Single crystals of EuCu2As2 and EuCu2Sb2 were grown from CuAs and CuSb
self-flux, respectively. The crystallographic, magnetic, thermal and electronic
transport properties of the single crystals were investigated by
room-temperature x-ray diffraction (XRD), magnetic susceptibility \chi versus
temperature T, isothermal magnetization M versus magnetic field H, specific
heat Cp(T) and electrical resistivity \rho(T) measurements. EuCu2As2
crystallizes in the body-centered tetragonal ThCr2Si2-type structure (space
group I4/mmm), whereas EuCu2Sb2 crystallizes in the related primitive
tetragonal CaBe2Ge2-type structure (space group P4/nmm). The energy-dispersive
x-ray spectroscopy and XRD data for the EuCu2Sb2 crystals showed the presence
of vacancies on the Cu sites, yielding the actual composition EuCu1.82Sb2. The
\rho(T) and Cp(T) data reveal metallic character for both EuCu2As2 and
EuCu1.82Sb2. Antiferromagnetic (AFM) ordering is indicated from the \chi(T),
Cp(T), and \rho(T) data for both EuCu2As2 (T_N = 17.5 K) and EuCu1.82Sb2 (T_N =
5.1 K). In EuCu1.82Sb2, the ordered-state \chi(T) and M(H) data suggest either
a collinear A-type AFM ordering of Eu+2 spins S=7/2 or a planar noncollinear
AFM structure, with the ordered moments oriented in the tetragonal ab plane in
either case. This ordered-moment orientation for the A-type AFM is consistent
with calculations with magnetic dipole interactions. The anisotropic \chi(T)
and isothermal M(H) data for EuCu2As2, also containing Eu+2 spins S=7/2,
strongly deviate from the predictions of molecular field theory for collinear
AFM ordering and the AFM structure appears to be both noncollinear and
noncoplanar.Comment: 21 pages, 22 figures, 4 Table
