Browsing by Author "Staub, U"
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- ItemCircularly polarized soft x-ray diffraction study of helical magnetism in hexaferrite(American Physical Society, 2010-03-01) Mulders, AM; Lawrence, SM; Princep, AJ; Staub, U; Bodenthin, Y; García-Fernández, M; Garganourakis, M; Hester, JR; Macquart, RB; Ling, CDMagnetic spiral structures can exhibit ferroelectric moments as recently demonstrated in various multiferroic materials. In such cases the helicity of the magnetic spiral is directly correlated with the direction of the ferroelectric moment and measurement of the helicity of magnetic structures is of current interest. Soft x-ray resonant diffraction is particularly advantageous because it combines element selectivity with a large magnetic cross-section. We calculate the polarization dependence of the resonant magnetic x-ray cross-section (electric dipole transition) for the basal plane magnetic spiral in hexaferrite Ba0.8Sr1.2Zn2Fe12O22 and deduce its domain population using circular polarized incident radiation. We demonstrate there is a direct correlation between the diffracted radiation and the helicity of the magnetic spiral. © 2010, American Physical Society
- ItemDirect observation of charge order and an orbital glass state in multiferroic LuFe2O4(American Physical Society, 2009-08-14) Mulders, AM; Lawrence, SM; Staub, U; García-Fernández, M; Scagnoli, V; Mazzoli, C; Pomjakushina, E; Conder, K; Wang, YDGeometrical frustration of the Fe ions in LuFe2O4 leads to intricate charge and magnetic order and a strong magnetoelectric coupling. Using resonant x-ray diffraction at the Fe K edge, the anomalous scattering factors of both Fe sites are deduced from the (h/3 k/3 l/2) reflections. The chemical shift between the two types of Fe ions equals 4.0(1) eV corresponding to full charge separation into Fe2+ and Fe3+. The polarization and azimuthal angle dependence of the superlattice reflections demonstrate the absence of differences in anisotropic scattering revealing random orientations of the Fe2+ orbitals characteristic of an orbital glass state. © 2009, American Physical Society
- ItemDoping and temperature dependence of Mn 3d states in A-site ordered manganites(American Physical Society, 2010-12-06) García-Fernández, M; Staub, U; Bodenthin, Y; Pomjakushin, V; Mirone, A; Fernández-Rodríguez, J; Scagnoli, V; Mulders, AM; Lawrence, SM; Pomjakushina, EWe present a systematic study of the electronic structure in A-site ordered manganites as function of doping and temperature. The energy dependencies observed with soft x-ray resonant diffraction (SXRD) at the Mn L2,3 edges are compared with structural investigations using neutron powder diffraction as well as with cluster calculations. The crystal structures obtained with neutron powder diffraction reflect the various orbital and charge ordered phases, and show an increase in the Mn-O-Mn bond angle as function of doping and temperature. Cluster calculations show that the observed spectral changes in SXRD as a function of doping are more pronounced than expected from an increase in bandwitdh due to the increase in Mn-O-Mn bond angle and are best described by holes that are distributed at the neighboring oxygen ions. These holes are not directly added to the Mn 3d shell but centered at the Mn site. In contrast, the spectral changes in SXRD as function of temperature are best described by an increase of magnetic correlations. This demonstrates the strong correlations between orbitals and magnetic moments of the 3d states. © 2010, American Physical Society
- ItemEvolution of charge order through the magnetic phase transition of LuFe2O4(American Physical Society, 2012-07-13) Bartkowiak, M; Mulders, AM; Scagnoli, V; Staub, U; Pomjakushina, E; Conder, KThe charge order in multiferroic LuFe(2)O(4) has been investigated with resonant x-ray diffraction at the Fe K edge in the combined charge ordered and magnetic phase. The energy dependence of the charge order reflection (1/3 1/3 7/2) has been analyzed in detail to investigate the charge disproportionation between the iron sites as a function of temperature. It is found that the charge disproportionation is constant within 0.02e across the Neel temperature T(N). The charge order reflection exhibits a decrease in intensity with increasing temperature which is attributed to an increase in the probability of electron hopping. We confirm the increase in polarization at T(N) is not of static origin but rather dynamic. Our observations are consistent with antiferromagnetically aligned magnetic moments inhibiting the double exchange mechanism and reducing the probability of electrons hopping between Fe(2+) and Fe(3+) in the magnetic phase. © 2012, American Physical Society.
