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V-doped (Bi,Sb)2Te3 has a ten times higher magnetic coercivity than its Cr-doped counterpart and, therefore, is believed to be advantageous for the quantum anomalous Hall effect (QAHE). The QAHE requires the opening of a magnetic bandgap at the Dirac point. We do not find this gap by angle-resolved photoelectron spectroscopy down to 1 K. By x-ray magnetic circular dichroism (XMCD), we directly probe the magnetism at the V site and derive spin and orbital magnetic moments of 1.69 and –0.22 μ B /atom. Hysteresis curves of the XMCD signal show a strong dependence of the coercivity on the ramping velocity of the magnetic field. The XMCD signal decays on a timescale of minutes, which we conclude contributes to the absence of a detectable magnetic gap at the Dirac point. [ABSTRACT FROM AUTHOR]

We used fs- and ps- resonant magnetic x-ray diffraction to probe the laser-induced changes to the magnetic profile in thin films of the antiferromagnetic semicon-ductor EuTe.

We present resonant soft x-ray scattering studies of Ti 3d and O 2p states at the interfaces of SrTiO3/LaAlO3 superlattices. From reflectivity analyses, focusing on the (003) peak which is forbidden for our “ideal” superlattice structure, we concluded that the LaO|TiO2/SrO and the SrO|AlO2/LaO interfaces have distinct reconstructions, breaking the heterostructure symmetry. [ABSTRACT FROM AUTHOR]

Resonant soft x-ray scattering studies of Ti 3d and O 2p states at the interfaces of SrTi[O.sub.3]/LaAl[O.sub.3] superlattices are described. Reflectivity analyses have shown that the LaO/Ti[O.sub.2]/SrO and the SrO/Al[O.sub.2]/LaO interfaces have distinct reconstructions, breaking the heterostructure symmetry.

We report on resonant magnetic x-ray scattering and absorption spectroscopy studies of exchange-coupled antiferromagnetic ordering of Eu3+ magnetic moments in multiferroic Eu1-xYxMnO3 in the absence of an external magnetic field. The observed resonant spectrum is characteristic of a magnetically ordered 7 F1 state that mirrors the Mn magnetic ordering, due to exchange coupling between the Eu 4f and Mn 3d spins. Here, we observe long-range magnetic order generated by exchange coupling of magnetic moments of formally nonmagnetic Van Vleck ions, which is a step further towards the realization of exotic phases induced by exchange coupling in systems entirely composed of non magnetic ions. [ABSTRACT FROM AUTHOR]

The structural and magnetic properties of (Fe/Si) nanostructures obtained by successive deposition on the SiO/Si(100) surface at a temperature of the substrate of 300 K have been studied. The thicknesses of all Fe and Si layers have been determined by transmission electron microscopy measurements. The magnetic properties have been studied by the X-ray magnetic circular dichroism (XMCD) method near the Fe L absorption edges. The orbital ( m) and spin ( m) contributions to the total magnetic moment of iron have been separated. The thicknesses of magnetic and nonmagnetic iron silicide on the Si/Fe and Fe/Si interfaces have been determined with the surface sensitivity of the XMCD method and the model of the interface between the nonmagnetic and weakened magnetic phases. [ABSTRACT FROM AUTHOR]

We have used resonant x-ray diffraction to develop a detailed description of antiferromagnetic ordering in epitaxial superlattices based on two-unit-cell thick layers of the strongly correlated metal LaNiO3. We also report reference experiments on thin films of PrNiO3 and NdNiO3. The resulting data indicate a spiral state whose polarization plane can be controlled by adjusting the Ni d-orbital occupation via two independent mechanisms: epitaxial strain and spatial confinement of the valence electrons. The data are discussed in light of recent theoretical predictions. [ABSTRACT FROM AUTHOR]

