Spin, charge, and lattice coupling in triangular and Kagomé sublattices ofCoO4tetrahedra:YbBaCo4O7+δ(δ=0,1) (original) (raw)

The structural and physical properties of YbBaCo 4 O 7+␦ have been studied. The polycrystalline samples of this "114" phase of composition Yb 0.95 BaCo 4 O 7+␦ have been prepared in air. By postannealing, two samples corresponding to ␦ ϳ 0 and ␦ ϳ 1 have been obtained. The physical properties of the compound "O 7 " ͑␦ ϳ 0͒ exhibit a hysteretic transition at T S = 160 K-180 K as a function of T as shown by resistivity, magnetization, and thermoelectric power measurements. These measurements indicate a hole-doped electrical conduction compatible with an activated regime for the hopping of high spin Co 3+ holes in a matrix of high spin Co 2+. By increasing the oxygen content, i.e., the cobalt oxidation state from 2.25 for "O 7 " to 2.75 for "O 8 ," the signatures of this transition are suppressed. This shows that below the structural transition at T S , the release of the magnetic frustration helps the development of antiferromagnetic order. The latter in turn creates the charge localization at T S .