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Spin and orbital orderings are amongst the most important phenomena in the solid state chemistry of oxides. Physical property and powder neutron and X-ray diffraction measurements are reported for a range of mostly low dimensional ternary transition metal oxides which display spin or orbital order. Extensive studies of the physical properties and crystal structure of In2VO5 are reported. The structure of this material consists of one dimensional zig-zag chains of orbitally ordered S = 1/2 V4+. Magnetic susceptibility measurements show an unusual crossover from dominant ferromagnetic (θ = 17 K) to antiferromagnetic (θ = -70 K) exchange at 120 K, which is attributed to ferromagnetic dimerisation driven by magnetic frustration. The magnetic moment also increases from 1.81 to 2.2μB at the 120 K crossover. Heat capacity measurements confirm this scenario as the magnetic entropy tends towards 1/2 Rln3 below 120 K before approximating to Rln2 at high temperature. Synchrotron x-ray diffraction and high resolution neutron powder diffraction show no bulk structural changes, but the b axis, along which the VO6 chains run, shows an anomalous expansion below 120 K. At low temperatures, a downturn in the magnetic susceptibility is seen at 2.5 K, signifying a spin freezing transition. Heat capacity and powder neutron diffraction measurements show no evidence for long range magnetic order down to 0.42 K. The low dimensional brannerite materials MV2O6 (M = Mn, Co, Ni) were synthesised by a sol-gel method. Magnetic properties were investigated by magnetisation, powder neutron diffraction and in the case of CoV2O6, heat capacity measurements. The structure of these materials consists of linear chains of edge sharing MO6 octahedra. Monoclinic MnV2O6 is an isotropic antiferromagnet with TN = 20 K and a reduced magnetic coherence length due to 3 % Mn/V antisite disorder. The magnetic structure consists of ferromagnetic edge-sharing chains with k = (0,0,1/2) and a refined Mn moment of 4.77(7) μB. The triclinic materials CoV2O6 and NiV2O6 are also antiferromagnetic with TN = 7 and 14 K respectively and both show metamagnetic type transitions. Unusually, M(H) isotherms recorded below 5 K for CoV2O6 show a plateau at 1/3 of the saturation magnetisation. This feature, together with a long period modulated magnetic structure, is attributed to strong single ion (Ising) type anisotropy and nearest neighbour ferromagnetic exchange. Preliminary high pressure experiments on NiV2O6 have confirmed a previously reported transition to a columbite phase at 6 GPa and 900 °C. The high pressure polymorph is also antiferromagnetic with TN = 2.5 K. The previously uncharacterised perovskite, PbRuO3 has been prepared using high pressure/temperature synthesis techniques (10 GPa, 1000 °C). Synchrotron powder X-ray diffraction measurements show that the room temperature structure is orthorhombic, Pnma. A first order orbital ordering transition occurs at 75 K with an associated metal insulator transition. Below 75 K, the dxz orbitals are preferentially occupied and the structure is orthorhombic Imma. The transition may be driven by an increase in antiferroelectric Pb2+ displacements, whcih reach a peak at ~ 125 K. A further structural transition to a larger monoclinic cell is also identified at 9.7 K. The physical properties and crystal structures of two low dimensional lead manganese oxides have also been investigated. Acentric Pb2MnO4, which has a structure consisting of edge sharing chains, is antiferromagnetic with TN = 18 K. Powder neutron diffraction shows the magnetic structure consists of antiferromagnetic chains with k = (0,0,0) and a refined Mn moment of 2.74(2) μB. The crystal point group allows piezoelectricity and the magnetic point group symmetry allows piezomagnetism. We speculate that coupled magnetic and electric properties may be observed in this material. The layered material, Pb3Mn7O15, with a structure consisting of 1/2 filled Kagomé layers has also been studied. Single crystals were prepared by a flux growth method and polycrystalline material was prepared by the ceramic method. Powder neutron and synchrotron x-ray diffraction studies show that the single crystals are hexagonal and that the polycrystalline material is orthorhombic. Furthermore, heat capacity measurements show that the hexagonal single crystal material undergoes a glassy magnetic transition. In contrast, powder neutron diffraction shows that the orthorhombic polycrystalline material has coherent long range magnetic order. These differences are attributed to an oxygen deficiency in the polycrystalline magnetic order. These differences are attributed to an oxygen deficiency in the polycrystalline material.

