Research of the electronstates on strongly correlated electron systems under static and dynamic extreme condition

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(1) Effect of pressure and magnetic field on the perovskite manganese oxidesMagnetostriction and magnetization of Eu_<0.58>Sr_<0.42>MnO_3 were measured under hydrostatic pressures up to 2 GPa in order to investigate the effect of pressure on the metal-insulator (M-I) transition. At ambient pressure, around 2 T and 6 K, where the field-induced M-I transition was previously reported, the observed magnetostriction was to be 0.04 %. With increasing pressure, the saturation magnetization increased at a field of 0.5 T, whereas it decreased at field of 1.5 and 5.0 T.On the other hand, the influence of hydrostatic pressure on electrical resistance of La_<0.1>Ce_<0.4>Sr_<0.5>MnO_3 were investigated under pressures up to 1.8 GPa. With increasing pressure, Curie temperature increases. It is also found that the coefficient of -logT term originated from Kondo-like effect decreases with increasing pressure and the resistance maximum temperature shifts largely to lower temperature. Though the origin of the large negative pressure coefficient cannot be clearly solved, it can be said that the peculiar phenomenon is ascribed to some kind of magnetic interactions.(2) High-pressure studies on the magnetic phase transitions and related phenomena in the single crystalline UNi_2Si_2Measurement of electrical resistance and thermal expansion under high pressure and high magnetic field were performed. We found that the analogy between the p-T and B-T magnetic phase diagrams. From the results, the critical pressure for suppression of simple antiferromagnetism in UNi_2Si_2 was determined as 3.2 GPa. It is also found that a small anomaly appears around 100 K.The resistance anomaly can be attributed to the pressure-induced magnetic order-order phase transition between ILSDW and UAF phases. In terms of magnetoelastic phenomena, thermodynamic equations and theoretical approach, it is deduced that this intermediate phase would be suppressed by applying pressure.