be manipulated with an applied magnetic field.

Resonant inelastic X-ray scattering study of rare-earth electronic excitation on R2Fe14B

Abstract Resonant inelastic X-ray scattering spectra are recorded at the L 3 absorption edge of rare-earth ions in R 2 Fe 14 B. In all cases, weak resonances are observed at energies below the dipolar whiteline, ascribed to 2p → 4f quadrupolar excitations. Their energy position is in excellent agreement with the pre-edge features in the XMCD spectra of the same samples.