Resonant (elastic) soft x-ray scattering (RSXS) offers a unique element, site and valence specific probe to study spatial modulations of charge, spin and orbital degrees of freedom in solids on the nanoscopic length scale. It is not only used to investigate single-crystalline materials. This method also enables one to examine electronic ordering phenomena in thin films and to zoom into electronic properties emerging at buried interfaces in artificial heterostructures. During the last 20 years, this technique, which combines x-ray scattering with x-ray absorption spectroscopy, has developed into a powerful probe to study electronic ordering phenomena in complex materials and furthermore delivers important information on the electronic structure of condensed matter. This review provides an introduction to the technique, covers the progress in experimental equipment, and gives a survey on recent RSXS studies of ordering in correlated electron systems and at interfaces. [ABSTRACT FROM AUTHOR]

Femtosecond (fs) soft x-ray diffraction at the Eu-M5 resonance was employed to study the dynamics of antiferromagnetic (AFM) order in a thin film of the magnetic semiconductor EuTe after fs laser excitation. The AFM Bragg peak intensity displays an ultrafast decay with an upper limit for the time constant of (700±200) fs followed by fast recovery with (47±10) ps. Reciprocal space scans across the diffraction peak could be recorded with picosecond and fs time resolution, demonstrating that even at synchrotron slicing sources ultrafast studies of spatial magnetic correlations are feasible. The results show that fs dynamics of materials with complex order parameters can be addressed. [ABSTRACT FROM AUTHOR]

We employ the strong variation of the photon penetration depth across an electronic resonance in soft x-ray scattering for a depth resolved study of an antiferromagnetic (AFM) thin film. We directly observed the development of the helical AFM structure in thin Dy(001) films on W(110) across the temperature-induced phase transition from ferromagnetic to helical AFM order. [ABSTRACT FROM AUTHOR]

Incommensurate charge order (CO) has been identified as the leading competitor of high-temperature superconductivity in all major families of layered copper oxides, but the perplexing variety of CO states in different cuprates has confounded investigations of its impact on the transport and thermodynamic properties. The three-dimensional (3D) CO observed in YBa2Cu3O6+x in high magnetic fields is of particular interest, because quantum transport measurements have revealed detailed information about the corresponding Fermi surface. Here we use resonant X-ray scattering to demonstrate 3D-CO in underdoped YBa2Cu3O6+x films grown epitaxially on SrTiO3 in the absence of magnetic fields. The resonance profiles indicate that Cu sites in the charge-reservoir layers participate in the CO state, and thus efficiently transmit CO correlations between adjacent CuO2 bilayer units. The results offer fresh perspectives for experiments elucidating the influence of 3D-CO on the electronic properties of cuprates without the need to apply high magnetic fields. In many cuprates the high temperature superconducting state competes with a charge ordered phase that has been difficult to investigate in detail. Here the authors show three-dimensional charge order can be stabilized in YBCO films and studied without using the high magnetic fields that are necessary in the bulk material. [ABSTRACT FROM AUTHOR]

We present results on the magnetic field dependence of the stripe order in La1.64Eu0.2Sr0.16CuO4 (LESCO). Using resonant soft x-ray scattering at the oxygen K edge to probe the (0.259,0,0.648) superlattice reflection, which is commonly associated to charge stripes, we found no pronounced difference in the wave vector, peak widths, and integrated intensity for magnetic fields up to B=6 T. This is in strong contrast to the behavior observed for La1.875Sr0.125CuO4, where a stabilization of the charge modulation in high magnetic fields has been demonstrated. [ABSTRACT FROM AUTHOR]

