Magnetic hyperfine field splitting in EuAg4As2 and EuAg4Sb2

The CaCu4P2-type pnictides EuAg4As2 and EuAg4Sb2 both contain stable divalent europium. Temperature dependent magnetic susceptibility measurements revealed experimental magnetic moments of 7.91(1) and 8.00(1) μB/Eu atom for the arsenide and antimonide, respectively. This is supported by 151Eu Mössbauer spectra which show isomer shifts of −11.33(1) (EuAg4As2) and −11.71(1) mm/s (EuAg4Sb2). Both pnictides show antiferromagnetic ordering below Néel temperatures of 14.9(5) (EuAg4As2) and 11.0(5) K (EuAg4Sb2). The antiferromagnetic ground state is only stable at low field strength. Metamagnetic transitions occur at critical field strengths of 4.4 (arsenide) and 2.4 kOe (antimonide) with saturation near 7 μB at 80 kOe and 5 K, indicating full parallel spin alignment. This is expressed by large magnetic hyperfine fields of 27.6(1) and 26.2(1) T at the europium nuclei of EuAg4As2 and EuAg4Sb2, respectively. 121Sb data of EuAg4Sb2 show a transferred hyperfine field of 9.8(2) T.