Sung Won Yun

Anomalous thermal expansion of single-crystalline UGe2

The linear thermal expansion coefficients α of single-crystalline UGe2 have been measured in the temperature range 6 K <T<300 K. It is found that α exhibits a large anisotropy in the temperature dependence and a discontinous change near 50 K (=Tc), which corresponds to ferromagnetic order. The volume of UGe2 increases with decreasing temperature below Tc. The magnitude of spontaneous volume magnetostriction is about 1.2 × 10−3 at 0 K.

Magnetic and Electrical Properties of UPd3

We have measured the electrical resistivity, Hall coefficient, thermoelectric power, magnetic susceptibility, magnetization, specific heat, magnetoresistance and de Haas-van Alphen (dHvA) oscillation of UPd 3 to clarify the magnetic and Fermi surface properties. A phase transition, which occurs at about 4.5 K, is most likely related to the antiferromagnetic ordering because the magnetic specific heat shows a T 3 dependence below 2 K. About ten different dHvA branches ranging from 1.8 ×10 5 Oe to 7.5 ×10 7 Oe have been observed. From the angular dependence of dHvA frequency, UPd 3 is found to consist of the closed spherical Fermi surfaces and multiply-connected ones. The cyclotron masses are light, ranging from 0.5 m 0 to 3.6 m 0 , which indicate the localized f electron character.

Electrical resistivity of single crystalline UGe2 at high pressure and high magnetic field

Abstract Electrical resistivity ϱ(T) of single crystalline UGe2 has been measured at high pressure up to 20 kbar and high magnetic field to 5 T. It was found that the Curie temperature Tc (K) decreases with increasing pressure and tends to disappear around 18 kbar. The magnitude of magnetoresistance Δϱ/ϱ decreases with pressure. The result is discussed briefly on the basis of the theory of weak itinerant ferromagnetism.

Effect of pressure on magnetic ordering in UGe2

Abstract The electrical resistivity of the ferromagnetic compound UGe 2 ( T C =52 K) has been measured under high pressure up to 8 GPa. T C is suppressed by pressure and the spin fluctuation model can be applied for the low-temperature region. The low-temperature resistivity can be understood on the basis of the spin fluctuation model. The normalized resistivity is found to scale with a characteristic temperature.

Anomalous Hall Coefficient in the f Electron System

The 4f(5f) electrons in the rare earth(uranium) atom are pushed deep into the interior of the closed 5s(6s) and 5p(6p) shells because of the strong centrifugal potential 1(1+1)/r2 , where 1=3 holds for the f electrons. This is a reason why the 4f (5f) electrons possess an atomic-like character even in the compound. On the other hand, the tail of their wave function spreads to the outside of the closed 5s(6s) and 5p(6p) shells, which is highly influenced by the potential energy, the relativistic effect, the distance between the rare earth(uranium) atoms, and hybridization of the 4f(5f) electrons with the conduction electrons. These cause the various phenomena such as valence and spin fluctuations, gap states, Kondo lattice, heavy electrons (fermion), metamagnetism and superconductivity for the f electron compounds.1

Effect of pressure on the Curie temperature of single-crystal UGe2

The linear thermal expansion of single-crystal UGe2 has been measured in the temperature range 4.2 K < T < 300 K under high pressure up to 20 kbar. The linear thermal expansion coefficient αi (K−1) (i = a, b and c) exhibits a discontinuity near 50 K and a large anisotropy, which corresponds to ferromagnetic order. The discontinuous changes in the values of αa, αb and αc at Tc are 25 × 10−6K−1, 40 × 10−6K−1 and −10 × 10−6K−1 respectively. It is found that Tc decreases with increasing pressure and becomes lower than 4.2 K at 20 kbar. The initial decreasing rate of Tc was estimated to be dTcdP = −0.7 K kbar−1. The data are analysed briefly by assuming a weak ferromagnetic theory.

Heavy cyclotron mass in ferromagnetic substance UGe2

Abstract We have measured transverse magnetoresistance and the de Haas-van Alphen effect in an anisotropic ferromagnetic substance UGe 2 . Fermi surfaces consist of multiple-connected large cylindrical sheets and ellipsoidal closed ones. Carriers possess large cyclotron effective masses, ranging from 2 to 2 m 0 .

Electrical and magnetic properties of U-X (X = Ru, Rh and Ir) intermetallic compounds

We have studied the electrical and magnetic properties of U–X (X=Ru, Rh and Ir) intermetallic compounds by measuring the electrical resistivity, Hall coefficient, thermoelectric power, specific heat, magnetic susceptibility and magnetization. We have found a variety of behaviors of antiferromagnetism, ferromagnetism and superconductivity in these compounds.

High-quality single-crystal growth and Fermi surface properties of UGe2

Abstract We have grown a high-quality single crystal of UGe 2 with a residual resistivity ratio of 910 by the ‘tri-arc’ pulling method and annealing process.

Fermi surface properties of UPd3

Abstract From the angular dependence of the de Haas-van Alphen frequency, UPd 3 is found to consist of closed spherical Fermi surfaces and multiply connected ones. The cyclotron masses are in the range (0.5–3.6) m 0 .