Physical properties of EuPd2As2 single crystals

The physical properties of self-flux grown EuPd2As2 single crystals have been investigated by magnetization M, magnetic susceptibility chi, specific heat Cp, and electrical resistivity rho measurements versus temperature T and magnetic field H. The crystal structure was determined by powder x-ray diffraction measurements, which confirmed the ThCr2Si2-type body-centered tetragonal structure (space group I4/mmm) reported previously. The rho(T) data indicate that state of EuPd2As2 is metallic. Long-range antiferromagnetic (AFM) ordering is apparent from the chi(T), Cp(T), and rho(T) measurements. For H \parallel c the chi(T) indicates two transitions at TN1 = 11.0 K and TN2 = 5.5 K, whereas for H \perp c only one transition is observed at TN1 = 11.0 K. Between TN1 and TN2 the anisotropic chi(T) data suggest a planar noncollinear AFM structure, whereas at T < TN2 the chi(T) and M(H,T) data suggest a spin reorientation transition in which equal numbers of spins cant in opposite directions out of the ab plane. We estimate the critical field at 2 K at which all Eu moments become aligned with the field to be about 22 T. The magnetic entropy at 25 K estimated from the Cp(T) measurements is about $11\%$ smaller than expected, possibly due to an inaccuracy in the lattice heat capacity contribution. An upturn in rho at T < TN1 suggests superzone energy gap formation below TN1. This behavior of rho(T < TN1) is not sensitive to applied magnetic fields up to H = 12 T.