Akiko Ishiguro

Fermi surface of the heavy-fermion superconductor UPd2Al3

Abstract UPd2Al3 is a heavy fermion superconductor with T c ≊ 2 K co-existent with an antiferromagnetically ordered state (TN = 14.5 K. We report the angular dependence of the dHvA frequency, the effective cyclotron mass and the Dingle temperature. A comparison of the experimental results with band-structure calculations is made, revealing that 5f electrons in UPd2Al3 are fairly itinerant.

Anomalous Susceptibility of UPd2Al3 near the Upper Critical Field.

The ac susceptibility of the heavy fermion superconductor UPd 2 Al 3 has been measured. The peak of the susceptibility has been observed in the vicinity of the upper critical field. This anomaly is explained by the flux pinning rather than by the Fulde-Ferrell state.

dHvA effect on UPd2Al3

Abstract UPd 2 Al 3 is a heavy-fermion superconductor with T c ≅ 2 K coexistent with an antiferromagnetically ordered state ( T N = 14.5 K). We have succeeded in observing the de Haas-van Alphen (dHvA) effect on UPd 2 Al 3 for the first time. In this paper, we report the angular dependence of the dHvA frequency. It is also shown that five branches are observed and effective cyclotron masses are found to range approximately from 10 m 0 to 32 m 0 . The amplitude of the dHvA signals depends strongly on the magnetic field direction.

Magnetic, electrical and thermal properties of heavy fermion superconductor UPd/sub 2/Al/sub 3/

We report experimental results of electrical resistivity, de Haas-van Alphen effect, specific heat and thermal expansion of UPd/sub 2/Al/sub 3/. The nominal composition is denoted by the formula of UPd/sub 2+x/Al/sub 3+y/. Samples with the composition of UPd/sub 2/Al/sub 3.03/ and UPd/sub 2.02/Al/sub 3.03/ reveal de Haas-van Alphen oscillations of the magnetic susceptibility. An anomaly is observed in the superconducting phase in the temperature dependence of the specific heat and thermal expansion of UPd/sub 2/Al/sub 3.03/. The relation between the sample quality and the appearance of the anomaly is discussed. >

Two-axis goniometer for use in the mixing chamber of a dilution refrigerator

Abstract We have constructed a goniometer to rotate a sample around two independent axes in the mixing chamber of a dilution refrigerator. Two small computer-controlled stepper motors wound with superconducting wire rotate the sample around the axes with an angular range of 360 °. The goniometer was designed to investigate the angular dependence of the magnetic de Haas-van Alphen effect of heavy electron materials in a magnetic field of up to 14.5 T.

de Haas-van Alphen effect and Fermi surfaces of magnetic dense-kondo compound CeNi2Al5

The experiments of de Haas-van Alphen (dHvA) effect have been carried out at temperatures down to 40 mK in a magnetic dense-Kondo compound CeNi 2 Al 5 with an incommensurate magnetic structure. A complex phase diagram of the magnetic transition field versus temperature is completed. Many branches of the dHvA frequencies observed in the higher-field regions, II, III and IV, have been understood better by the branches predicted from the theoretical Fermi surfaces of nonmagnetic reference-sample LaNi 2 Al 5 rather than the theoretical ones in CeNi 2 Al 5 with 4 f electrons treated as itinerant. Branches observed in the lowest field region I are not clearly analyzed with the theoretical prediction in LaNi 2 Al 5 or CeNi 2 Al 5 . The electrons with heavy cyclotron mass are observed in the region IV; 12.4 m 0 in η branch, 11.2 m 0 in ζ branch and 9.6 m 0 in θ branch. Some pairs of parallel branches are observed due to the spin-splitting related to the magnetism, and the exchange energy Δ E is obtained; Δ E =12....

de Haas-van Alphen Effect and Fermi Surface of USb

The de Haas-van Alphen effect has been measured in a semimetallic compound USb from at temperatures down to 45 mK and in fields up to 13.5 T. The observed three kinds of signal branches indicate that there exist two sets of ellipsoidal Fermi surfaces with different sizes and one spherical Fermi surface. The measured effective mass ratios m * / m 0 are in the range between 0.9 and 2.7.

Possible quadrupolar ordering in a Kondo-lattice compound Ce3Pd20Ge6

Abstract We measured the electrical resistivity and the low-temperature specific heat, C p of two single crystalline samples of Ce 3 Pd 20 Ge 6 in applied magnetic fields in order to clarify the nature of the anomaly previously found around 1.2 K in C p of polycrystalline samples. The anomaly is believed to be due to quadropolar ordering of the Γ 8 quarter crystralline-field ground state of Ce ions. We found that the anomaly is broadened and shiftedto higher temperatures as the field is increased. The results are briefly discussed by comparing with those of CeB 6 .

De Haas-van Alphen effect in CoS2

Abstract We present the first measurement of the de Haas-van Alphen (dHvA) effect in CoS 2 at temperatures down to 50 mK and in fields up to 13.5 T. It was found that mainly five kinds of branches exist and the largest effective mass is about 5.0 m 0 . The experimental result agree with the result of the band calculation at high dHvA frequencies, except at low frequencies.

dHvA effect on U3As4

Abstract We are investigating the delocalization of 5ƒ electrons in uranium compounds by means of the de Haas-van Alphen(dHvA) experiment. The measurements of moderately-heavy fermion compound U3 P4 show the complicated angular dependence of the cross-sectional area of the Fermi surface. By contrast, the angular dependence in U3 As4 seems rather simple, corresponding to the smaller electronic specific heat coefficient. This result seems to be due to weaker hybridization of 5ƒ electrons with ligands in U3 As4 than in U3 P4.