We report the results of a comprehensive study of charge-density wave (CDW) correlations in untwinned YBa2Cu3O6+x single crystals with 0.4 ⩽ x ⩽ 0.99 using Cu L3 edge resonant x-ray scattering (RXS). Evidence of CDW formation is found for 0.45 ⩽ x ⩽ 0.93 (hole-doping levels 0.086 ≲ p ≲ 0.163), but not for samples with x ⩽ 0.44 (p ≲ 0.084) that exhibit incommensurate spin-density-wave order, and in slightly overdoped samples with x = 0.99 (p ∼ 0.19). This suggests the presence of two proximate zero-temperature CDW critical points at Pc1 ∼ 0.08 and pc2 ∼ 0.18. Remarkably, pc2 is close to the doping level that is optimal for superconductivity. The CDW reflections are observed at incommensurate in-plane wave vectors (δa, 0) and (0, δb) with δa < δa. Both δa and δb decrease linearly with increasing doping, in agreement with recent reports on Bi-based high-Tc; superconductors, but in sharp contrast to the behavior of the La2-x (Ba,Sr)xCuO4 family. The CDW intensity and correlation length exhibit maxima at p ∼ 0.12, coincident with a plateau in the superconducting transition temperature Tc. The onset temperature of the CDW reflections depends nonmonotonically on p , with a maximum of ∼160 K for p ∼ 0.12. The RXS reflections exhibit a uniaxial intensity anisotropy. Whereas in strongly underdoped samples the reflections at (δa, 0) are much weaker than those at (0, δb), the anisotropy is minimal for p ∼ 0.12, and reversed close to optimal doping. We further observe a depression of CDW correlations upon cooling below Tc, and (for samples with p ⩾ 0.09) an enhancement of the signal when an external magnetic field up to 6 T is applied in the superconducting state. For samples with p ∼ 0.08, where prior work has revealed a field-enhancement of incommensurate magnetic order, the RXS signal is field independent. This supports a previously suggested scenario in which incommensurate charge and spin orders compete against each other, in addition to individually competing against superconductivity [Blanco-Canosa et al., Phys. Rev. Lett. 110, 187001 (2013)]. We discuss the relationship of these results to prior observations of "stripe" order in La2-x(Ba,Sr)xCuO4 , the "pseudogap" phenomenon, superconducting fluctuations, and quantum oscillations, as well as their implications for the mechanism of high-temperature superconductivity. [ABSTRACT FROM AUTHOR]

Abstract: Magnetic soft X-ray scattering at the Ho M5 resonance was characterized using thin films, thus reducing the effect of the strong photon absorption. Magnetic scattering factors are found to be as large as at resonance, while the effective probing depth of the X-rays at the resonance maximum is of the order of 30Å at . The huge enhancement of magnetic scattering allows one to study ultrathin Ho films, which is exploited to investigate the thickness dependence of the Néel temperature in these long-period antiferromagnets. The tunable X-ray penetration depth across the resonance can be used for magnetic depth profiling, e.g. to study the depth-dependent growth of antiferromagnetic domains across the ferromagnetic/antiferromagnetic phase transition in Dy metal films. [Copyright &y& Elsevier]

V-doped (Bi,Sb)2Te3 has a ten times higher magnetic coercivity than its Cr-doped counterpart and, therefore, is believed to be advantageous for the quantum anomalous Hall effect (QAHE). The QAHE requires the opening of a magnetic bandgap at the Dirac point. We do not find this gap by angle-resolved photoelectron spectroscopy down to 1 K. By x-ray magnetic circular dichroism (XMCD), we directly probe the magnetism at the V site and derive spin and orbital magnetic moments of 1.69 and –0.22 μ B /atom. Hysteresis curves of the XMCD signal show a strong dependence of the coercivity on the ramping velocity of the magnetic field. The XMCD signal decays on a timescale of minutes, which we conclude contributes to the absence of a detectable magnetic gap at the Dirac point. [ABSTRACT FROM AUTHOR]

Resonant x-ray scattering at the Dy M5 and Ni L3 absorption edges was used to probe the temperature and magnetic field dependence of magnetic order in epitaxial LaNiO3-DyScO3 superlattices. For superlattices with 2 unit cell thick LaNiO3 layers, a commensurate spiral state develops in the Ni spin system below 100 K. Upon cooling below Tind=18 K, Dy-Ni exchange interactions across the LaNiO3-DyScO3 interfaces induce collinear magnetic order of interfacial Dy moments as well as a reorientation of the Ni spins to a direction dictated by the strong magnetocrystalline anisotropy of Dy. This transition is reversible by an external magnetic field of 3 T. Tailored exchange interactions between rare-earth and transition-metal ions thus open up new perspectives for the manipulation of spin structures in metal-oxide heterostructures and devices. [ABSTRACT FROM AUTHOR]

