Q. Qian

Multielement spectrometer for efficient measurement of the momentum transfer dependence of inelastic x-ray scattering

Nonresonant x-ray Raman scattering (XRS) is the inelastic scattering of hard x rays from the K shell of low-Z elements or the less tightly bound shells of heavier elements. In the limit of low momentum transfer q, XRS is determined by the same transition matrix element as is measured by x-ray absorption spectroscopies. However, XRS at higher q can often access higher order multipole transitions which help separate the symmetry of various contributions to the local density of states. The main drawback of XRS is its low cross section—a problem that is compounded for a q-dependent study. To address this issue, we have constructed a multielement spectrometer to simultaneously measure XRS at ten different values of q. By means of example, we report new measurements of the XRS from the L- and K-edges of Mg. This instrument is now available to general users at the Advanced Photon Source as the lower energy resolution inelastic x-ray scattering (LERIX) spectrometer.

Local magnetic ordering in La1−xCaxMnO3 determined by spin-polarized x-ray absorption spectroscopy

A systematic study of spin-dependent Mn K-edge x-ray absorption spectra was performed on La1−xCaxMnO3. By examining the changes in the pre-edge spectra with the temperature, a model of the excitation process is developed and used to predict the temperature dependent changes in the local magnetic ordering about Mn sites. The approach is of general applicability to perovskite systems. It can be used to determine the change in the local magnetic order (ferromagnetic versus antiferromagnetic) about a transition metal site upon going through a transition or as the result of external perturbations.

Valence measurement of Mn oxides using Mn Kβ emission spectroscopy

Abstract High resolution Mn K β emission spectra provide a direct method to probe the effective spin state and charge density on Mn sites. Direct comparison of MnF 2 and MnO reveals significant changes due to the degree of covalency. The detailed shape and energy shift of the spectra for the perovskite LaMnO 3 and CaMnO 3 compounds are found to be very similar to Mn 2 O 3 and MnO 2 , respectively. Detailed Mn K β X-ray emission results on La 1− x Ca x MnO 3 can be well fit by linear superpositions of the end member spectra. However, for x 2+ is found.

Structural, magnetic, and transport studies of La0.8MnO3 films

A study of the properties of La0.8MnO3 films of varying thickness was performed. Transport and magnetization measurements show that the ferromagnetic (metallic) volume fraction of the film varies from ∼ 1/4 for ultrathin 60  A films to ∼ 1/2 for 1600  A films. Multilength scale structural measurements reveal that near 300  A, a transition from highly strained ultrathin films to relaxed bulk-like films occurs. The transition region is characterized by low surface roughness, high crystallite orientation, and broad d-spacing distributions.

Structural studies of annealed ultrathin La0.8MnO3 films

A detailed study of the long-range, nanoscale, and local structure of La0.8MnO3 films of varying thickness was performed. These measurements give insight on the relative volumes of the insulating and metallic regions. A thin metallic surface region is found in all films. The nature of the film growth is also discussed.

Observation of strain and temperature induced changes in the band structure of thin La0.8MnO3−δ films

Mn K-edge resonant inelastic x-ray scattering measurements were performed on films of La0.8MnO3−δ. The measurements reveal that strain causes large shifts of the bands above the Fermi level. The Mn 3d band switches from a narrow upshifted peak at high temperature to a broad bulklike band at low temperature in ultrathin films. The strain induced switching behavior opens the possibility of tuning the transition to higher temperatures for device applications in this class of manganite materials.

Multi-element Analyzer for Inelastic X-Ray Scattering

A nine‐element analyzer‐system for inelastic x‐ray scattering has been designed and built. Each individual analyzer crystal is aligned with an inverse joy‐stick goniometer. The energy of the scattered photons is measured with a conventional double‐circle goniometer mounted on a translation stage, which allows the maintenance of the sample, analyzers and detector, also mounted on a separate translation stage, on a Rowland‐circle.