- ItemInduced noncollinear magnetic order of Nd3+ in NdNiO3 observed by resonant soft x-ray diffraction(American Physical Society, 2008-03) Scagnoli, V; Staub, U; Bodenthin, Y; García-Fernández, M; Mulders, AM; Meijer, GI; Hammerl, GSoft x-ray resonant magnetic diffraction at the Nd M edges was performed on a NdNiO3 epitaxial film to investigate the magnetic ordering of the Nd ions below the metal-insulator transition. A noncollinear magnetic structure induced by the Ni magnetic moments best describes the azimuthal angle dependency of the (1/2, 0, 1/2) reflection. This confirms the Ni spin structure observed with soft x-ray diffraction experiments performed at the Ni L edge, providing further evidence of charge disproportionation without orbital order below the metal-insulator transition in NdNiO3. © 2008, American Physical Society
- ItemMagnetic and electronic co states in the layered cobaltate GdBaCo2O5.5-x(American Physical Society, 2008-08) García-Fernández, M; Scagnoli, V; Staub, U; Mulders, AM; Janousch, M; Bodenthin, Y; Meister, D; Patterson, BD; Mirone, A; Tanaka, Y; Nakamura, T; Grenier, S; Huang, YJ; Conder, KWe have performed nonresonant x-ray diffraction, resonant soft and hard x-ray magnetic diffraction, soft x-ray absorption, and x-ray magnetic circular dichroism measurements to clarify the electronic and magnetic high-spin (HS) state at the states of the Co3+, ions in GdBaCo2O5.5. Our data are consistent with a Co-Py(3+) pyramidal sites and a Co-Oc(3+), low-spin (LS) state at the octahedral sites. The structural distortion with a doubling of the a axis (2a(p)X2a(p)X2a(p) cell) shows alternating elongations and contractions of the pyramids, and indicates that the metal-insulator transition is associated with orbital order in the t(2g) orbitals of the Co-Py(3+) HS state. This distortion corresponds to an alternating ordering of xz and yz orbitals along the a and c axes for the Co-Py(3+). The orbital ordering and pyramidal distortion lead to deformation of the octahedra but the Co-Oc(3+) LS state does not allow an orbital order to occur for the Co-Oc(3+), ions. The soft x-ray magnetic diffraction results indicate that the magnetic moments are aligned in the ab plane but are not parallel to the crystallographic a or b axes. The orbital order and the doubling of the magnetic unit cell along the c axis support a noncollinear magnetic structure. The x-ray magnetic circular dichroism data indicate that there is a large orbital magnetic contribution to the total ordered Co moment. © 2008, American Physical Society
- ItemPolarization analysis in soft x-ray diffraction to study magnetic and orbital ordering(Wiley-Blackwell, 2008-09) Staub, U; Scagnoli, V; Bodenthin, Y; García-Fernández, M; Wetter, R; Mulders, AM; Grimmer, H; Horisberger, MAn experimental approach to the analysis of charge, magnetic and orbital ordering in 3d transition-metal oxides is presented. The technique combines two important components: azimuthal rotations around the Bragg wavevector and polarization analysis of the Bragg intensities in the range 500-900 eV. The polarization analysis is performed using graded multilayers, which are translated and rotated in the vacuum chamber. It is shown why these two components are important to determine the origin of the Bragg scattered signals and how they allow us to separate the different contributions. Examples are given for the oxygen K and the Mn, Co, Ni and Cu L-2,L-3-edges, and the advantages and drawbacks of this experimental technique are discussed. © International Union of Crystallography
- ItemResonant soft x-ray powder diffraction study to determine the orbital ordering in a-site-ordered SmBaMn2O6(American Physical Society, 2008-02) García-Fernández, M; Staub, U; Bodenthin, Y; Lawrence, SM; Mulders, AM; Buckley, CE; Weyeneth, S; Pomjakushina, E; Conder, KSoft x-ray resonant powder diffraction has been performed at the Mn L-2,L-3 edges of A-site-ordered SmBaMn2O6. The energy and polarization dependences of the (1/4 1/4 0) reflection provide direct evidence for a (x(2) - z(2))/(y(2) - z(2))-type orbital ordering in contrast to single-layer manganite. The temperature dependence of the reflection indicates an orbital reorientation transition at approximate to 210 K, below which the charge- and orbital-ordered MnO2 sheets show AAAA-type of stacking. The concurring reduction of the ferromagnetic superexchange correlations leads to further charge localization. © 2008, American Physical Society
- ItemResonant x-ray diffraction and the observation of strange quantities(Australian Institute of Physics, 2012-02-02) Princep, AJ; Mulders, AM; Schierle, E; Weschke, E; Hester, JR; Hutchinson, WD; Tanaka, Y; Terada, N; Narumi, Y; Staub, U; Scagnoli, V; Nakamura, T; Kikkawa, A; Lovesey, SW; Balcar, ECondensed matter physics has a growing reputation for providing an opportunity to observe exotic particles and states of matter that have an analogue in other areas of physics. Examples of this include the observation of Dirac strings and magnetic monopoles in spin-ice materials , spinon / holon separation in gated nanowires , and toroidal moments (anapoles) in the ubiquitous cuprates . Resonant X-ray Diffraction (RXD) is well suited to the observation of a variety of quantities that behave differently under time reversal, coordinate inversion, and rotation . It is possible to distinguish between competing orders and we have determined the orbital order in RB2C2, including higer order terms (as illustrated on the cover page) [5,6]
- ItemTriakontadipole and high-order dysprosium multipoles in the antiferromagnetic phase of DyB2C2(IOP Publishing Ltd., 2011-07-06) Princep, AJ; Mulders, AM; Staub, U; Scagnoli, V; Nakamura, T; Kikkawa, A; Lovesey, SW; Balcar, EResonant soft x-ray Bragg diffraction at the Dy M-4,M-5 edges has been used to study Dy multipoles in the combined magnetic and orbitally ordered phase of DyB2C2. The analysis incorporates both the intra-atomic magnetic and quadrupolar interactions between the 3d core and 4f valence shells. Additionally, we introduce to the formalism the interference of magnetic and nonmagnetic oscillators. This allows a determination of the higher-order multipole moments of rank 1 (dipole) to 6 (hexacontatetrapole). The strength of the Dy 4f multipole moments have been estimated as being up to 80% of the quadrupolar moment.(c) 2011 IOP Publishing LTD