Using resonant soft-x-ray scattering as a function of both temperature and magnetic field, we reveal a large number of almost degenerate magnetic orders in SrCo6O11. The Ising-like spins in this frustrated material in fact exhibit a so-called magnetic devil's staircase. It is demonstrated how a magnetic field induces transitions between different microscopic spin configurations, which is responsible for the magnetoresistance of SrCo6O11. This material therefore constitutes a unique combination of a magnetic devil's staircase and spin-valve effects, yielding a novel type of magnetoresistance system. [ABSTRACT FROM AUTHOR]

The magnetic anisotropy of TbMnO3 was explored by means of polarized x-ray absorption spectroscopy and x-ray magnetic circular dichroism (XMCD) measurements at the MnL2,3 and TbM4,5 edges as a function of temperature and magnetic-field intensity. The selective magnetometry measurements were compared with the macroscopic magnetic properties on single crystals. XMCD measurements at the TbM4,5 edge as a function of the magnetic field reproduces quite well the macroscopic magnetic anisotropy at low temperatures with the Tb moments staying confined along their Ising axis within the ab plane, whereas a weak XMCD signal is observed at the MnL2,3 edge. These results point out that Tb3+ single-ion anisotropy is the only responsible for the magnetic anisotropy on this multiferroic compound at high magnetic fields. Moreover, we found MnL2,3 XMCD measurements show that the cycloidal antiferromagnetic order is almost unaffected by the applied magnetic field at low temperatures under an applied magnetic field. Therefore, we discuss that this strong Ising nature of Tb3+ ions, through a magnetocrystalline coupling mediated by the oxygen atoms, must play an important role in the field-induced electric polarization flop and therefore in the magnetoelectric coupling on TbMnO3. [ABSTRACT FROM AUTHOR]

We use polarized Raman scattering to probe lattice vibrations and charge ordering in 12 nm thick, epitaxially strained PrNiO3 films, and in superlattices of PrNiO3 with the band insulator PrAlO3. A carefully adjusted confocal geometry is used to eliminate the substrate contribution to the Raman spectra. In films and superlattices under tensile strain which undergo a metal-insulator transition upon cooling, the Raman spectra reveal phonon modes characteristic of charge ordering. These anomalous phonons do not appear in compressively strained films, which remain metallic at all temperatures. For superlattices under compressive strain, the Raman spectra show no evidence of anomalous phonons indicative of charge ordering, while complementary resonant x-ray scattering experiments reveal antiferromagnetic order associated with a modest increase in resistivity upon cooling. This confirms theoretical predictions of a spin density wave phase driven by spatial confinement of the conduction electrons. [ABSTRACT FROM AUTHOR]

We use resonant x-ray scattering to determine the momentum-dependent charge correlations in YBa2Cu3O6.55 samples with highly ordered chain arrays of oxygen acceptors (ortho-H structure). The results reveal nearly critical, biaxial charge density wave (CDW) correlations at in-plane wave vectors (0.315, 0) and (0, 0.325). The corresponding scattering intensity exhibits a strong uniaxial anisotropy. The CDW amplitude and correlation length are enhanced as superconductivity is weakened by an external magnetic field. Analogous experiments are carried out on a YBa2Cu3O6.6 crystal with a dilute concentration of spinless (Zn) impurities, which had earlier been shown to nucleate incommensurate magnetic order. Compared to pristine crystals with the same doping level, the CDW amplitude and correlation length are found to be strongly reduced. These results indicate a three-phase competition between spin-modulated, charge-modulated, and superconducting states in underdoped YBa2Cu3O6+δ. [ABSTRACT FROM AUTHOR]

Here we present linear-polarization-dependent soft x-ray absorption spectroscopy data at the Ce M4,5 edges of CeOs2Al10 and CeFe2Al10. Despite the strong hybridization between 4f and conduction electrons and the existence of spin gaps as seen in inelastic neutron scattering, we were able to determine the crystal field ground state wave functions by combining our spectroscopy data with magnetization measurements. The results quantitatively explain the small ordered moment along c and the measured magnetic moment along the easy a axis in CeOs2Al10. [ABSTRACT FROM AUTHOR]

