Pseudo-stripe ordering and its fluctuations in CMR manganites

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In order to elucidate the mechanism of the colossal magnetoresistance, we have been studying charge/orbital ordering with use of neutron scattering technique. We also studied pseudo-stripe ordering and checkerboard charge ordering in two dimensional Ni oxides.In the study of the (A_1-xB_x)MnO_3 tyoe manganites, we separately studied the effect of randomness in the A/B ion site by preparing the alternately ordered layered manganites in which layers of wither A ions stack alternately. This class of manganites with no A-site randomness shows the highest charge ordering transition temperature. In addition, we discovered that the charge ordering transition and the structural transition take place independently.By the study of the two dimensional Ni oxide La_2-xSr_xNiO_4, we discovered that the checkerboard type charge order is formed at〜480K, but it is replaced by the stripe type spin/charge ordering at low temperatures. the insulator to metal transition in this material is driven not by the stripe order but by the CB charge order.