Mechanism Behind the Enhanced Ferromagnetic Contributions Upon Ru Substitution in CaMnO from X-Ray Absorption Spectroscopies.

We have studied the local structure and electronic and magnetic properties of hybrid improper ferroelectric CaMnO upon Ru substitution at the Mn site by a combination of atomic-selective X-ray absorption spectroscopies in the soft and hard X-ray energy regimes. Ru substitution enhances the macroscopic ferromagnetic contributions, whose origin is here elucidated. In particular, soft X-ray magnetic circular dichroism (XMCD) data indicate that the spin moments of Mn and Ru are aligned in opposite directions, with the effective magnetic moments of Ru being about 1 order of magnitude smaller than for Mn.

Temperature-Driven Self-Doping in Magnetite.

Magnetite is one of the most fascinating materials exhibiting the enigmatic first-order Verwey transition which is conventionally manipulated through chemical doping. Here, we show that heating magnetite results in a spontaneous charge reordering and, consequently, a hole self-doping effect at the octahedral sublattice. Core-level x-ray spectroscopy measurements combined with theory uncovers that there are three regimes of self-doping that map the temperature dependence of the electrical conductivity and magnetism up to the Curie temperature.

The five-analyzer point-to-point scanning crystal spectrometer at ESRF ID26.

X-ray emission spectroscopy in a point-to-point focusing geometry using instruments that employ more than one analyzer crystal poses challenges with respect to mechanical design and performance. This work discusses various options for positioning the components and provides the formulas for calculating their relative placement. Ray-tracing calculations were used to determine the geometrical contributions to the energy broadening including the source volume as given by the beam footprint on the sample.

Relation among Oxygen Stoichiometry, Structure, and Co Valence and Spin State in Single-Layer LaACoO (A = Ca, Sr) Perovskites.

We have investigated the role of oxygen stoichiometry and structural properties in the modulation of Co valence and spin state in single-layer LaACoO (A = Sr, Ca; 0 ≤ ≤ 1) perovskites as well as the interplay between their local structural properties and the magnetic and charge-ordering phenomena. We show the results of high angular resolution powder X-ray diffraction and Co -edge X-ray absorption and emission spectroscopy experiments on polycrystalline and single-crystal samples. The different doping-induced changes in the Co valence and spin state by Ca (or Sr) substitution can be understood in terms of the evolving oxygen stoichiometry.

Chemical Sensitivity of Kβ and Kα X-ray Emission from a Systematic Investigation of Iron Compounds.

K-fluorescence X-ray emission spectroscopy (XES) is receiving growing interest in all fields of natural sciences to investigate the local spin. The spin sensitivity in Kβ (Kα) XES stems from the exchange interaction between the unpaired 3p (2p) and the 3d electrons, which is greater for Kβ than for Kα. We present a thorough investigation of a large number of iron-bearing compounds.

New reflections on hard X-ray photon-in/photon-out spectroscopy.

Analysis of the electronic structure and local coordination of an element is an important aspect in the study of the chemical and physical properties of materials. This is particularly relevant at the nanoscale where new phases of matter may emerge below a critical size. X-ray emission spectroscopy (XES) at synchrotron radiation sources and free electron lasers has enriched the field of X-ray spectroscopy.

Selective magnetometry of superparamagnetic iron oxide nanoparticles in liquids.

We show that the properties of superparamagnetic iron oxide nanoparticles suspended in liquids can be effectively studied using Magnetic Circular Dichroism in Resonant Inelastic X-ray Scattering. Analysis of the spectral shape and magnetic contrast produced by this experiment enables an assessment of the site distribution and magnetic state of metal ions in the spinel phase. The selective magnetization profile of particles as derived from the field dependence of dichroism empowers an estimation of particle size distribution.

Noncollinear Ordering of the Orbital Magnetic Moments in Magnetite.

The magnitude of the orbital magnetic moment and its role as a trigger of the Verwey transition in the prototypical Mott insulator, magnetite, remain contentious. Using 1s2p resonant inelastic x-ray scattering angle distribution (RIXS-AD), we prove the existence of noncollinear orbital magnetic ordering and infer the presence of dynamical distortion creating a polaronic precursor for the metal to insulator transition. These conclusions are based on a subtle angular shift of the RIXS-AD spectral intensity as a function of the magnetic field orientation.

Magnetic Contrast at Spin-Flip Excitations: An Advanced X-Ray Spectroscopy Tool to Study Magnetic-Ordering.

The determination of the local orientation and magnitude of the magnetization in spin textures plays a pivotal role in understanding and harnessing magnetic properties for technological applications. Here, we show that by employing the polarization dependence of resonant inelastic X-ray scattering (RIXS), we can directly probe the spin ordering with chemical and site selectivity. Applied on the prototypical ferrimagnetic mixed-valence system, magnetite ([Fe][Fe,Fe]O), we can distinguish spin-flip excitations at the A and B antiferromagnetically coupled Fe sublattices and quantify the exchange field.

Effects of A-site disorder in the properties of A2CoMnO6 (A = La, Tb).

We have studied the structural and physical properties of the La2-xTbxCoMnO6 series. The crystal and magnetic structures of these compounds were determined by x-ray and neutron diffraction techniques. All samples belong to the family of double perovskites with space group P21/n, but the Co/Mn ordering is not perfect, and antisite defects are formed.

Enhancement of ferromagnetic correlations on multiferroic TbMnO₃ by replacing Mn with Co.

The structural, electronic and magnetic properties of TbMn(1-x)Co(x)O(3) (0.1 ≤ x ≤ 0.9) compounds are reported.

Structural properties of Pb2MnW(1-x)Re(x)O6 double perovskites.

Pb2MnW(1-x)Re(x)O6 samples have been synthesized and their structure determined by powder x-ray diffraction. These samples undergo a first order structural phase transition between 413 and 445 K depending on the composition. Above this temperature, the samples are cubic.

Origin of the pre-peak features in the oxygen K-edge x-ray absorption spectra of LaFeO₃ and LaMnO₃ studied by Ga substitution of the transition metal ion.

We report on experimental oxygen K-edge x-ray absorption near edge structure (XANES) spectra of the LaFe(1 - x)Ga(x)O(3) and LaMn(1 - x)Ga(x)O(3) series. Transition metal substitution by the 3d full shell Ga atom is mainly reflected in a systematic decrease of the pre-edge structures in the XANES spectra of the two series. This result shows that the associated states originate from the hybridization of oxygen 2p and unoccupied Fe (or Mn) 3d states.

A new type of antiferrodistortive structure in a double perovskite with Pb.

We have found a new structural transition in Pb(2)MnReO(6) at 410 K. Above this temperature, Pb(2)MnReO(6) is cubic with disordered and dynamic atomic displacements manifested in the large thermal parameters of Pb and O atoms. Below 410 K, the antiferrodistortive shift of 2/3 of Pb(2+) cations away from the high-symmetry cubic site produces a new type of monoclinic cell.