T. Mihalisin

Resistive behavior and intermediate valence effects in La1−xCexPd3 and CePd3−xRhx

The electrical resistivity of CePd3, La1−xCexPd3, CeRhxPd3−x and Ce Pd3+x systems has been measured from helium temperature to 300 K. The resistivity of pure CePd3 rises from 125 μ Ω cm to 150 μ Ω cm as one cools from 300 K to 100 K. Below 100 K the resisitivity drops dramatically to 10 μ Ω cm at low temperatures. The same qualitative behavior, though less pronounced, is observed in other systems such as CeSn3 which like CePd3 are believed to be of intermediate valence. For x<0.3 the system La1−xCexPd3 is believed to be trivalent. We observe Kondo‐like behavior in this regime. For x near unity we observe that extremely small amounts of La eliminate the rapid fall in resistivity observed below 100 K for pure CePd3. These results suggest that this fall off is due to some type of cooperative Ce ion hehavior. The CeRhxPd3−x system allows one to monitor the effect on resistivity of varying the Ce valence from 3.45 in CePd3 to 4 in CeRh.64Pd2.36. We find that the magnitude of the resistivity rise (upon cooling ...

Magnetic ordering in M(ox)(bpy) system (M=Fe, Co, Ni; ox=C2O42−; bpy=4,4′-bipyridine)

The temperature and field dependence of the magnetization have been measured to investigate the magnetic properties of the first oxalate–bpy mixed-ligand framework with a general formula M(ox)(bpy) (M = Fe(II), Co(II), Ni(II); ox = C2O42−; bpy = 4,4′-bipyridine). All compounds in the M(ox)(bpy) system crystallize in an orthorhombic structure with space group Immm (No. 71), in which the magnetic M ions form one-dimensional chains along the a axis. Spontaneous magnetic orderings with transition temperatures of 12, 13, and 26 K have been found for Fe(ox)(bpy), Co(ox)(bpy), and Ni(ox)(bpy), respectively. The nature of the ordering in Ni(ox)(bpy) is antiferromagnetic, however it may exhibit a metamagnetic transition at high magnetic fields. The type of ordering in Fe(ox)(bpy) and Co(ox)(bpy) is also antiferromagnetic but with canting, or so-called weak ferromagnetism. The residual moment resulting from the canting is larger in Fe(ox)(bpy) than in Co(ox)(bpy). The values of μeff obtained by fitting χ(T) indicat...

CeSn3, a strongly mixed valent material

Abstract Ce in CeIn 3− x Sn x is found to be trivalent for x x > 1.8. In the mixed valence regime, specific heat, susceptibility and resistivity depend on the number of f electrons, n f , in the manner prescribed by recent theories but only if n f = 0.4 for pure CeSn 3 .

Kondo scattering from Sm ions in La1−xSmxSn3☆

Abstract We report here clear evidence for Kondo scattering from a rare earth ion which is free from the usual complications of crystalline electric field splittings and valence fluctuations.

Magnetic and thermodynamic properties of nonsuperconducting (Y,Pr)Ba2Cu3O6

The concentration dependence of the room‐temperature lattice constants and the concentration and temperature dependence of the specific heat C(T) and the magnetic susceptibility have been measured on the tetragonal, nonsuperconducting phase of Y1−xPrxBa2Cu3O6. The effective paramagnetic moment μeff is independent of x and has an average value of 2.7±0.2 μB. For PrBa2Cu3O6, the Neel temperature TN for Pr moment ordering is 10.5 K as compared to TN=17 K for the orthorhombic PrBa2Cu3O7 phase. The TN is depressed rapidly with Y doping in the oxygen‐depleted compound and goes to zero at x≊0.4–0.5. At low temperatures and x≤0.5, C(T)/T vs T2 is nonlinear and shows a rapid decrease of C(T)/T indicative of strong magnetic correlations.

The influence of finite size on critical phenomena in Ni films

Abstract The depression of Tc for Ni films is found to be proportional to n−λ where n is the number of atomic layers and λ = 1.33±0.13. This suggests that λ may equal 1 v where v is the correlation length exponent.

Coefficient of thermal expansion and critical behavior of TGS

Abstract New measurements of the coefficient of thermal expansion, α, above the T c of tri-glycine-sulfate (TGS) demonstrate the presence of a logarithmic anomaly in α, in agreement with the generalized Pippard relations between the previously measured specific heat and α.

Superconductivity and structural transformation in HfV2 and Nb‐doped HfV2

The temperature dependence of the specific heat shows that the strong electron‐phonon coupling system HfV2 undergoes a structural transformation at 116 K and becomes superconducting around 9 K. The structural instability can be interpreted in terms of a strong electron‐phonon coupling and Fermi surface nesting. The structural transformation shifts to lower temperatures with very dilute Nb substitution in HfV2, and completely disappears with only 5 at. % Nb. The low‐temperature specific heat of HfV2 shows a large density of states at the Fermi level. These experimental results are consistent with predictions from band‐structure calculations.

LIII absorption, resistivity, and susceptibility studies of the Ce(Ni1−xCox)2 and Y(Ni1−xCox)2 systems

We have measured the valence of Ce in Ce(Ni1−xCox)2 by LIII absorption and find that it is constant at 3.20±0.02. However, striking variations in the resistive behavior are seen across this series. Even more pronounced variation in resistive behavior, as well as, large changes in the susceptibility are seen in the Y(Ni1−xCox)2 system. It is argued that d electron spin fluctuations may be responsible for the observed behavior in both systems.

LIII absorption studies of the mixed valence systems Ce(Rh1−xRux)2 and Ce(Rh1−yPty)2

The valence of Ce in Ce(Rh1−xRux)2 and Ce(Rh1−yPty)2 has been measured by LIII absorption. The valence of Ce is constant at 3.0 for Ce(Rh1−yPty)2 samples from CePt2 to Ce(Rh0.5Pt0.5)2, then varies smoothly to 3.13 at CeRh2 and 3.20 at CeRu2. The lattice constants for this system have also been measured. Ce valences inferred from Vegard’s law are compared to the LIII determined values.