K. Hiraoka

NMR study of YbCdCu4 and YbTlCu4

Abstract In the C15b-type compound YbCdCu 4 the nuclear spin-lattice relaxation rates T 1 −1 for 113 Cd and 63 Cu (NQR) suggest a gradual change with temperature of 4f electron states from itinerant to localized ones. In YbTlCu 4 a nearly temperature-independent 205 Tl Knight shift and T 1 T = constant law for 205 Tl and 63 Cu indicate the itinerancy of 4f electrons.

Pressure effect on valence phase transition of YbInCu4

Abstract The electrical resistance of YbInCu 4 has been measured as a function of temperature under various pressures from 1.5 to 8 GPa. The temperature of the valence phase transition decreases almost linearly with pressure up to 1.5 GPa and is depressed to temperatures below 4.2 K above 3 GPa, where it decreases more gradually.

Magnetic phase transitions in the Gd(Mn1 − xCox)2 system

Abstract Measurements of magnetization, ac susceptibility, thermal expansion, specific heat and NMR have been carried out on the cubic Laves-phase compounds Gd(Mn 1 - x Co x ) 2 . The substitution of Co for Mn makes the antiferromagnetic coupling between Mn moments unstable and results in the ferromagnetic arrangement of 3d moments above x = 0.35. The results are discussed on the basis of the itinerant 3d-electron model. On the other hand, the Gd moments in the ground state are in a freezing state with a random configuration for 0 ≤ x ≤ 0.025, in a canted state for 0.05 ≤ x x ≥ 0.35. The freezing state of Gd moments for x ≤ 0.025 may be realized by slight but intrinsic randomness in the arrangement of atoms in addition to the competing state of the exchange interactions.

Temperature dependences of the Knight shifts in Ce monopnictides

Abstract The 75As Knight shift 75 K(T) in CeAs shows an anomalous change between 25 and 70 K, which is due to a large difference between the hyperfine couplings in the crystal field split γ7 and γ8 states. In CeSb and CeBi, K(T) of Sb and 209Bi exhibit Curie-Weiss-like behaviours, probably because of much smaller crystal field splittings

31P NMR study of dense Kondo compound CeP

Abstract The 31 P Knight shift vs susceptibility curve in CeP exhibits remarkably different slopes below 30 K and above 80 K, yielding the hyperfine coupling constants of 0.95 and 9.3 kOe/μ B in the crystalline Γ 7 and Γ 8 states, respectively. The high temperature behaviors of the nuclear relaxation rate 1/ T 1 indicate a low carrier concentration as well as the localized nature of Ce 4f electrons. 1/ T 1 exhibits a critical divergence of T 1 T α( T − T N ) 0.56 below 30 K.

77Se NMR study of CeSe

Abstract The 77 Se Knight shift K ( T ) in CeSe exhibits a Curie-Weiss-like behavior above 20 K, and a plot of K ( T ) against susceptibility yields a hyperfine field of 11.0 kOe/μ B . The nuclear spin-lattice relaxation rate T 1 −1 is independent of temperature at high temperatures. The NMR results suggest the localized nature of Ce 4f electrons.

Pressure dependence of the 31P and 75As Knights shifts in CeP and CeAs

Abstract Pressure effects on the 31P and 75As Knight shifts K in CeP and CeAs were studied up to 8.6 kbar. At 8.6 kbar 31 K(T) exhibits a Curie-Weiss-like behaviour similar to that of 121 K(T) in CeSb at ambient pressure, suggesting a decrease in the crystal field γ7-γ8 splitting. In CeAs 75 K(T) is much less sensitive to pressure.