Observation of a phase transition at 55 K in single-crystal CaCu1.7As2

Abstract

We present the structural, magnetic, thermal and ab-plane electronic transport properties of single crystals of CaCu1.7As2 grown by the self-flux technique that were investigated by powder x-ray diffraction, magnetic susceptibility χ, isothermal magnetization M , specific heat Cp, and electrical resistivity ρ measurements as a function of temperature T and magnetic field H. X-ray diffraction analysis of crushed crystals at room temperature confirm the collapsed tetragonal ThCr2Si2-type structure with ∼ 15% vacancies on the Cu sites as previously reported, corresponding to the composition CaCu1.7As2. The χ(T ) data are diamagnetic, anisotropic and nearly independent of T . The χ is larger in the ab-plane than along the c-axis, as also observed previously for SrCu2As2 and for pure and doped BaFe2As2. The Cp(T ) and ρ(T ) data indicate metallic sp-band character. In contrast to the χ(T ) and Cp(T ) data that do not show any evidence for phase transitions below 300 K, the ρ(T ) data exhibit a sharp decrease on cooling below a temperature Tt = 54-56 K, depending on the crystal. The ρ(T ) data show no hysteresis on warming and cooling through Tt and the transition thus appears to be second order. The phase transition may arise from spatial ordering of the vacancies on the Cu sublattice. The Tt is found to be independent of H for H ≤ 8 T. A positive magnetoresistance is observed below Tt that increases with decreasing T and attains a value in H = 8.0 T of 8.7% at T = 1.8 K.

Superconducting and normal-state properties ofAPd2As2(AAnand1, Kim2, Tanatar3 et al. 2013Phys. Rev. BSelf Cite665920View full textAdd to dashboardCite

“…The extent and effects of electron and hole doping by such substitutions are still being debated. 12,31,37,[39][40][41] While the effect of partial substitutions of Fe by transition metals have been investigated extensively, the physical properties of the end-point compounds AM 2 As 2 of the A(Fe 1−x M x ) 2 As 2 series are often not known in detail. Recently we reported crystallography and physical property studies of the end-point compounds SrCu 2 As 2 and CaCu 1.7 As 2 for M = Cu which are sp-band metals.…”

Crystallography and physical properties ofBaCo2As2,Ba0.94K0.06Anand1, Quirinale2, Lee3 et al. 2014Phys. Rev. BSelf Cite396440View full textAdd to dashboardCite

“…22) and CaCu 1.7 As 2 exhibit sp-band metallic behavior with a phase transition at 55 K in CaCu 1.7 As 2 (Refs. 23,24) that may arise from ordering of the Cu vacancies. 24 Bulk s-wave superconductivity below T c = 1.27 and 0.92 K occurs in CaPd 2 As 2 and SrPd 2 As 2 , respectively, 25 and below T c = 1.69 and 3.04 K in the related compounds CaPd 2 Ge 2 (Ref.…”

“…23,24) that may arise from ordering of the Cu vacancies. 24 Bulk s-wave superconductivity below T c = 1.27 and 0.92 K occurs in CaPd 2 As 2 and SrPd 2 As 2 , respectively, 25 and below T c = 1.69 and 3.04 K in the related compounds CaPd 2 Ge 2 (Ref. 26) and SrPd 2 Ge 2 , 27 respectively.…”

Metallic behavior induced by potassium doping of the trigonal antiferromagnetic insulatorEuMn2As2

“…Continuing our work on 122-type pnictides in the search for novel properties and ground states [24][25][26][27][28][29][30][31], here we report a comprehensive investigation of the physical properties of EuMn 2 As 2 which crystallizes in the trigonal CaAl 2 Si 2 -type structure (space group P3m1) [32]. This structure is quite different from the common body-centered tetragonal ThCr 2 Si 2 -type structure of 122 compounds [33].…”