No abstract

Based on low temperature resistivity, heat capacity and magnetization investigations we show that the unusually strong suppression of superconductivity in LuxZr1−xB12 BSC-type superconductors in the range x<0.08 is caused by the emergence of static spin polarization in the vicinity of nonmagnetic lutetium impurities. The analysis of received results points to a formation of static magnetic moments with µ ef f ≈3µB per Lu-ion. The size of these spin polarized nanodomains was estimated to be about 5Å.

Electron spin resonance (ESR) in strongly correlated metals is an exciting phenomenon, as strong spin fluctuations in this class of materials broaden extremely the absorption line below the detection limit. In this respect, ESR observation in CeB6 provides a unique chance to inspect Ce3+ magnetic state in the antiferroquadrupole (AFQ) phase. We apply the original high frequency (60 GHz) experimental technique to extract the temperature and angular dependences of g-factor, line width and oscillating magnetization. Experimental data show unambiguously that the modern ESR theory in the AFQ phase considering the Γ8 ground state of Ce3+ ion completely fails to predict both the g-factor magnitude and its angular dependence. Alignment of the external magnetic field along [100] axis induces a strong (more than twofold) broadening of ESR line width with respect to the other crystallographic directions and results also in the anomalous temperature dependences of the g-factor and oscillating magnetization. In this experimental geometry the latter parameter surprisingly exceeds total static magnetization by 20% at T* ~ 2.5 K. We argue that the unusual physical picture of ESR in CeB6 may be strongly affected by spin fluctuations and dynamic collective effects predominantly pronounced in [100] direction.

No abstract

Introducing of topological insulator concept for fluctuating valence compound – samarium hexaboride – has recently initiated a new round of studies aimed to clarify the nature of the ground state in this extraordinary system with strong electron correlations. Here we discuss the data of magnetic resonance in the pristine single crystals of SmB6 measured in 60 GHz cavity experiments at temperatures 1.8–300 K. The microwave study as well as the DC resistivity and Hall effect measurements performed for the different states of SmB6 [110] surface prove definitely the existence of the layer with metallic conductivity increasing under lowering temperature below 5 K. Four lines with the g-factors g ≈ 2 are found to contribute to the ESR-like absorption spectrum that may be attributed to intrinsic paramagnetic centers on the sample’s surface, which are robust with respect to the surface treatment. The temperature dependence of integrated intensity I(T) for main paramagnetic signal is found to demonstrate anomalous critical behavior I(T) ~ (T* − T)ν with characteristic temperature T* = 5.34 ± 0.05 K and exponent ν = 0.38 ± 0.03 indicating possible magnetic transition at the SmB6 [110] surface. Additional resonant magnetoabsorption line, which may be associated with either donor-like defects or cyclotron resonance mode corresponding to the mass mc ~ 1.2m0, is reported.

Angular dependences of ESR line parameters (g-factor and linewidth ∆H) were experimentally explored in the antiferroquadrupolar phase of heavy fermion system CeB6 at T = 1.8 K. The data were obtained in two experimental geometries with different mutual directions of the wavevector k and the external magnetic field H at frequency of f = 60 GHz. A g-factor anisotropy was found: while g-factors for [110] and [111] directions are close to each other (g ≈ 1.6), it is considerably higher (g ≈ 1.75) for [100]. The obtained angular dependence g(Θ) was compared with the theoretically predicted g-factor behavior for the Γ8 state of Ce 3+ ion in antiferroquadrupolar phase of CeB6. It turns out that the experimental g-factor is considerably smaller at all angles than the theoretically calculated limits (2 < g < 2.2) and, moreover, it has a different symmetry. This result together with the strong linewidth anisotropy ∆H(Θ) demonstrates that for the relevant description of experimental data the theoretical model should take into account also the interaction of Ce 3+ ion with itinerant 5d electrons.

No abstract

No abstract