A cobaltite with a room temperature electrical and magnetic transition: YBaCo4O7

The physical properties of an oxygen stoichiometric sample, YBaCo4O7, have been studied by T-dependent measurements of the electrical resistivity (ρ), Seebeck coefficient (S  ) and magnetization. Its structural characterization by X-ray diffraction reveals an orthorhombic crystallographic cell at room temperature (Pbn21Pbn21 space group, a=6.298 Åa=6.298 Å, b=10.939 Åb=10.939 Å and c=10.228 Åc=10.228 Å). In that structure made of corner shared CoO4 tetrahedra, the magnetic array of the cobalt cations form a 1:1 regular stacking of Kagomé and triangular layers. All the physical measurements point towards an hysteretic transition in the range 300–310 K, with a sharp increase of both S and ρ   at TSTS as the temperature decreases. A clear similarity to other LBaCo4O7LBaCo4O7 compound (L=lanthanideL=lanthanide) is found, supporting strongly the existence of a structural transition at TSTS. It is also shown that the ionic radius of the L   cation governs TSTS.

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