The emergence of magnetic ordering at complex oxide interfaces tuned by defects.

Complex oxides show extreme sensitivity to structural distortions and defects, and the intricate balance of competing interactions which emerge at atomically defined interfaces may give rise to unexpected physics. In the interfaces of non-magnetic complex oxides, one of the most intriguing properties is the emergence of magnetism which is sensitive to chemical defects. Particularly, it is unclear which defects are responsible for the emergent magnetic interfaces. Here, we show direct and clear experimental evidence, supported by theoretical explanation, that the B-site cation stoichiometry is crucial for the creation and control of magnetism at the interface between non-magnetic ABO3-perovskite oxides, LaAlO3 and SrTiO3. We find that consecutive defect formation, driven by atomic charge compensation, establishes the formation of robust perpendicular magnetic moments at the interface. Our observations propose a route to tune these emerging magnetoelectric structures, which are strongly coupled at the polar-nonpolar complex oxide interfaces.

Cr2Te3 Thin Films for Integration in Magnetic Topological Insulator Heterostructures.

Chromium telluride compounds are promising ferromagnets for proximity coupling to magnetic topological insulators (MTIs) of the Cr-doped (Bi,Sb)2(Se,Te)3 class of materials as they share the same elements, thus simplifying thin film growth, as well as due to their compatible crystal structure. Recently, it has been demonstrated that high quality (001)-oriented Cr2Te3 thin films with perpendicular magnetic anisotropy can be grown on c-plane sapphire substrate. Here, we present a magnetic and soft x-ray absorption spectroscopy study of the chemical and magnetic properties of Cr2Te3 thin films. X-ray magnetic circular dichroism (XMCD) measured at the Cr L2,3 edges gives information about the local electronic and magnetic structure of the Cr ions. We further demonstrate the overgrowth of Cr2Te3 (001) thin films by high-quality Cr-doped Sb2Te3 films. The magnetic properties of the layers have been characterized and our results provide a starting point for refining the physical models of the complex magnetic ordering in Cr2Te3 thin films, and their integration into advanced MTI heterostructures for quantum device applications.

Two-dimensional electron gases at LaAlO3/SrTiO3 interfaces: orbital symmetry and hierarchy engineered by crystal orientation.

Recent findings show the emergence of two-dimensional electron gases (2DEGs) at LaAlO(3)/SrTiO(3) interfaces along different orientations; yet details on band reconstructions have remained so far unknown. Via x-ray linear dichroism spectroscopy, we demonstrate that crystal symmetry imposes distinctive 2DEG orbital hierarchies on (001)-and (110)-oriented quantum wells, allowing selective occupancy of states of different symmetry. Such orientational tuning expands the possibilities for electronic engineering of 2DEGs and opens up enticing opportunities to understand the link between orbital symmetry and complex correlated states at LaAlO(3)/SrTiO(3) quantum wells.

Magnetic frustration, phase competition, and the magnetoelectric effect in NdFe3(BO3)4.

We present an element selective resonant magnetic x-ray scattering study of NdFe3(BO3)4 as a function of temperature and applied magnetic field. Our measurements show that the magnetic order of the Nd sublattice is induced by the Fe spin order. When a magnetic field is applied parallel to the hexagonal basal plane, the helicoidal spin order is suppressed and a collinear ordering, where the moments are forced to align in a direction perpendicular to the applied magnetic field, is stabilized. This result excludes a noncollinear spin order as the origin of the magnetically induced electric polarization in this compound. Instead our data imply that magnetic frustration results in a phase competition, which is the origin of the magnetoelectric response.

Femtoscale magnetically induced lattice distortions in multiferroic TbMnO3.

Magneto-electric multiferroics exemplified by TbMnO(3) possess both magnetic and ferroelectric long-range order. The magnetic order is mostly understood, whereas the nature of the ferroelectricity has remained more elusive. Competing models proposed to explain the ferroelectricity are associated respectively with charge transfer and ionic displacements. Exploiting the magneto-electric coupling, we used an electric field to produce a single magnetic domain state, and a magnetic field to induce ionic displacements. Under these conditions, interference between charge and magnetic x-ray scattering arose, encoding the amplitude and phase of the displacements. When combined with a theoretical analysis, our data allow us to resolve the ionic displacements at the femtoscale, and show that such displacements make a substantial contribution to the zero-field ferroelectric moment.

Orbital order at Mn and O sites and absence of Zener polaron formation in manganites.

We report the doping dependence of the ground state of A-site ordered manganites below and above half doping. Energy and polarization dependence of the orbital reflection, taken by resonant soft-x-ray powder diffraction, at both Mn L(2,3) and O K edges, provides direct evidence for orbital order at Mn(3+) and oxygen sites and absence of Zener polaron formation. For x > or = 0.2 anomalous melting of the orbital order is observed, which is coupled neither to magnetic ordering nor to a structural transition, indicating a two-dimensional character of the interactions.

