Makio Kurisu

Pressure dependences of superconducting transition temperature Tc in orthorhombic and impurity-induced tetragonal YBa2(Cu1−xMx)3O7−y (M=Fe, Co, Ni and Zn)

Abstract The pressure dependences of the superconducting transition temperature Tc of both orthorhombic and impurity-induced tetragonal YBa2(Cu1−xMx)3O7−y (M=Fe, Co, Ni and Zn) are studied by electrical resistance measurements under hydrostatic pressure up to 30 kbar. A strong correlation between the pressure dependence of Tc and the crystal structure is found: the rate of pressure enhancement of Tc, dTc/dP, is four times larger for the tretragonal phase than for the orthorhombic phase; neither the choice of the dopant, the amount of doping x, nor the magnitude of Tc at P=O kbar is the major factor to determine the pressure effect of Tc.

Magnetic and Structural Properties of CeAg at High Pressure

Electrical resistivity of the cubic CsCl-type ferromagnetic compound CeAg was measured at hydrostatic pressures p s up to 18 kbar and in temperatures from 1.6 K to 300 K. For p <2.2 kbar, the structural transition temperature from cubic to tetragonal was not accompanied with hysteresis and was pressure independent. For p ≥2.2 kbar, the transition temperature increased largely with p , accompanied with wide hysteresis. These trends of pressure dependences are discussed based on the Jahn-Teller distortion model in reference to the alloying effect, CeAg 1- x In x . The Curie temperature T c increased rather rapidly at 2.2 kbar and took a maximum value around 7 kbar. The spin disordered resistivity increased rapidly at 2.2 kbar, but linearly with relatively small gradient above it. The correlation between magnetic and structural transition phenomena are analysed qualitatively, by taking above-mentioned results into account.

Magnetic and structural phase transition of CeCd at hydrostatic pressure

Abstract Hydrostatic pressure effects on the Curie temperature T c and two successive structural phase transition temperatures T M of CeCd were determined from both electric and magnetic measurements from 1.6 to 300 K at pressures up to 12 kbar. With increasing pressure, T c decreases, in contrast to the result of CeAg, and the T M s increase rapidly.

Magnetization of CeAg at high pressure

Abstract Magnetization measurements for CeAg under hydrostatic pressures up to 4.0 kbar and CeAg1−xInx compounds (0.01 ⩽ x ⩽ 0.20) at normal pressure were made at 4.2 K in magnetic fields up to 50 kOe. It was found that the magnetization of CeAg under pressure and of CeAg1−xInx were larger than that of CeAg at normal pressure.

Magnetic and structural phase transition of CeAg at hydrostatic pressure

Abstract Pressure effects on the Curie temperature and the crystallographic phase transition temperature of CeAg were determined from an electrical resistivity measurement from 4.2 to 300 K at hydrostatic pressures up to 5 kb. Results correspond to the alloying effect in Ce(Ag,In).

Structural phase transitions in YCu1−xMx (M = Ni, Ag and Ga)

Abstract The structural phase transitions in YCu 1− x M x (M = Ni, Ag and Ga) have been investigated from the measurements of the electrical resistivity at nnormal and high pressures, the thermal expansion and X-ray analysis. YCu has a very large thermal hysteresis width (about 400 K) associated with the structural transition. With increasing x the transition temperatures to the low and to the high temperature phases increase for YCu 1− x M x with M = Ni and decrease for M = Ag and Ga. The low temperature phase is likely to be of the FeB type.

Magnetic and Structural Properties of CeTl at Hydrostatic Pressure

The electrical resistivity, ac magnetic susceptibility and magnetization of CeTl were measured at pressures up to 17 kbar. At ambient pressure the cubic to tetragonal transition occurs at T M =193 K and antiferromagnetic state with a metamagnetic character below the Neel temperature T N =25.5 K. When pressure p increases, T M increases at a rate of d T M /d p =+19 K/kbar, T N decreases at a rate of d T N /d p =-0.28 K/kbar and metamagnetic transition field H c at 4.2 K decreases from 20 kOe at ambient pressure. Above about 10 kbar, pressure-induced ferromagnetic phase appears and its Curie temperature T c increases at a rate of d T c /d p =+0.10 K/kbar.

Structural phase transition in CsCl-type RM compounds (R=La, Ce, Pr, Nd; M=Ag, Cd, Tl)

The data on the structural transition temperature at ambient pressure, the pressure effect and the alloying effect (RAg1-xInx) in CsCl-type compounds RM (R=La, Ce, Pr, Nd; M=Ag, Cd, Tl) are summarised. The R dependence shows common tendencies, which strongly suggests that the d-character electron in the 5d6s band of R plays an important role in the structural transition.

Hydrostatic pressure study on magnetic and structural phase properties of CeAg up to 37 kbar

Abstract Regarding the pressure dependence of the ferromagnetic Curie temperature T c in the pressure-induced phase of CeAg, it is found from the electrical resistivity measurement under hydrostatic pressures up to 37 kbar that T c in the tetragonal phase takes a maximum at ≈ 7 kbar and it increases, showing a Kondo anomaly, above 20 kbar at which an unidentified new phase develops.

Kondo anomaly and metamagnetism of CeZn2 at high pressure

Abstract A pressure study has been made on the metamagnetic Kondo system CeZn 2 with Neel temperature T N of 7.5 K. Measurements were carried out on the electrical resistivity and T N up to pressure p of about 30 kbar, and on the single crystal magnetization up to pressure of 14 kbar. Results obtained are as follows: (i) The Kondo anomaly is enhanced with application of p . (ii) T N increases with pressure first up to 15 kbar and is likely to saturate or to start decreasing around 30 kbar. (iii) Metamagnetic transition with many steps which is possibly an example of Devils staircase character changes largely with p . Subsequently the (pressure)-(magnetic field) phase diagram is constructed. These results have been qualitatively discussed on lines described in our previous studies on CeZn 2 at normal pressure and on other Ce-based compounds.