K. Bakker

Anisotropic variation of Tc and TN in URu2Si2 by uniaxial pressure

Abstract The effect of uniaxial stress on the superconducting and magnetic transition temperature in the heavy-fermion system URu2Si2 has been investigated by means of resistivity measurements. The uniaxial pressure effects on Tc and TN are inversely connected: Tc increases and TN decreases for a stress along the tetragonal axis, while a stress in the plane results in the opposite effect.

Impurity effects in superconducting UPt3

Superconducting UPt3 is characterized by a novel and complex magnetic field‐temperature phase diagram, with two superconducting transitions at Tc1 and Tc2 in zero field. We have studied the effects of Pd and Y impurities on the zero field superconducting properties of UPt3. Resistance measurements show that both dopants increase the residual resistivity and decrease the spin fluctuation temperature in the normal state. Tc1 is depressed by both dopants, but more effectively by Pd. ‖Tc1 − Tc2‖ is essentially unaffected by Y doping, but increases dramatically with Pd doping.

High-field magnetoresistance of heavy-fermion UPd2Al3

We report on high-field (B<38 T) magnetoresistance experiments on a single-crystalline sample of the heavy-fermion antiferromagnet UPd2Al3 (TN = 14 K) at liquid-helium temperatures. The antiferromagnetic phase boundary, previously detected by magnetization measurements at Bc = 18 T for a field in the basal plane (t = 1.3 K), is reflected as a sharp peak in the longitudinal (I|a) and as a precipitous drop in the transverse (I|c) magnetoresistance.

Hall effect of URu2Si2 in very high magnetic fields up to 40.5 T

Abstract The Hall coefficient ( R H ) of the heavy-fermion compound URu 2 Si 2 has been measured in very high magnetic fields directed along the tetragonal axis at temperatures of 0.6, 1.5 and 4.2 K. At low fields, R H =15×10 -3 cm 3 /C, but is reduced to almost zero in the high-field limit (40.5 T). The three high-field transitions, previously observed in the magnetization and the magnetoresistance, are also identified in the Hall resistance at fields of 35.6, 36.2 and 39.2 T at T =1.5 K.

The effect of pressure on the antiferromagnetic and superconducting states of heavy-fermion UPd2Al3

Abstract The effect of a hydrostatic pressure ( p ≤ 3.5 bar) on the antiferromagnetic ( T N = 14.2 K) and superconducting transition ( T c = 1.9 K) temperature of single-crystalline UPd 2 Al 3 has been determined by means of resistivity measurements. The pressure effects are extremely small when compared to other heavy-fermion systems: d T N /d p = 0 ± 3 mK kbar −1 and d T c /d p = −2.0 ± 0.7 mK kbar −1 . The effect of a hydrostatic pressure ( p ≤ 5 kbar) on the antiferromagnetic phase boundary has been studied by means of high-field magnetization measurements ( B ≤ 28 T). It is found that the antiferromagnetic phase boundary, which is located at B c = 18 T for a field in the hexagonal plane at T = 5 K, shifts to higher field values with pressure at a rate of 0.13 ± 0.01 T kbar −1 .

Magnetic and transport properties of U1−xCexRu2Si2

Abstract Pseudoternary compounds of the heavy fermion series U 1− x Ce x Ru 2 Si 2 ( x ⩽0.1 and x ⩾0.9) have been characterized by means of electrical resistivity and magnetic susceptibility measurements. High field magnetization measurements revealed an increase of the metamagnetic-like transition field of CeRu 2 Si 2 by allowing with U, and a suppression of the three-step magnetization process in URu 2 Si 2 by alloying with Ce. The influence of chemical pressure is investigated.

Anomalous negative thermal expansion of CeInCu2

Abstract The coefficients of linear thermal expansion, α(T), of the heavy-fermion compound CeInCu2 and its non-heavy analog LaInCu2 have been measured at low temperatures (0.3 K

Double superconducting transition in the specific heat of non-stoichiometric UPt3+x

We have studied the double superconducting transition of polycrystalline UPt3+x prepared from a non-stoichiometric melt (−0.06 < x < 0.06). Samples prepared with a Pt deficit show the sharpest double transition, suggesting the binding of oxygen by excess uranium. However, microprobe investigations reveal that impurity phases (UPt2 and UPt5) are formed and that the actual deviation from stoichiometry (−0.01 < x < 0.01) is much smaller than the nominal value.

On the magnetic and superconducting phases of heavy-fermion UPt3

Abstract The electronic instability in the height correlated electron system UPt3 gives rise to various intriguing phenomena at liquid-helium temperatures, among which the occurrence of unconventional superconductivity (T+c = 0.49 K, T-c = 0.44 K) has attracted most attention. In a magnetic field three superconducting phases are observed that meet at a tetracritical point. We here present a discussion of a number of puzzling aspects of a superconducting phase diagram (B⊥c) of unprecedented accuracy, determined by dilatometry. The possible interplay of superconductivity and reduced moment antiferromagnetism (TN = 5K) is investigated. Furthermore, we report on recent studies of the suppression of Tc, by alloying with Pd, Y, Th, Au and Ir.

Anisotropic low-field magnetization of heavy-fermion superconductor URu/sub 2/Si/sub 2/

Using a sensitive Hall-probe technique, the magnetization anisotropy of the heavy-fermion superconductor URu/sub 2/Si/sub 2/, with T/sub c/=1.2 K, was studied as a function of magnetic field and temperature on a cube-shaped sample. The estimated first-critical-field values, H/sub c1/, extrapolated to T=0 are about 10 and 15 Oe for field parallel to the a- and c-crystallographic directions, respectively. The low-field critical-current density, J/sub c/, exhibits a similar anisotropy as H/sub c1/ but J/sub c/ is suppressed in particular by magnetic field oriented along the c-direction. It is argued that results of magnetization measurements should depend on the sample size and shape. >