The concept that superconductivity competes with other orders in cuprate superconductors has become increasingly apparent, but obtaining direct evidence with bulk-sensitive probes is challenging. We have used resonant: soft x-ray scattering to identify two-dimensinnal charge fluctuations with an incommensurate periodicity of ~3.2 lattice units in the copper-oxide planes of the superconductors (Y, Nd)Ba2Cu3O6+x, with hole concentrations of 0.09 to 0.13per planar Cu ion. The intensity and correlation length of the fluctuation signal increase strongly upon cooling down to the superconducting transition temperature (Tc); further cooling below Tc abruptly reverses the divergence of the charge correlations. In combination with earlier observations of a large gap in the spin excitation spectrum, these data indicate an incipient charge density wave instability that competes with superconductivity. [ABSTRACT FROM AUTHOR]

We studied the symmetry of the Fe 3d wave function in magnetite below the Verwey temperature Tv with resonant soft-x-ray diffraction. Although the lattice structure of the low-temperature phase of Fe3O4 is well described by the pseudo-orthorhombic Pmca with a slight monoclinic P2/c distortion, we find that the 3d wave function does not reflect the Pmca symmetry, and its distortion toward monoclinic symmetry is by far larger than that of the lattice. The result supports a scenario in which the Verwey transition involves the ordering of t2f, orbitals with complex-number coefficients. [ABSTRACT FROM AUTHOR]

We report combined soft and hard x-ray scattering studies of the electronic and lattice modulations associated with stripe order in La1.875Ba0.125CuO4 and La1.48Nd0.4Sr0.12CuO4. We find that the amplitude of both the electronic modulation of the hole density and the strain modulation of the lattice is significantly larger in La1.875Ba0.125CuO4 than in La1.48Nd0.4Sr0.12CuO4 and is also better correlated. The in-plane correlation lengths are isotropic in each case; for La1.875Ba0.125CuO4, ξhole = 255 + 5 Å, whereas for La1.48Nd0.4Sr0.12CuO4, ξhole = 111 ± 7 Å. We find that the modulations are temperature independent in La1.875Ba0.125CuO4 in the low temperature tetragonal phase. In contrast, in La1.48Nd0.4Sr0.12CuO4, the amplitude grows smoothly from zero, beginning 13 K below the LTT phase transition. We speculate that the reduced average tilt angle in La1.875Ba0.125CuO4 results in reduced charge localization and incoherent pinning, leading to the longer correlation length and enhanced periodic modulation amplitude. [ABSTRACT FROM AUTHOR]

We studied the (00½) diffraction peak in the low-temperature phase of magnetite (Fe3O4) using resonant soft x-ray diffraction at the Fe-L2,3 and O-K resonances. We studied both molecular-beam-epitaxy grown thin films and in situ cleaved single crystals. From the comparison, we have been able to determine quantitatively the contribution of intrinsic absorption effects, thereby arriving at a consistent result for the (00½) diffraction peak spectrum. Our data also allow for the identification of extrinsic effects, e.g., for a detailed modeling of the spectra in case a dead surface layer is present that is only absorbing photons but does not contribute to the scattering signal. [ABSTRACT FROM AUTHOR]

The understanding of the origin of superconductivity in cuprates has been hindered by the apparent diversity of intertwining electronic orders in these materials. We combined resonant x-ray scattering (REXS), scanning-tunneling microscopy (STM), and angle-resolved photoemission spectroscopy (ARPES) to observe a charge order that appears consistently in surface and bulk, and in momentum and real space within one cuprate family, Bi2Sr2-LaxCu06+δ. The observed wave vectors rule out simple antinodal nesting in the single-particle limit but match well with a phenomenological model of a many-body instability of the Fermi arcs. Combined with earlier observations of electronic order in other cuprate families, these findings suggest the existence of a generic charge-ordered state in underdoped cuprates and uncover its intimate connection to the pseudogap regime. [ABSTRACT FROM AUTHOR]