Spin and Orbital Ordering Transitions in RVO3 compounds : new insights from diffraction studies on TmVO3

Orateur : Clemens RITTER (ILL Grenoble)

Overshadowed for a long time by the isostructural colossal magnetoresistive manganites the family of rare earth vanadates RVO3 have gained strong interest in the last 10-15 years due to their highly interesting interplay of orbital and spin ordering transitions. The relatively weak Jahn-Teller effect of the 3d2 electron system of V3+ ions induces in these Mott insulators orbital orderings at temperatures not too distant from the spin ordering temperatures. The presence of orbital fluctuations has been put forward for the triply degenerate t2g orbitals and for YVO3 even the formation of an orbital Peirls state has been proposed. Dependent on the rare earth ion radius and the temperature the combination of GeFeO3-type distortion, orbital order, R-O hybridisation and V3+, R3+ spin order leads to a fascinating phase diagram of the RVO3 series. Still rare are, however, studies of the temperature dependent structural and magnetic details using diffraction methods. Trying to counter this situation an extensive study using high resolution and high intensity neutron and synchrotron powder diffraction was undertaken on TmVO3 in order to clarify the part of the phase diagram of the RVO3 series where the ionic radius of R3+ is relatively small. A fascinating plethora of phenomena including structural and magnetic phase coexistences, orbital order flipping and spontaneous spin flop transition will be presented and put into the general context of the physics of the vanadates RVO3.

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