Intense efforts have been made in order to synthesize new tetragonal ternary intermetallic compounds with low-temperature ground states on the border of magnetism. Here we report the synthesis of ThCo2Sn2 single crystals, which crystallize in the tetragonal CaBe2Ge2-type structure, using the flux technique. Further investigation of the physical properties by magnetic susceptibility and pressure-dependent electrical resistivity measurements confirm the presence of antiferromagnetic ordering associated with the Co ions, but with a higher ordering temperature of TN 78 K when compared to TN 65 K of the polycrystalline counterpart. Our results show that both Cu-substitution and applied pressure up to 22 kbar are not able to induce superconductivity in this system. Nevertheless, our analyses point out to a putative quantum critical point at higher pressures.

Single crystals of Ba 1-xEu xFe 2As 2 were studied by magnetic susceptibility, heat capacity, resistivity, and electron spin resonance (ESR) measurements. Spin-density wave (at T SDW) and antiferromagnetic (at T N) phase transitions were mapped as a function of x. For 0.2, we found a single Eu2 + ESR Dysonian line that presents an isotropic linear increase (Korringa) of its linewidth (ΔH) above T SDW which systematically decreases with decreasing x. In contrast, for a critical concentration x c (0.10

We report a combined study of hydrostatic pressure (P ≤ 25 kbar) and chemical substitution on the magnetic pair-breaking effect in Eu- and Mn-substituted BaFe2As2 single crystals. At ambient pressure, both substitutions suppress the superconducting (SC) transition temperature (Tc) of BaFe2–xCoxAs2 samples slightly under the optimally doped region, indicating the presence of a pair-breaking effect. At low pressures, an increase of Tc is observed for all studied compounds followed by an expected decrease at higher pressures. However, in the Eu dilute system, Tc further increases at higher pressure along with a narrowing of the SC transition, suggesting that a pair-breaking mechanism reminiscent of the Eu Kondo single impurity regime is being suppressed by pressure. Furthermore, Electron Spin Resonance (ESR) measurements indicate the presence of Mn2+ and Eu2+ local moments and the microscopic parameters extracted from the ESR analysis reveal that the Abrikosov–Gor'kov expression for magnetic pair-breaking in a conventional sign-preserving superconducting state cannot describe the observed reduction of Tc.

We present electron spin resonance (ESR) measurements in single-crystalline samples of EuIn 2As 2 grown using the In-flux method. This compound crystallizes in a hexagonal P6(3)/mmc structure and presents antiferromagnetic (AFM) ordering below T N=16 K. In the paramagnetic state, a single Eu2 + Dysonian ESR line with nearly temperature-independent g-factor and linewidth is observed, indicating the absence of Korringa-like relaxation of the Eu2 + ions. Approaching the AFM transition, we observe an anisotropic g-shift and a linewidth broadening which has a maximum at T N, suggesting that the short-range AFM correlation dominates the spin dynamics of the Eu2 + spins in this temperature range. Our results are discussed based on complementary data (magnetic susceptibility, heat capacity, and electrical resistivity measurements) that provide further details about the global macroscopic physical properties of the EuIn 2As 2 intermetallic compound. © 2012 American Physical Society.

Bi2Se3 has been claimed to be a three dimensional topological insulator (TI) with topologically protected metallic surface states with exotic properties. We have performed electron spin resonance (ESR) measurements on Gd3+ doped (x ≈ 0.01) Bi2Se3 single crystal grown from stoichiometric melt. For the studied crystals, our preliminary results revealed a partly resolved Gd3+ fine structure spectrum with Dysonian (metallic character) lines. At room temperature, the central line has a g ≈ 1.98, a linewidth ΔH ≈ 95 G and the spectra have a overall splitting of roughly 1300 Oe. As the temperature is decreased, the Gd3+ ESR ΔH of the central line presents a very small Korringa-like behavior b =ΔH/ΔT ≈ 0.013 Oe/K and nearly T-independent g-value. However, for T ≲ 40 K, ΔH shows a stronger narrowing effect evolving to Korringa-like behavior (b ≈ 0.15 Oe/K) for T ≲ 30 K. Concomitantly with the change in ΔH behavior, the Gd3+ central line g value starts to decrease reaching a value of 1.976 at T =4.2 K. The ESR results are discussed in terms of possible effects of protected topological surface states enlightened by complementary data from macroscopic measurements.