The magnetic structures and spin reorientations of RGa (R = Gd, Dy, Ho and Er) intermetallic compounds have been investigated using neutron powder diffraction and rare earth Mössbauer spectroscopy. The aim has been to determine the magnetic structures of these compounds before and after their spin reorientation transitions and to understand the role of the crystal field and exchange interactions in the spin reorientation mechanism. The results have been compared with those found from previous single-crystal susceptibility measurements on RGa and the recent 119Sn Mössbauer spectroscopy work on Sn-doped RGa compounds. The magnetic structures obtained at low temperatures are a simple collinear ferromagnetic in DyGa, canted ferromagnetic in HoGa and a non-collinear ferromagnetic in GdGa. The spin reorientation in ErGa was also observed by 166Er Mössbauer spectroscopy. These results show that both the crystal field and exchange interactions play an important role in the reorientation mechanism.

The magnetic structures and spin reorientations of RGa (R = Gd, Dy, Ho and Er) intermetallic compounds have been investigated using neutron powder diffraction and rare earth Mössbauer spectroscopy. The aim has been to determine the magnetic structures of these compounds before and after their spin reorientation transitions and to understand the role of the crystal field and exchange interactions in the spin reorientation mechanism. The results have been compared with those found from previous single-crystal susceptibility measurements on RGa and the recent 119Sn Mössbauer spectroscopy work on Sn-doped RGa compounds. The magnetic structures obtained at low temperatures are a simple collinear ferromagnetic in DyGa, canted ferromagnetic in HoGa and a non-collinear ferromagnetic in GdGa. The spin reorientation in ErGa was also observed by 166Er Mössbauer spectroscopy. These results show that both the crystal field and exchange interactions play an important role in the reorientation mechanism.

Thesis (M.S.)--University of Wisconsin--Madison, 1953. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

<p> Magnetic susceptibility data indicate that Tb2Mo2O7 undergoes a spin glass transition at 25 K. The crystal structure is consistent with the fully ordered pyrochlore model. Short range order, involving ferromagnetic and antiferromagnetic correlations, is observed down to 8 K by neutron scattering. </p> <p> Sr2Cr03F and SrLaCr04 have the same magnetic structure. The neutron diffraction data are consistent with two different models. In both cases the magnetic cell is √2a and c and the magnetic moments lie out of the plane. However, in one model the in-plane projection is canted and in the other it is colinear. Sr2Cr03F has a Tc value of 132(2) K and a susceptibility maximum at 280 K. SrLaCr04 has a Tc value of approximately 200 K and a susceptibility maximum near 400 K. The critical· exponent β for Sr2Cr03F is 0.26(4). The (100) magnetic reflection of both SrLaCr04 and Sr2Cr03F shows short range order correlations above Tc. </p> / Thesis / Master of Science (MSc)

Thesis (Ph. D.)--University of Missouri-Columbia, 1998. / Typescript. Vita. Includes bibliographical references (leaves 179-190). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1998. / Typescript. Vita. Includes bibliographical references (leaves 179-190). Also available on the Internet.

Magnetic Structure of antiferromagnetic Mn₂P₂O₇ at 4.2º K has been established by neutron diffraction from a powder specimen. The magnetic unit cell is found to be the same size as the chemical unit cell. The spins are arranged in ferromagnetic sheets with the moments in each sheet aligned antiferromagnetically relative to its adjacent sheets. Neutron diffraction results in regard to the critical temperature (13±3)º K, and the spine being at an angle of 23º from the a-axis in the a-c plane have been found consistent with the ones obtained by Fowlis, Atkinson, Choh and Stager by susceptibility and NMR studies on the material. However, to confirm the angle with some precision, more work, probably with a single crystal, will be required. / Thesis / Master of Science (MSc)

<p> The magnetic structures of antiferromagnetic manganese pyrophosphate and copper pyrophosphate have been determined by single crystal neutron diffraction techniques. More detailed features of the magnetic structure have been determined by nuclear magnetic resonance (NMR). A discrepancy between previous NMR measurements on Mn2P2o7 and the single crystal neutron measurements was resolved by postulating a low temperature crystallographic phase transition. Information about the dependence of the transferred hyperfine interaction upon the separation of the relevant ions is obtained for Cu2P2o7 from the NMR data and from previously determined deviations from a higher symmetry phase. The origin of the magnetic anisotropy energy in Cu2P2o7 is discussed. </p> / Thesis / Doctor of Philosophy (PhD)