Magnetic ground state and multiferroicity in BiMnO3_3

We argue that the centrosymmetric $C2/c$ symmetry in BiMnO$_3$ is spontaneously broken by antiferromagnetic (AFM) interactions existing in the system. The true symmetry is expected to be $Cc$, which is compatible with the noncollinear magnetic ground state, where the ferromagnetic order along one crystallographic axis coexists with the the hidden AFM order and related to it ferroelectric polarization along two other axes. The $C2/c$ symmetry can be restored by the magnetic field $B \sim 35$ Tesla, which switches off the ferroelectric polarization. Our analysis is based on the solution of the low-energy model constructed for the 3d-bands of BiMnO$_3$, where all the parameters have been derived from the first-principles calculations. Test calculations for isostructural BiCrO$_3$ reveal an excellent agreement with experimental data.Comment: 5 pages, 5 figure

Pbca-Type In2O3: the high-pressure post-corundum phase at room temperature

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Journal of Physical Chemistry C, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://dx.doi.org/10.1021/jp5061599High-pressure powder X-ray diffraction and Raman scattering measurements in cubic bixbyite-type indium oxide (c-In2O3) have been performed at room temperature. On increasing pressure c-In2O3 undergoes a transition to the Rh2O3-II structure but on decreasing pressure Rh2O3-II-type In2O3 undergoes a transition to a previously unknown phase with Pbca space group which is isostructural to Rh2O3-III. On further decrease of pressure, we observed a phase transition to the metastable corundum-type In2O3 near room conditions. Recompression of the metastable corundum-type In2O3 at room temperature leads to a transition to the Rh2O3-III phase, thus showing that the Rh2O3-III phase is the post-corundum phase at room temperature. Our results are supported by theoretical ab initio calculations. Furthermore, they show that the Rh2O3-III phase could be present in other sesquioxides, thus prompting to a revision of the pressure-temperature phase diagrams of sesquioxidesFinancial support by the Spanish MEC under Grant No. MAT2010-21270-C04-01/03/04, MAT2013-46649-C4-1/2/3-P, by MALTA Consolider Ingenio 2010 project (CSD2007-00045) and by Generalitat Valenciana (GVA-ACOMP-2013-012). Red Espanola de Supercomputacion (RES) and ALBA Synchrotron Light Source are also acknowledged. B.G.-D. and J.A.S. acknowledge financial support through the FPI program and Juan de la Cierva fellowship, respectively. We also thank J. L. Jorda for fruitful discussions. A.L.J.P. acknowledges financial support through Brazilian CNPq. A.S. expresses thanks to FEDER Grant UNLV10-3E-1253 for financial support.García-Domene, B.; Sans Tresserras, JÁ.; Gomis, O.; Manjón Herrera, FJ.; Ortiz, HM.; Errandonea, D.; Santamaría Pérez, D.... (2014). Pbca-Type In2O3: the high-pressure post-corundum phase at room temperature. Journal of Physical Chemistry C. 118(35):20545-20552. https://doi.org/10.1021/jp5061599S20545205521183

Ag injection to Bi2_{2}Sr2_{2}CaCu2_{2}Oy_y superconductor by shock-loading

The platelet bulk specimen Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{\rm y}$ sandwiched between Ag disks was shocked to 5 GPa using shock loading method. The shocked specimen showed high orientation to c-axis and consolidation of high density of 95 %. Ag particles of about 10 nm were observed on the surface of Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{\rm y}$ specimen by TEM. The magnetization of zero field cooling strongly increased and $T_{c}$ reached to 8 4 K from 74 K by the annealing at 650 $^{\circ}$C for 12 hs in N$_{2}$ after shock loading. The $\Delta$M (the difference of FC and ZFC) was enhanced about 50 times than pristine specimen. The introduction of pinning site was discussed in connection with jetting effects of shock wave

Phase stability and elasticity of Sc 2O 3 at high pressure

An investigation into the high-pressure behavior of Sc2O3 was conducted using first-principle calculations based on density functional theory within the generalized gradient approximation. Nine candidate phases were considered and simulated, C-, B-, A-RES, Rh2O3(II), Gd2S3, U2S3, Al2Er3, corundum and PPv respectively. Our results demonstrate phase transitions of Sc2O3 from C- to B-RES phase at 15 GPa, then to Gd2S3 phase at 18 GPa. Elastic constants of Sc2O3 present softening from about 270 GPa to 337 GPa, associated with a semiconductor-to-metal crossover. The Gd2S3-type Sc2O3 is both mechanically and dynamical stable at least up to 302 GPa supported by the mechanically stable criteria and the phonon spectrum

Orbital ordering as the determinant for ferromagnetism in biferroic BiMnO<SUB>3</SUB>

The ferromagnetic structure of BiMnO3, Tc=105 K, has been determined from powder neutron-diffraction data collected at 20 K on a sample synthesized at high pressures using a cubic anvil press. BiMnO3 is a distorted perovskite that crystallizes in the monoclinic space group C2 with unit-cell parameters a=9.5317(7) Å, b=5.6047(4) Å, c=9.8492(7) Å, and β=110.60(1)° (Rp=6.78%, wRp=8.53%, reduced χ2=1.107). Data analysis reveals a collinear ferromagnetic structure with the spin direction along [010] and a magnetic moment of 3.2μB. There is no crystallographic phase transition on cooling the polar room-temperature structure to 20 K, lending support to the belief that ferromagnetism and ferroelectricity coexist in BiMnO3. Careful examination of the six unique Mn-O-Mn superexchange pathways between the three crystallographically independent Mn3+ sites shows that four are ferromagnetic and two are antiferromagnetic, thereby confirming that the ferromagnetism of BiMnO3 stems directly from orbital ordering