2016/06/30 by V. K. Anand, D. C. Johnston · 2 citations
Physics and Astronomy · #cond-mat.mtrl-sci #cond-mat.str-el
paper · pdf · doi:10.1103/physrevb.94.014431
published as Phys. Rev. B 94, 014431 (2016); 19 pages · 21 pages, 22 figures, 4 Tables
arxiv created 2016/08/09 · arxiv updated 2016/12/13
We report magnetic susceptibility χ, isothermal magnetization M, heat capacity Cp and electrical resistivity ρmeasurements on undoped EuMn2As2 and K-doped Eu0.96K0.04Mn2As2 and Eu0.93K0.07Mn2As2 single crystals with the trigonal CaAl2Si2-type structure as a function of temperature T and magnetic field H. EuMn2As2 has an insulating ground state with an activation energy of 52 meV and exhibits antiferromagnetic (AFM) ordering of the Eu+2 spins S=7/2 at TN1 = 15 K from Cp(T) and χ(T) data with a likely spin-reorientation transition at TN2 = 5.0 K. The Mn+2 3d5 spins-5/2 exhibit AFM ordering at TN = 142 K from all three types of measurements. The M(H) isotherm and χ(T) data indicate that the Eu AFM structure is both noncollinear and noncoplanar. The AFM structure of the Mn spins is also unclear. A 4% substitution of K for Eu in Eu0.96K0.04Mn2As2 is sufficient to induce a metallic ground state. Evidence is found for a difference in the AFM structure of the Eu moments in the metallic crystals from that of undoped EuMn2As2 versus both T and H. For metallic Eu0.96K0.04Mn2As2 and Eu0.93K0.07Mn2As2, an anomalous S-shape T dependence of ρrelated to the Mn magnetism is found. Upon cooling from 200 K, ρexhibits a strong negative curvature, reaches maximum positive slope at the Mn TN ~ 150 K, and then continues to decrease but more slowly below TN. This suggests that dynamic short-range AFM order of the Mn spins above the Mn TN strongly suppresses the resistivity, contrary to the conventional decrease of ρthat is only observed upon cooling below TN of an antiferromagnet.