The role of orbital differentiation on the emergence of superconductivity in the Fe-based superconductors remains an open question to the scientific community. In this investigation, we employ a suitable microscopic spin probe technique, namely Electron Spin Resonance (ESR), to investigate this issue on selected chemically substituted BaFe2As2 single crystals. As the spin-density wave (SDW) phase is suppressed, we observe a clear increase of the Fe 3d bands anisotropy along with their localization at the FeAs plane. Such an increase of the planar orbital content is interestingly independent of the chemical substitution responsible for suppressing the SDW phase. As a consequence, the magnetic fluctuations in combination with this particular symmetry of the Fe 3d bands are propitious ingredients for the emergence of superconductivity in this class of materials.

Electron spin resonance (ESR) of diluted Nd(3+) ions in the topologically nontrivial semimetallic (TNSM) YBiPt compound is reported. The cubic YBiPt compound is a non-centrosymmetric half Heusler material which crystallizes in the F43m space group. The low temperature Nd(3+) ESR spectra showed a g-value of 2.66(4) corresponding to a Γ6 cubic crystal field Kramers' doublet ground state. Remarkably, the observed metallic and diffusive (Dysonian) Nd(3+) lineshape presented an unusual dependence with grain size, microwave power, Nd(3+) concentration and temperature. Moreover, the spin dynamic of the localized Nd(3+) ions in YBiPt was found to be characteristic of a phonon-bottleneck regime. It is claimed that, in this regime for YBiPt, phonons are responsible for mediating the diffusion of the microwave energy absorbed at resonance by the Nd(3+) ions to the thermal bath throughout the skin depth (δ ≃ μm). We argue that this is only possible because of the existence of highly mobile conduction electrons inside the skin depth of YBiPt that are strongly coupled to the phonons by spin-orbit coupling. Therefore, our unexpected ESR results point to a coexistence of metallic and insulating behaviors within the skin depth of YBiPt. This scenario is discussed in the light of the TNSM properties of this compound.

Quantum oscillation measurements provide relevant information about the Fermi surface (FS) properties of strongly correlated metals. Here, we report on the Shubnikov-de Haas effect via high-field resistivity measurements of EuFe2As2 (Eu122) and BaFe2As2 (Ba122) single crystals. Although both pnictide compounds are isovalent with similar effective masses and density of states, at the Fermi level, our results reveal subtle changes in their fermiology. Remarkably, although the spin-density-wave (SDW) ordering temperature is higher in the Eu-rich end, Eu122 displays a much more isotropic and three-dimensional-like FS when compared with Ba122, in agreement with band structure calculations. Our experimental results suggest an anisotropic contribution of the Fe 3d orbitals to the FS in Ba122. We speculate that this orbital differentiation may be responsible for the suppression of the SDW phase in the FeAs-based compounds.

The possible existence of a sign-changing gap symmetry in BaFe2As2-derived superconductors (SC) has been an exciting topic of research in the last few years. To further investigate this subject we combine Electron Spin Resonance (ESR) and pressure-dependent transport measurements to investigate magnetic pair-breaking effects on BaFe1.9M0.1As2 (M = Mn, Co, Cu, and Ni) single crystals. An ESR signal, indicative of the presence of localized magnetic moments, is observed only for M = Cu and Mn compounds, which display very low SC transition temperature (Tc) and no SC, respectively. From the ESR analysis assuming the absence of bottleneck effects, the microscopic parameters are extracted to show that this reduction of Tc cannot be accounted by the Abrikosov-Gorkov pair-breaking expression for a sign-preserving gap function. Our results reveal an unconventional spin- and pressure-dependent pair-breaking effect and impose strong constraints on the pairing symmetry of these materials.

In this work we combine magnetization, pressure dependent electrical resistivity, heat capacity, Cu63 nuclear magnetic resonance (NMR), and x-ray resonant magnetic scattering experiments to investigate the physical properties of the intermetallic CeCuBi2 compound. Our single crystals show an antiferromagnetic ordering at TN≃16 K and the magnetic properties indicate that this compound is an Ising antiferromagnet. In particular, the low temperature magnetization data revealed a spin-flop transition at T=5 K when magnetic fields of about 5.5 T are applied along the c axis. Moreover, the x-ray magnetic diffraction data below TN revealed a commensurate antiferromagnetic structure with propagation wave vector (0012) with the Ce3+ moments oriented along the c axis. Furthermore, our heat capacity, pressure dependent resistivity, and temperature dependent Cu63 NMR data suggest that CeCuBi2 exhibits a weak heavy fermion behavior with strongly localized Ce3+ 4f electrons. We thus discuss a scenario in which both the anisotropic magnetic interactions between the Ce3+ ions and the tetragonal crystalline electric field effects are taking into account in CeCuBi2.