A. Uesawa

Spin-glass behavior in U2PtSi3

Abstract We present the DC magnetization, specific heat and magnetic relaxation measurements on well-annealed polycrystal-line sample of U 2 PtSi 3 . All the main characteristics of spin-glass behavior are observed. They are: (1) frozen-in magnetic moments below a freezing temperature T f and, hence, a peak in the field-dependent magnetization; (2) absence of visible singularity in temperature dependence of specific heat at T f ; (3) irreversibility in magnetization below T f ;(4) remanent magnetic relaxation on macroscopic time scales after changing the magnetic field below T f . The spin-glass state in U 2 PtSi 3 at low temperatures is considered to originate from the randomly frustrated U-U interactions resulting from the disordering of Pt and Si atoms on the crystallographic sites.

Spin-glass-like behavior of ternary uranium compound U2AuSi3

Abstract DC magnetization, specific heat and magnetic relaxation measurements are reported for a polycrystalline U 2 AuSi 3 . The temperature dependence of the magnetization shows a cusp at a characteristic temperature T f that strongly depends on the applied magnetic field. The specific heat does not show visible singularity around T f , ruling out the existence of the usual long range spatial magnetic order. The pronounced difference between the zero field cooled (ZFC) and the field cooled (FC) magnetization, as well as the very slow decay of the remanence indicate the occurrence of a highly irreversible frozen state below T f . These features are the characteristics of spin glass behavior.

Anisotropic behavior of magnetic and transport properties in CePdSb and CePtSb

Measurements of resistivity ρ, Hall coefficient R H , magnetic susceptibility χ, magnetization, specific heat C and magnetoresistance have been performed on the hexagonal ferromagnets CeTSb (T=Pd, Pt) and the isostructural compounds LaTSb using single crystalline samples. Strong anisotropy in ρ, ρ c >ρ a , was observed for both the Ce compounds as well as the La compounds. However, R H ( T ) for CeTSb does not exhibit strong anisotropy between H // a and H // c . The anisotropic behavior of χ( T ) for the Ce compounds is well reproduced by the crystalline electronic-field model. The analysis of χ( T ) suggests that the ferromagnetic exchange interaction along the c axis in CePdSb is much stronger than that in CePtSb. Magnetization measurements reveal that the saturated magnetic moments of 1.32 µ B and 0.91 µ B for CePdSb and CePtSb lie within the c plane in the ferromagnetic state. The C ( T ) for CePdSb shows a clear jump at T C =17.5 K in addition to a broad peak around 10 K. These results suggest that ...

X-Ray Diffraction Study on Thermal Properties of Crystal Lattices in CeP and CeAs

X-ray diffraction studies at low temperatures have been performed in order to investigate thermal properties of crystal lattices in the low-carrier-density systems cerium monopnictides. CeP and CeAs show large crystal-lattice contractions with increasing temperatures up to about 120 K and 90 K, respectively. Due to the strong p-f mixing, the excited crystal field Γ 8 -like state is expected to produce a shorter interatomic bond length between cerium ions and neighboring pnictogens than that realized by the Γ 7 ground state. The experimental results of the lattice contractions at low temperatures are explained by the thermal average of these crystal field states.

De Haas-van Alphen effect of CeSb under pressure

We report a de Haas-van Alphen effect study of CeSb in the high-field ferromagnetic (F) and intermediate-field antiferromagnetic (AFF1) phases. In the F phase, the frequencies of the electron surfaces increase monotonically with pressure. On the other hand, the frequency of one particular hole surface increases with pressure, while those of the other hole surfaces decrease slightly. The effective masses of all the hole surfaces increase similarly with pressure, while those of the electron surfaces change little. In the AFF1 phase, other hole surfaces than the particular one have qualitatively different pressure dependence from that in the F phase. The frequency changes both in the F and AFF1 phases can be explained by taking the anisotropic p-f mixing model into account. However, it is difficult to understand the changes of the effective masses in terms of the f content expected for the p-f mixing model.

X-ray diffraction studies of lattice properties in CeX (X = P and As) and Yb4As3

Abstract X-ray diffraction experiments were performed in order to study the lattice properties of the low-carrier-density strongly correlated electron systems CeX ( X = P and As) and Yb 4 As 3 . The lattice constants of CeP and CeAs take minima at 120 and 90 K, respectively. These results are explained by the model in which each crystal-field state is supposed to have its own effective ionic radius. The cell angle of Yb 4 As 3 shows the first-order-like increase from 90.0° to 90.7° accompanied with the charge ordering at T C = 288K. It gradually increases to 90.8° with decreasing temperature and is almost independent of temperature below 200 K. The temperature dependence of the cell angle is discussed in connection with the process of the charge ordering.

The anomaly in the knight shift vs susceptibility plot of 31P NMR in (CexLa1-x)P

Systematic 31 P NMR studies have been made on (Ce x La 1- x )P ( x =1.00, 0.90, 0.10, 0.02) using powders obtained from high-quality single crystals. For CeP, previously reported strong non-linearity of the Knight shift vs susceptibility plot, with an order of magnitude larger coupling constant A THI of the transferred hyperfine interaction (THI) at higher temperatures than at lower temperatures, has been confirmed to be an intrinsic property. For mixed systems, NMR spectra are composed of almost equally spaced several peaks. Detailed analyses of the spectra have shown that only the 1st-nearest-neighbor Ce ions contribute dominantly to the THI of 31 P in both the dense ( x =1.00, 0.90) and the dilute ( x =0.10, 0.02) systems. Despite this short-ranged THI, A THI varies dramatically between the two systems in quite a different way for the lower and the higher temperatures. Hence the large difference between the lower- T and the higher- T A THI in CeP becomes only a factor of ∼1.7 difference in the dilute s...

De Haas-van Alphen effect in CeP

Abstract The Fermi surface of CeP was investigated by means of the de Haas-van Alphen (dHvA) effect. In addition to the branch observed in the Schubnikov-de Haas effect with a frequency of 190 T, a new one with a rather large frequency was discovered. From a comparison with CeSb, the angular dependence of the 190 T branch suggests that it arises from the ellipsoidal electron pocket. It is this branch which corresponds to the period of anomalous multi-step magnetization driven by Landau level crossing.

Anomalous physical properties of the low carrier concentration state in f-electron systems

Abstract Recent progress in studies on low carrier concentration systems of magnetically ordered and non-magnetic heavy Fermion metals are discussed. Successive steps in the high field magnetisation, the magnetic structure, and the influence of high pressure are reported and the relation with the observed Fermi surface for CeP is discussed. The origin of the low carrier concentration in USb is also discussed based on the first observation of dHvA oscillations. It is also unambiguously demonstrated that the unconventional heavy Fermion state of Yb4As3 is intrinsic and not due to impurities.

Specific heat and de Haas-van Alphen effect in NiAs

Abstract The specific heat at the temperature range from 1.7 to 30 K and the dHvA effect at 0.55 K in the field up to 9.5 T have been measured for Pauli paramagnetic NiAs. The electronic specific heat coefficient is 3.0 mJ/(K2 mol) which is in good agreement with the value estimated from the calculated density of states. It is found that the dHvA oscillation in the field along [0001] consists of four frequencies which correspond to the extremal areas in the k-space of 0.06, 0.11, 0.16 and o.18 A−2.