Crystal and magnetic structure transitions in BiMnO3 d ceramics driven by cation vacancies and temperature

The crystal structure of BiMnO3 d ceramics has been studied as a function of nominal oxygen excess and temperature using synchrotron and neutron powder diffraction, magnetometry and differential scanning calorimetry. Increase in oxygen excess leads to the structural transformations from the monoclinic structure C2 c to another monoclinic P21 c , and then to the orthorhombic Pnma structure through the two phase regions. The sequence of the structural transformations is accompanied by a modification of the orbital ordering followed by its disruption. Modification of the orbital order leads to a rearrangement of the magnetic structure of the compounds from the long range ferromagnetic to a mixed magnetic state with antiferromagnetic clusters coexistent in a ferromagnetic matrix followed by a frustration of the long range magnetic order. Temperature increase causes the structural transition to the nonpolar orthorhombic phase regardless of the structural state at room temperature; the orbital order is destroyed in compounds BiMnO3 d d lt; 0.14 at temperatures above 470

Structural properties of Pb3Mn7O15 determined from high-resolution synchrotron powder diffraction

We report on the crystallographic structure of the layered compound Pb3Mn7O15. Previous analysis based on laboratory X-ray data at room temperature gave contradictory results in terms of the description of the unit cell. Motivated by recent magnetic bulk measurements of this system, we re-investigated the chemical structure with high-resolution synchrotron powder diffraction at temperatures between 15 K and 295 K. Our results show that the crystal structure of stoichiometric Pb3Mn7O15 has a pronounced 2-dimensional character and can be described in the orthorhombic space group Pnma.Comment: 6 pages, 4 figures, 2 table

Evolution of ( La 1 - y Pr y ) 0.7 Ca 0.3 MnO 3 crystal structure with A-cation size, temperature, and oxygen isotope substitution

PACS. 75.30.Vn Colossal magnetoresistance – 61.12.Ld Single-crystal and powder diffraction,

Magnetostructural relationship in the tetrahedral spin-chain oxide CsCoO2

We have investigated the structural and magnetic transitions in CsCoO2 using calorimetric measurements, neutron powder diffraction, density functional theory calculations, and muon-spin relaxation measurements. CsCoO2 exhibits three-dimensional long-range antiferromagnetic (AFM) order at 424 K, resulting in antiferromagnetic alignment of chains of ferromagnetically ordered Co-Co spin dimers. Although there is no change in magnetic structure around a structural transition at T∗=100 K, the resulting bifurcation of corner-shared Co-O-Co bond angles causes a weakening of the AFM interaction for one set of bonds along the chains. Consequently, the system undergoes a complex freezing out of relaxation processes on cooling