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The effect of magnetic field on the pseudogap in the Kondo semimetal CeNiSn has been reinvestigated by the measurement of magnetization and longitudinal magnetoresistance in pulsed high magnetic fields applied along the principal crystallographic directions of the orthorhombic structure. By extending the field range up to 65 T, metamagnetic behaviors at 45 and 60 T are observed for the first time along the easy magnetization direction of a -axis. No anomaly is found, on the other hand, along the b - and c -axes up to 55 T. The magnetoresistance along the a -axis exhibits the minimum at about 30 T and increases above 40 T, which is in accord with the anomalous increase of the magnetization. By contrast, the magnetoresistance along the b - and c -axes shows only a monotonous decrease above 10 T. These results are discussed in terms of a Zeeman splitting of the double-gapped density of states derived from the anisotropic hybridization-gap model.

We report a systematic study of thermoelectric properties of a series of Ce-based compounds with the e -TiNiSi-type structure; metallic CePtSn, semimetallic CeNiSn and CeRhSb, and semiconducting CeRhAs. In this sequence, both the Kondo temperature and hybridization-gap width increase, whereas the phonon thermal conductivity at high temperatures decreases. Opening of the pseudogap in CeRhSb and CeRhAs enlarges the thermopower, and leads to the maxima of the thermoelectric figure of merit, 1.7×10 −3 /K at 12 K and 1.0×10 −3 /K at 115 K, respectively.

We have performed magnetoresistance measurements on an organic conductor, α-(BEDT-TTF)2KHg(SCN)4, and on a Kondo semiconductor, CeNiSn, at low temperatures and for fields up to 45 T in the hybrid magnet at the National High Magnetic Field Laboratory. We will discuss some new insight into a very controversial high-field phase of α-(BEDT-TTF)2KHg(SCN)4 gained from measurements of the anomalous temperature dependence of the quantum oscillations in the range 25–45 T. New information will also be presented on the temperature dependence of resistivity in the high-field state of CeNiSn, where questions of metallic versus semiconducting ground states arise. To acquaint researchers who anticipate using the facility in the near future, practical details concerning use of this new high-field resource are included.

We have studied a metamagnetic-like anomaly in CeNiSn via measurements of transverse and longitudinal magnetoresistance (MR) and AC magnetic susceptibility (χ) in a wide range of temperature T, magnetic field B, and pressure p, i.e., 0.05 K⩽ T ⩽0.9 K , 0⩽ B ⩽20 T , and 0⩽ p ⩽10 kbar . We identify five field regions in which both MR and χ exhibit anomalous behavior, i.e., distinct deviation from monotonous variation as a function of B. The disparate pressure dependence of each regime cannot be explained by the pressure variation of a single parameter, viz., the Kondo temperature, and suggests that the metamagnetic-like anomaly in CeNiSn is a combination of anomalies of different origins.

We report on the magnetic, transport and thermal measurements for a single-crystal sample of CeNi0.82Cu0.18Sn. An antiferromagnetic order below T N =3.5 K is observed in magnetic susceptibility χ, specific heat C and electrical resistivity. The specific heat jump at TN is only 0.7 J/mol K and a large value of C/T=380 mJ/mol K 2 remains at 0.5 K. The strong magnetic anisotropy, χ a >χ b >χ c , is similar to that for the host compound CeNiSn. From the analysis of χ(T), we derived a set of crystal-field parameters, which yield the ground state consisting mainly of |J Z 〉=|±5/2〉.

We report the observation of an unexpected magnetic transition in the Kondo semimetal CeNiSn under uniaxial pressures. For $P\ensuremath{\parallel}a,$ both the specific heat C and magnetic susceptibility \ensuremath{\chi} decrease steadily with increasing P. By contrast, once $P\ensuremath{\parallel}b$ and $P\ensuremath{\parallel}c$ exceed 0.13 GPa, $C(T)$ exhibits a distinct jump at 4 K followed by a peak at 3 K. The concomitant peaking in $\ensuremath{\chi}(T)$ for $P\ensuremath{\parallel}B\ensuremath{\parallel}c$ is indicative of an antiferromagnetic transition.

Kondo semiconductors are a class of strongly correlated f-electron materials whose low-energy excitations exhibit a (pseudo)gap at low temperatures. The significant difference between the pseudogap in orthorhombic CeNiSn and CeRhSb and the real gap in cubic Ce 3 Bi 4 Pt 3 and YbB 12 is highlighted by a comparison of transport properties. Low-temparature measurements of the magnetoresistance, Hall coefficient and specific heat of CeNiSn have revealed a field-induced excitation of the coherent low-carrier state. A systematic study of CeNi 1− x T x Sn ( T = Co, Cu and Pt ) has shown that the residual carriers in CeNiSn are immobilized by 1% substitution irrespective of the substitutes. Further substitution with 5% Cu induces a magnetic instability at T = 0.

We present thermal-conductivity $\ensuremath{\kappa}$ and thermopower S measurements on high-quality single crystalline CeNiSn along the three crystallographic axes $a, b,$ and c in the temperature range between 100 mK and 7 K and in magnetic fields up to 8 T applied along the a axis. Both $\ensuremath{\kappa}$ and S are highly anisotropic. However, characteristic features that may be attributed to the opening of a pseudogap in the electronic density of states (DOS) at the Fermi energy $\ensuremath{\eta}$ below 10 K are seen for all three crystallographic directions. These features are strongly suppressed by a magnetic field of 8 T applied along the a axis. At the lowest temperatures we have evidence for the presence of a residual metallic DOS at $\ensuremath{\eta},$ again for all three directions. The saturation of the reduced Lorenz number ${L/L}_{0}$ to a value distinctly higher than one is an interesting feature which deserves further investigation.

We report on measurements of the specific heat C and magnetization M of CeNi1−xCuxSn single crystals for T K . For x=0.05 an increase of C/T and M (measured in a magnetic field B=0.1 T applied parallel to the a-direction) towards low T down to 0.1 K indicates absence of magnetic order while for x=0.078 a maximum in M is found at T M ∼0.39 K . The magnetization M(B) for both crystals measured at 0.3 K along the a-direction increases linearly up to 7 T without any indication of saturation except for a small superimposed Brillouin-like feature. The critical concentration for the onset of magnetic order is estimated to xc=0.065.

Among rare-earth-based compounds showing the Kondo effect, systems exhibiting a small energy gap in the heavy-electron band are referred to as Kondo semiconductors. We have measured thermoelectric properties of CeNiSn, CeRhSb, CeRhAs, YbB/sub 12/ and their substituted alloys. The thermopower of CeRhAs has a positive maximum of 130 /spl mu/V/K at 40 K, while that of YbB/sub 12/ has a negative peak of -150 /spl mu/V/K at 10 K. For both CeNiSn and CeRhSb, the electrical resistivity is less than 200 /spl mu//spl Omega/cm and the thermal conductivity is about 50 mW/Kcm at 60 K. The figure of merit Z for CeRhAs and CeRhSb has the maximum value of 1.0/spl times/10/sup -3//K at 125 K and 2.2/spl times/10/sup -3//K at 13 K, respectively. Therefore, these compounds have high potential for a novel thermoelectric cooling material at low temperatures.