Toshiro Takabatake

Spin fluctuations in La1.85Sr0.15CuO4 studied from 119Sn Mössbauer spectroscopy

Abstract Very low temperature Mossbauer measurements were carried out for 119 Sn impurities in superconducting La 1.85 Sr 0.15 CuO 4 . A magnetic hyperfine field at Sn nucleus appears below about 7 K and the average hyperfine field at 0.02 K is estimated to be 100 k0e. The origin of the magnetic hyperfine interaction is attributed to collective spin fluctuations in the Cu oxide.

Suppression of Superconductivity in PrRh2Zn20by the Substitution of Co for Rh

Electrical resistivity ρ, magnetic susceptibility χ and specific heat C of Pr(Rh1-xCox)2Zn20 for 0 ≤ x ≤ 0.89 were measured to study the mechanism of simultaneous superconducting and antiferroquadrupolar (AFQ) transitions at Tc = TQ = 0.06 K in PrRh2Zn20. A broad peak in the magnetic specific heat Cm(T) at around 13 K is reproduced as a Schottky peak by a doublet-triplet two-levels model. However, another broad peak in Cm(T) at 1 3 K indicates splitting of the doublet state by a slight distortion of Zn cages due to the Co substitution. As a consequence of the splitting, the quadrupolar degrees of freedom must be quenched. With increasing x, Tc = 0.06 K for x = 0 is suppressed below 0.04 K for x ≥ 0.10. The suppression of Tc suggests possible interplay between the superconductivity and the quadrupolar degrees of freedom.

Effect of Ga Substitution on the Γ3Doublet Ground State in PrIr2Zn20

Electrical resistivity ρ, specific heat C, and magnetic susceptibility χ measurements are reported on PrIr2Zn20–xGax for x=0.5 and 1.0. On cooling, ρ(T)s monotonically decrease to the residual values which are two orders of magnitudes larger than that of PrIr2Zn20. A broad hump in Cm(T)s at around 10 K can be reproduced by the two-level model with the Γ3 doublet ground state and the Γ4 triplet excited state. The magnetic entropy release shifts to higher temperatures with increasing x. The increase in χ(T) at T < 5 K contrasts with the saturation of χ(T) for x=0. These observations indicate the splitting of the ground state doublet due to the lowering of the local symmetry at the Pr site by the Ga substitution.