Order-disorder nature of the antiferroelectric transition in Pb(2)MnWO(6).

The nature of the para-antiferroelectric phase transition in Pb(2)MnWO(6) was investigated by x-ray absorption spectroscopy. Extended x-ray absorption spectra (EXAFS) and x-ray absorption near-edge structure (XANES) at the Pb L(3)-edge, W L(3)-edge and Mn K-edge were measured at temperatures above and below the transition temperature, T(c)∼445 K. The temperature dependence of the local geometrical and electronic structure around each of the three atoms was quantitatively determined. XANES spectra confirm the expected formal valence state as Pb(2+), W(6+) and Mn(2+) both above and below T(c). There are no significant changes of the local structure around the three atoms, which remains distorted in the whole temperature range. This indicates the existence of dynamic local distortions with a short-range order in the paraelectric phase. Below T(c), the local distortions (and the electrical dipoles) are static and their ordered arrangement gives rise to the orthorhombic crystallographic structure. Above T(c), these distortions are dynamically disordered, causing an average cubic crystallographic structure. Hence, the phase transition is of the order-disorder type.

Probing and comparing electron doping and miss-site effects in Re-based double perovskites.

We have studied the Sr(2-x)La(x)Fe(1+x/2)Re(1-x/2)O(6) series in order to check how the increase in the number of Fe-O-Fe superexchange interactions affects the magnetic properties of this family of double perovskites. In these compounds the addition of La(3+) can be compensated by an increase of the Fe(3+) ratio leading to a non-electron-doped system. The unit cell of these samples expands on replacing Sr by La and the cationic ordering disappears for x>1 samples. Spontaneous magnetization at 5 K is observed in a wide range of concentrations but the magnetization at 5 T decreases as the La content increases. This result may be explained in terms of a ferrimagnetic ground state of the double perovskite. The magnetic ordering temperature increases with increasing the La and Fe content in agreement with an increase in the number of Fe-O-Fe interactions. The comparison to the electron-doped samples suggests that this effect is not enough to explain on its own the stronger T(C)-rise in Sr(2-x)La(x)FeReO(6) compounds.

The checkerboard pattern of Bi(0.63)Sr(0.37)MnO(3) determined using resonant x-ray scattering at the Mn K edge.

A study using resonant x-ray scattering at the Mn K edge has been carried out on a Bi(0.63)Sr(0.37)MnO(3) single crystal. This compound undergoes a metal-insulator phase transition to the so-called charge ordered (CO) state at about 530 K. Strong resonance signals were observed at room temperature as the energy was tuned through the Mn K edge for several superstructures of the CO phase. The energy, polarization and azimuth angle dependences agree with a checkerboard ordering in the ab plane of manganese atoms of two types, in terms of their different local geometrical structures. One of the sites is anisotropic-a tetragonal distorted oxygen octahedron-and the other is isotropic-a nearly undistorted one, as observed for Bi(0.5)Sr(0.5)MnO(3) and other half-doped manganites. This result indicates that the checkerboard pattern is strongly stable and extends to doping concentrations x<0.5. No superstructures corresponding to the doubling of the c axis were detected. Intermediate valence states lower than 3.5, according to the fractional charge segregation, were deduced for the two non-equivalent Mn atoms, i.e. Mn(3.30+) and Mn(3.44+).

[Prevalence of psychiatric pathology at a rural health centre]. / Prevalencia de psicopatías en un centro de salud rural.

OBJECTIVES: To find the prevalence of psychiatric pathology at a rural health centre and to compare the results with results from studies with a similar design. DESIGN: Two-stage crossover study of prevalence: first, detection and then, psychiatric pathology evaluation.Setting. El Marquesado Health Centre (Granada). Scattered rural population with low social and economic level and high percentage of elderly people. PARTICIPANTS: Simple randomised sample representing the population over 18. N=245; error alpha=5%. Sampling source: electoral register. MEASUREMENTS: GHQ-28 Goldberg Questionnaire, social and demographic data, and CAGE test. The CIS questionnaire for psychiatry was administered to those who exceeded the cut-off point (GHQ-28=5) and they were allocated a DSM IV diagnosis. If CAGE was>=2, damaging alcohol consumption was studied. If there was a prior diagnosis, the second stage was avoided. Measurements of prevalence with their exact confidence intervals were made. RESULTS: Prevalence of psychiatric pathology: 28.6% (34.5% in women and 22.6% in men). 30% of cases had two diagnoses. Anxiety disorders were the most common pathology (8.97%), representing 23.9% of the grouped diagnoses. Depression disorders had 8.16% prevalence; problematic consumption of substances, 6.12%. The most common isolated diagnosis was Dysthymia (9.78% of cases). Hidden psychiatric morbidity reached 40%. CONCLUSIONS: The prevalence of psychiatric pathology is very high. The most common disorders are those of anxiety, followed by depression and damaging alcohol consumption.