Investigation of exotic electronic properties on rare-earth & actinide compounds under high pressure

We have synthesized and investigated electronic properties of several non-centrosymmetric actinide compounds, which do not have an inversion center in the crystal structure “globally” or “locally”, under high pressure. The Néel temperature of an antiferromagnet UIrSi3 with “globally” non-centrosymmetric structure increases with increasing pressure at a rate of 2.5 K/GPa up to 5 GPa. On the other hand, TNs of U2Rh3Si5 and U2Ir3Si5, which are “locally” non-centrosymmetric compounds, decrease with -1 K/GPa and -0.5 K/GPa with increasing pressure, respectively. Here, U2Ir3Si5 is a new antiferromagnet crystallizing in the U2Co3Si5-type of orthorhombic structure. Below TN = 36.5 K, U2Ir3Si5 shows magnetic order-order transition at T0 = 26.1 K with a first-order nature. Electrical resistivity in U2Ir3Si5 shows semiconducting-like behavior due to the formation of the super-zone gap in the antiferromagnetic state. TN and T0 as well as semi-conducting-like behavior in resistivity are suppressed by external pressure.