Remarkably robust and correlated coherence and antiferromagnetism in (Ce1−x_{1-x}Lax_x)Cu2_2Ge2_2

We present magnetic susceptibility, resistivity, specific heat, and thermoelectric power measurements on (Ce$_{1-x}$La$_x$)Cu$_2$Ge$_2$ single crystals (0 $\leq x\leq$ 1). With La substitution, the antiferromagnetic temperature $T_N$ is suppressed in an almost linear fashion and moves below 0.36 K, the base temperature of our measurements for $x>$ 0.8. Surprisingly, in addition to robust antiferromagnetism, the system also shows low temperature coherent scattering below $T_{coh}$ up to $\sim$ 0.9 of La, indicating a small percolation limit $\sim$ 9$\%$ of Ce that separates a coherent regime from a single-ion Kondo impurity regime. $T_{coh}$ as a function of magnetic field was found to have different behavior for $x$ 0.9. Remarkably, $(T_{coh})^2$ at $H$ = 0 was found to be linearly proportional to $T_N$. The jump in the magnetic specific heat $\delta C_{m}$ at $T_N$ as a function of $T_K/T_N$ for (Ce$_{1-x}$La$_x$)Cu$_2$Ge$_2$ follows the theoretical prediction based on the molecular field calculation for the $S$ = 1/2 resonant level model

57-Fe Mossbauer study of magnetic ordering in superconducting K_0.85Fe_1.83Se_2.09 single crystals

The magnetic ordering of superconducting single crystals of K_0.85Fe_1.83Se_2.09 has been studied between 10K and 550K using 57-Fe Mossbauer spectroscopy. Despite being superconducting below T_sc ~30K, the iron sublattice in K_0.85Fe_1.83Se_2.09 clearly exhibits magnetic order from well below T_sc to its N\'eel temperature of T_N = 532 +/- 2K. The iron moments are ordered perpendicular to the single crystal plates, i.e. parallel to the crystal c-axis. The order collapses rapidly above 500K and the accompanying growth of a paramagnetic component suggests that the magnetic transition may be first order, which may explain the unusual temperature dependence reported in recent neutron diffraction studies.Comment: 6 pages, 4 figures Submitted to Phys.Rev.

Mounting Materials for Automated Image Analysis of Coals Using Backscattered Electron Imaging

In order to apply SEM-based automated image analysis (AIA) to the characterization of not only minerals in coal but to the coal itself, sample preparation methods need to be developed beyond common practice. A significant consideration is the degree of contrast achievable between the mount media chosen and the coal. Four low-atomic number materials (epoxy, polyethylene, polystyrene and carnauba wax) were compared for their potential as suitable mounting media for coal samples. Epoxy is satisfactory only for characterization of mineral particles since the contrast between epoxy and coal particles is negligible. Polyethylene or polystyrene have marginal application for use as mounting material for coal characterization due to limited contrast and sample preparation artifacts. Carnauba wax appears satisfactory as a mounting material since it provides good contrast with coal particles with minimal artifacts

Doping - dependent superconducting gap anisotropy in the two-dimensional 10-3-8 pnictide Ca10_{10}(Pt3_3As8_8)[(Fe1−x_{1-x}Ptx_{x})2_2As2_2]5_5

The characteristic features of Ca$_{10}$(Pt$_3$As$_8$)[(Fe$_{1-x}$Pt$_x$)$_2$As$_2$]$_5$ ("10-3-8") superconductor are relatively high anisotropy and a clear separation of superconductivity and structural/magnetic transitions, which allows studying the superconducting gap without complications due to the coexisting order parameters. The London penetration depth, measured in underdoped single crystals of 10-3-8 ($x =$ 0.028, 0.041, 0.042, and 0.097), shows behavior remarkably similar to other Fe-based superconductors, exhibiting robust power-law, $\Delta \lambda(T) = A T^n$. The exponent $n$ decreases from 2.36 ($x =$ 0.097, close to optimal doping) to 1.7 ($x =$ 0.028, a heavily underdoped composition), suggesting that the superconducting gap becomes more anisotropic at the dome edge. A similar trend is found in low-anisotropy superconductors based on BaFe$_2$As$_2$ ("122"), implying that it is an intrinsic property of superconductivity in iron pnictides, unrelated to the coexistence of magnetic order and superconductivity or the anisotropy of the normal state. Overall this doping dependence is consistent with $s_{\pm}$ pairing competing with intra-band repulsion

Synthesis and characterization of Ca-doped LaMnAsO

We report on our attempt to hole-dope the antiferromagnetic semiconductor LaMnAsO by substitution of the La3+ site by Ca2+. We use neutron and x-ray diffraction, magnetic susceptibility, and transport techniques to characterize polycrystalline (La1−xCax)MnAsO samples prepared by solid-state reaction and find that the parent compound is highly resistant to substitution with an upper limit x≤0.01. Magnetic susceptibility of the parent and the x=0.002(xnom=0.04) compounds indicate a negligible presence of magnetic impurities (i.e., MnO or MnAs). Rietveld analysis of neutron and x-ray diffraction data shows the preservation of both the tetragonal (P4/nmm) structure upon doping and the antiferromagnetic ordering temperature, TN=355±5 K