Crystallographic, electronic, thermal, and magnetic properties of single-crystal SrCo2As2

Abstract

In tetragonal SrCo2As2 single crystals, inelastic neutron scattering measurements demonstrated that strong stripe-type antiferromagnetic (AFM) correlations occur at a temperature T = 5 K [W. Jayasekara et al., arXiv:1306.5174] that are the same as in the isostructural AFe2As2 (A = Ca, Sr, Ba) parent compounds of high-Tc superconductors. This surprising discovery suggests that SrCo2As2 may also be a good parent compound for high-Tc superconductivity. Here, structural and thermal expansion, electrical resistivity ρ, angle-resolved photoemission spectroscopy (ARPES), heat capacity Cp, magnetic susceptibility χ, 75 As NMR and neutron diffraction measurements of SrCo2As2 crystals are reported together with LDA band structure calculations that shed further light on this fascinating material. The c-axis thermal expansion coefficient αc is negative from 7 to 300 K, whereas αa (the a-axis thermal expansion coefficient) is positive over this T range. The ρ(T ) shows metallic character. The ARPES measurements and band theory confirm the metallic character and in addition show the presence of a flat band near the Fermi energy EF. The band calculations exhibit an extremely sharp peak in the density of states D(E ≈ EF) arising from a flat d x 2 −y 2 band, where the x and y axes are along the a and b axes of the Co square lattice, respectively. A comparison of the Sommerfeld coefficient of the electronic specific heat with χ(T → 0) suggests the presence of strong ferromagnetic itinerant spin correlations which on the basis of the Stoner criterion predicts that SrCo2As2 should be an itinerant ferromagnet, in conflict with the magnetization data. The χ(T ) does have a large magnitude, but also exhibits a broad maximum at ≈ 115 K suggestive of dynamic short-range AFM spin correlations, in agreement with the neutron scattering data. The measurements show no evidence for any type of phase transition between 1.3 and 300 K and we suggest that metallic SrCo2As2 has a gapless quantum spin-liquid ground state.

Low-temperature nuclear magnetic resonance investigation of systems frustrated by competing exchange interactions

“…Thus we conclude that strong AFM spin fluctuations are realized in the HT T phase in both the "annealed" and "as-grown" CaFe 2 As 2 crystals, consistent with INS measurements On the contrary since we do not observe any signature of AFM correlations in LT c−T phase either from the T dependence of 1/T 1 T χ or from the NMR spectrum, we conclude that electron correlations melt in this phase. This is consistent with inelastic neutron scattering measurements [173][186] and with the results of ARPES [190], both of which demonstrate the evidence of the absence of magnetic fluctuations in the nonsuperconducting c−T phase in CaFe 2 As 2 .…”

“…Orbital ordering has been held responsible for the strong anisotropy in the exchange interaction. [68]. Another possibility was the effect of a higher-order [biquadratic ( S i · S i ) 2 ] term in the Hamiltonian [69] which also favors stripe AFM ordering.…”

Anomalous Composition-Induced Crossover in the Magnetic Properties of the Itinerant-Electron AntiferromagnetCa1−xSrxCo2−yAs2Sangeetha1, Smetana2, Mudring3 et al. 2017Phys. Rev. Lett.213540View full textAdd to dashboardCite

“…The data for SrCo2As2 are room-temperature data taken from Ref. [32]. The compositions in the first column except for SrCo2As2 were all obtained from combined EDS and single-crystal XRD analyses.…”

“…Spin-flop transitions in single crystals of CaCo 2−y As 2 with the magnetic field H applied parallel to the c axis occur at H SF ∼ 3.5-3.7 T [25,26,30,31]. On the other hand, metallic SrCo 2 As 2 exhibits no magnetic transitions versus T [32]. However, single-crystal χ(T ) data for both c-axis and ab-plane magnetic field alignments show broad maxima at T ≈ 115 K, suggesting the presence of dynamic AFM correlations.…”

Ba0.4Rb0.6Mn2As2: A prototype half-metallic ferromagnet

“…As a result, new 1111-type superconductors were discovered, together with other superconductors with related 11-, 111-, 122-type and other structures [2][3][4] . While most of the investigations in the field were centered around FeAs-based compounds, work was also carried out to extend the search for superconductivity and other exotic ground states to isostructural compounds where iron was competely replaced by another transition metal [5][6][7][8] . BaMn 2 As 2 is one such compound that has been extensively investigated 5,6,9 .…”