B. Elschner

Gd3+-ESR in the intermediate valent cerium alloys Ce1−xYxPd3, Ce(Pd1−xRhx)3 and Ce(Pd1−xAgx)3

In the intermediate valent cerium alloys Ce1−xYxPd3, Ce(Pd1−xRhx)3 and Ce(Pd1−xAgx)3 the Gd3+-ESR shows a non-linear increase of the linewidth ΔH(T) in the temperature range 4.2K≦T≦300K. The deviation from the linear Korringa law can be described by a reduced conduction electron density of states at the Gd site (which is a Ce lattice site) in the energy range ΔE4f (=width of the Ce 4f states). This supposition allows a determination of ΔE4f from the ΔH(T)-data. For CePd3:Gd3+ we find ΔE4f=(650±100) K. ΔE4f increases with Y- and Rh-concentration and decreases with Ag-concentration.

Influence of Ce spin fluctuations on the Gd ESR in Y1−xCexAl2

The Gd ESR and magnetic susceptibility of Y1−xCexAl2 (0.01≦x≦1) were measured in the temperature range 1.5–25 K (ESR) and 2.6–290 K (χ), respectively. The Gd ESR spectrum is substantially altered in the presence of Ce ions. The Gd resonance linewidth shows a non-linear temperature dependence which is more pronounced for higher Ce concentrations. A model is suggested to explain the linewidth behaviour and to estimate the spin fluctuation time of Ce ions in this system.

ESR of Gd-impurities in the heavy fermion compounds CeCu2Si2 and CeAl3

The heavy fermion systems CeCu2Si2 and CeAl3 are characterized by a huge quasiparticle density of states responsible for the large electronic specific heat. The observation of a Gd3+ electron spin resonance (ESR) in single crystals CeCu2Si2 and in polycrystalline CeAl3 clearly demonstrates the local character of these quasiparticles. Nevertheless, the Gd-spin relaxation shows remarkable anomalies with respect to the isostructural compounds LaCu2Si2 and LaAl3: Probably via RKKY coupling, Ce 4f-spin fluctuations give rise to an enhanced Gd-spin relaxation resulting in an unusual non-linear thermal broadening around the Kondo temperature. From this we obtain information about the temperature dependence of the Ce 4f-spin correlation time.

Gd3+-ESR in the intermediate valent cerium compounds Ce x La1-xOs2

In the intermediate valent compounds CexLa1−xOs2 the Gd3+-ESR shows a non-linear increase of the linewidth ΔH(T) in the temperature range 4.2K<T<300K for 0.3≦x≦1.0. This non-linearity of the thermal broadening is strongly altered by changing the Ce-concentration. The experimental results ΔH(T,x) can quantitatively be described via hybridization of conduction electrons with Ce4f electrons: Due to hybridization, the Ce4f states are broadened but remain localized. The conduction electron density of states is reduced in the vicinity of the 4f states. In addition we observe a maximum in the electrical resistivity ϱ(T) of CeOs2 at 270 K.

Possible 4f7 5d1 Ground State of Gd Impurities in the Mixed-Valence Compound SmB6, Observed with Electron Spin Resonance

In SmB6 single crystals we observe a very anomalous ESR spectrum of Gd below 5 K. As far as we know, this is the first Gd spectrum, which cannot be explained by the electronic configuration Gd3+ 4f7. We discuss the appearance of the anomalous spectrum below 5 K by a trapped conduction electron, forming a formal divalent Gd 4f7 5d1 ground state. Above 6 K, where the conduction band of SmB6 becomes populated, we observe the usual Gd3+ Dysonian resonance as in conventional metals. The Hamiltonian of the 4f7 5d1 configuration, including a dynamic Jahn-Teller effect of the 5d electron, describes the complicated Gd spectrum reasonably well. The question, why SmB6, until now, seems to be the only host in which Gd3+ attracts a further electron, remains open.

Metal-Insulator Transition in Ytterbium Under Pressure: an EPR Study

We study the pressure-induced metal-insulator (MI) transition in ytterbium using EPR measurements with Eu as the probe for magnetic resonance. For a given pressure the linewidth ΔH increases linearly with temperature indicating a Korringa type of relaxation of the Eu impurities by the conduction electrons of the host. With increasing pressure dΔH/dT decreases becoming very small at a critical pressure Pc ≈ 12.5 kbars. Close to Pc, dΔH/dT decreases linearly with (P - Pc) in agreement with the scaling theory for density-driven metal-insulator transitions. To the best of our knowledge, this is the first time such transitions are studied by magnetic resonance.

Spin dynamics in La2−xSrxCuO4+δ probed by electron paramagnetic resonance

Abstract We report on EPR experiments on single crystals of La 2− x Sr x CuO 4+δ for Sr-concentrations 0.07 ⩽ x ⩽ 0.20. Intrinsic EPR signals have been observed for all concentrations. The anomalous temperature dependence of the g -shift and of the line width are explained in terms of a strong coupling of the EPR probe to the spin fluctuations in the CuO 2 planes.

Cu-EPR in YBa2Cu3O6+δ single crystals

We report on the observation of Cu-EPR signals in single crystalline material of YBa2Cu3O6+δ in the narrow oxygen concentration range 0.7<δ<0.9 and for temperatures 80 K<T<200 K. We provide evidence that the signal results from Cu2+ ions located in ⋯Cu(1)⋯O⋯Cu(1)⋯ chain fragments.

ESR studies of magnetic state evolution at the phase transition in Yb0.5In0.5Cu2

Abstract The ESR of the Gd+3 ion was investigated in Yb0.5In0.5Cu2 at temperatures below and above the first-order phase transition which occurs in this material at Tp ∼ 50 K. We present arguments that this compound is in a Kondo state that varies with the temperature and that the phase transition is connected with the change in the Yb+3 volume due to the “Kondo-collapse” mechanism.

Paramagnetic resonance in CeAl3:Gd under hydrostatic pressure

We present ESR-data for Gd3+-impurities in the heavy fermion compound CeAl3 under hydrostatic pressure up to 17kbar. At ambient pressure andT<4K the Gd-resonance shows a strongly enhanced thermal broadening with respect to isostructural LaAl3. With increasing pressure this slope decreases from at least 138 Oe/K (p=0) to 18 Oe/K (p=17kbar) which is almost the Korringa slope of LaAl3. These results support the idea of an increasing Ce-spin fluctuation rate as a function of pressure.