J. G. Huber

Superconducting—normal phase boundaries of (La, Th)Ce systems

Abstract The dependence of the superconducting transition temperature Tc on Ce impurity concentration n is reported for various ( La, Th )Ce systems. These results document for the first time the evolution of the superconducting— normal phase boundary (Tc vs n curve) as an impurity undergoes magnetic- nonmagnetic transition which for Ce impurities in ( La, Th )Ce systems proceeds with increasing Th concentration. Observed for only the second time, re-entrant Tc vs n curves are reported for two La-rich La, Th host compositions.

The effect of nonmagnetic 4f resonances on the superconducting transition temperature:ThCe alloys

It is shown that a recent theory due to Kaiser concerning the effect of nonmagnetic resonant states on superconductivity appropriately and accurately describes the dependence of the transition temperatureTc ofThCe alloys on Ce concentration. The parameters describing thef-resonant states in the Anderson model are determined by fitting Kaisers theory to the data, and reasonable values are obtained. With the assumption that the Hartree-Fock level width remains constant under pressure, it is shown that thef level moves further above the Fermi level as the pressure is increased. This is discussed in relation to recent pressure experiments on La and La compounds containing Ce impurities.

Magnetic properties of ZrZn2 under pressure

Abstract The high field magnetization of a sample of ZrZn 1.9 was measured at pressures up to 20 kbar. Between 0 and 14 kbar the Curie temperature T 0 drops linearly from 27.6 to 9.1°K; it then curves downward and crosses the T 0 = 0 axist at critical pressure p c of 18 kbar. The spontaneous zero temperature magnetization M 0 scales with T 0 . In the ferromagnetic region M ( H , T ) is at all pressures consistent with the Stoner-Wohlfarth theory. This theory, however, does not explain the initial linear dependence of T 0 on p . The paramagnetic Curie-Weiss constant is nearly the same above and below p c .

Pressure induced loss of ferromagnetism in UPt

Abstract The weak ferromagnetic saturation moment of the intermetallic compound UPt is reduced with respect to the atmospheric pressure value by more than 90% at 20 kbar. The 30K Curie temperature is pressure independent. The paramagnetic susceptibility shows a maximum at 17 K at all pressures. Plot of x −1 vs. T above 30 K are nonlinear.

Demagnetization of Ce impurities in superconducting (La, Th)Ce alloys: Specific heat results

Detailed measurements of the specific heat jump ΔC at the superconducting transition temperatureTc as a function ofTc are reported for several (La, Th)Ce systems. The measurements document the continuous demagnetization of the Ce impurity ions which proceeds with increasing Th concentration, and provide a critical test of a theory recently developed by Müller-Hartmann and Zittartz for the superconducting behavior of matrix-impurity systems which simultaneously exhibit both superconductivity and the Kondo effect.

Low temperature specific heat of ThU

Abstract The low temperature specific heat of the weakly magnetic system Th U has been measured in both the normal and superconducting states. U impurities are found to enhanve the normal state electronic specific heat coefficient γ at an unusually large rate of 4.85 ± 0.50 mJ/mole °K2 at. % U. The specific heat jump at the superconducting transition for an alloy of composition 0.075 at. % U follows the BCS law of corresponding states suggesting that the system Th U is essentially non-magnetic at superconducting temperatures.

Magnetic susceptibility study of the continuous demagnetization of Ce impurities in the (La,Th)Ce system

Measurements of the magnetic susceptibility as a function of temperature are reported for the (La,Th)Ce system which document directly the continuous demagnetization of Ce impurities which proceeds with increasing Th composition.Ce impurities can undergo a continuous magnetic‐nonmagnetic transition when the matrix into which they have been dissolved is subjected to an external pressure or alloyed with another element.1 This effect was first observed during an experimental investigation of the pressure dependence of the superconducting transition temperature Tc of LaCe and related systems.2 Subsequently, the effect of pressure on the low temperature resistivity anomaly ρm(T) due to the Kondo effect in the LaCe system was independently studied by two groups.3,4 Unfortunately, experimental difficulties attendant to measurements at high pressure have so far prevented the acquisition of other data on this interesting system.It was later found that the continuous demagnetization of Ce impurities could also be induced by alloying the La matrix with increasing amounts of Th.5 This afforded the opportunity to measure various important physical parameters related to the demagnetization of Ce impurities in a matrix at zero applied pressure. Since then, extensive data have been accumulated for the depression of Tc with Ce concentration n,6 the depression of the specific heat jump ΔC at Tc with Tc,7 and ρm(T)8 as a function of La,Th host composition. In this paper we present magnetic susceptibility data for the (La,Th)Ce system which document the continuous demagnetization of the Ce ion directly.Measurements of the magnetic susceptibility as a function of temperature are reported for the (La,Th)Ce system which document directly the continuous demagnetization of Ce impurities which proceeds with increasing Th composition.Ce impurities can undergo a continuous magnetic‐nonmagnetic transition when the matrix into which they have been dissolved is subjected to an external pressure or alloyed with another element.1 This effect was first observed during an experimental investigation of the pressure dependence of the superconducting transition temperature Tc of LaCe and related systems.2 Subsequently, the effect of pressure on the low temperature resistivity anomaly ρm(T) due to the Kondo effect in the LaCe system was independently studied by two groups.3,4 Unfortunately, experimental difficulties attendant to measurements at high pressure have so far prevented the acquisition of other data on this interesting system.It was later found that the continuous demagnetization of Ce impurities could also be i...

Magnetic Properties of TmTe at the Pressure‐Induced Electronic Phase Transition

The susceptibility of TmTe increases continuously between 18 and 29 kbar at room temperature, while at helium temperature it increases between 29 and 39 kbar and flattens out above, indicating the existence of three separate electronic phases. The increase of the magnetization is unhysteretic and smaller than expected for a full transformation from Tm2+ to Tm3+ at all temperatures and pressures. The low temperature magnetization curves in the high pressure phases are very non‐linear.

Pressure Induced Loss of Ferromagnetism in UPt

The magnetization of the weak ferromagnet UxPt1−x was studied from x = 0.48 to x = 0.54, at temperatures between 4.5°K and 300°K, fields up to 8 kGauss and pressures up to 20 kbar. The magnetization curves were analyzed in terms of the differential paramagnetic susceptibility χd at 8 kGauss and the saturation magnetization MS. The saturation moment μs per U atom at p = 0 and T = 4.5°K is a function of x, typically of order 0.5 to 0.2μB, but only 0.07μB at x = 0.52. At T = 4.5°K, μs drops at first steeply with increasing pressure and then approaches zero asymptotically; at 20 kbar it is reduced by 94% at x = 0.50 and by 98% at x = 0.52. The Curie temperature is about 30°K and does not depend on pressure within experimental accuracy. The differential paramagnetic susceptibility has a relatively broad maximum near 17°K at all pressures and concentrations. Plots of χ−1 vs. T above 30°K curve towards the T‐axis with decreasing T for all x and p, and exhibit two nearly linear portions between 30°K and 50°K and ...

Ce impurities in Th-based superconducting hosts

The experiments reported here were initiated as a study of Ce as an impurity in Th—Y alloy hosts, motivated by an interest in observing in measurements of superconducting transition temperatures T c an expected transition of the Ce atom from a nonmagnetic configuration in Th1 to a magnetic configuration in Y.2 However, proceeding from Th to Y, the zero-pressure T c of Th—Y alloys falls below 50 m°K (our lower limit of measurement) while the Ce impurities appear to remain nonmagnetic; i.e., T c vs. Ce concentration n may always be fitted by the modified exponential