Yu Yamane

Competing Magnetic Interactions in the Kramers Doublet System NdIr2Zn20

Electrical resistivity ρ, magnetization M, and specific heat C measurements are reported for single-crystalline samples of the 4f3 Kramers system NdIr2Zn20. On cooling, ρ(T) monotonically decreases and drops below 0.65 K. The magnetic susceptibility M/B follows the Curie–Weiss law from 300 to 20 K, leading to an effective magnetic moment of μeff = 3.59 μB/Nd and a paramagnetic Curie temperature of θp = −3.6 K. The negative value of θp indicates an antiferro-type interaction, although the enhancement of M(B) in the paramagnetic state implies a ferro-type one. A broad maximum in the magnetic specific heat Cm at around 15 K arises from the excitations from the crystalline electric field ground state of a magnetic Γ6 doublet to the excited Γ8 quartet lying at 39 K above the ground state. A sharp peak in C(T) at 0.65 K coincides with the drop in ρ(T), both of which shift to lower temperatures upon applying a magnetic field. The field dependences indicate that an antiferromagnetic order may occur under the geom...

Single-Site Non-Fermi Liquid Behaviors in a Diluted 4

Electrical resistivity ρ(T) and specific heat C(T) measurements have been made on the diluted 4f^{2} system Y(Pr)Ir_{2}Zn_{20}. Both data of ρ and magnetic specific heat C_{m} per Pr ion are well scaled as a function of T/T_{0}, where T_{0} is a characteristic temperature of non-Fermi-liquid (NFL) behaviors. Furthermore, the temperature dependences of ρ and C_{m}/T agree with the NFL behaviors predicted by the two-channel Kondo model for the strong coupling limit. Therefore, we infer that the observed NFL behaviors result from the single-site quadrupole Kondo effect due to the hybridization of the 4f^{2} states with multichannel conduction electrons.

f^2

The specific heat of Y1-xPrxIr2Zn20 with x = 0.044 has been measured down to 0.08 K in magnetic fields of B ≤ 12 T. The 4f contribution to the specific heat divided by temperature C4f/T diverges as −lnT in B = 0 and 2 T applied along the [100] direction. In B = 4 T, however, C4f(T) exhibits a broad maximum, which shifts to higher temperatures with increasing B. This behavior can be explained by the Zeeman effect which splits the ground state doublet through the first excited triplet. The 4f contribution to the entropy, S4f(T), in B ≥ 4 T is well reproduced by the crystalline electric field calculation, whereas the calculation fails to reproduce the S4f(T) data in B ≤ 2 T. We propose that the on-site interaction of the active quadrupole in the ground state doublet with two-channel conduction bands gives rise to the –lnT variation of C4f/T.

System Y

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.

_{1-x}

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.

Pr

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.