Energy-dispersive X-ray absorption spectroscopy at LNLS: investigation on strongly correlated metal oxides

Abstract

An energy-dispersive X-ray absorption spectroscopy beamline mainly dedicated to X-ray magnetic circular dichroism (XMCD) and material science under extreme conditions has been implemented in a bending-magnet port at the Brazilian Synchrotron Light Laboratory. Here the beamline technical characteristics are described, including the most important aspects of the mechanics, optical elements and detection set-up. The beamline performance is then illustrated through two case studies on strongly correlated transition metal oxides: an XMCD insight into the modifications of the magnetic properties of Cr-doped manganites and the structural deformation in nickel perovskites under high applied pressure.

Stability of Ni sites across the pressure-induced insulator-to-metal transition in YNiO3

“…In a dispersive XAS setup the monochromator does not move allowing a very high energy stability. During the whole experiment, a sharp Bragg peak outside the analysis range allowed us to verify that the energy stability was better than 50 meV, in accordance with previous measurements 20 .…”

Compensation temperatures and exchange bias inLa1.5Ca0.5CoIrO6

“…XPS experiments were performed using an ultra-high vacuum (UHV) chamber equipped with a SPECS analyzer PHOIBOS 150. XMCD and XANES measurements were performed in the dispersive x-ray absorption (DXAS) beam line at the Brazilian Synchrotron Light Laboratory (LNLS) [15]. The edge step normalization of the data was performed after a linear pre-edge subtraction and the regression of a quadratic polynomial beyond the edge, using the software ATHENA [16].…”

Emergence of ferromagnetism and Jahn-Teller distortion in LaMn1−xCrxO3Ramos1, Tolentino2, Soares3 et al. 2013Phys. Rev. BSelf Cite21180View full textAdd to dashboardCite

“…Cr dopants can also be viewed as a quenched random field 8,9 . However direct x-ray magnetic circular dichroism experiments suggest that the exchange interaction between M n 3+ and Cr 3+ leads to a net local antiparallel coupling [12][13][14][15] , regardless of the magnetic state nature of the manganite compound. This scenario is supported by spin resonance investigations 16 .…”

“…These features make the partial substitution of M n by Cr in LaM nO 3.00+δ an interesting system for studying the close relationship between Jahn Teller (JT) distortion, double exchange (DE) and superexchange (SE) interactions and orbital degeneracy. Since the first studies of the series LaM n 1−x Cr x O 3 in the 1950s 2,3 it is known that upon Cr-doping the antiferromagnetic (AFM) Mott insulator LaM nO 3 develops a ferromagnetic (FM) component, but the character of the M n 3+ − Cr 3+ interaction has been under debate for a long time 1,2,[4][5][6][7][8][9][10][11][12][13][14][15][16] . A M n 3+ -Cr 3+ SE FM coupling may account for the increasing Curie temperature and spontaneous magnetization with increasing Cr doping [4][5][6][7] .…”

“…The XMCD signals resulting from several scans were added and normalized to the absorption jump. Slight differences between the signals collected in the transmission (temperature dependent Mn K XMCD) and the fluorescence modes (coupled 10 K XMCD at Mn and Cr K edges) arise from differences in the amplitude of the contribution of La edge 15 . At the Cr K edge, specially, the signal is superimposed to a large background contribution of the La L 2 edge signal.…”