151Eu Mössbauer spectroscopic, electric, and magnetic measurements of EuAgGe and EuAuGe

The physical properties of EuAgGe and EuAuGe, the structures of which are derived from the CeCu₂ type, have been investigated in detail by means of magnetic susceptibility, electrical conductivity and ¹⁵¹Eu Mössbauer measurements. Above 50 K both germanides show Curie--Weiss behavior with experimental magnetic moments of \mu _exp=7.70(5) \mu _B (EuAgGe) and \mu _exp=7.40(5) \mu _B (EuAuGe) and Weiss constants of -2(1) K (EuAgGe) and 33(1) K (EuAuGe). For EuAgGe, a magnetic phase transition is observed below 18(1) K. Zero-field cooling and field cooling measurements indicate cluster glass behavior (weak ferromagnetism, mictomagnetism). Magnetization measurements at 5 K show a saturation magnetic moment of 3.3(2) \mu _B/Eu at 5.5 T. ¹⁵¹Eu Mössbauer measurements show a Eu(II) valence state (\delta =-10.4 mm/s). While magnetic hyperfine splitting appears in the spectra at temperatures as high as 15 K, complete magnetic ordering is not reached at temperatures down to 4.2 K. EuAuGe orders ferromagnetically at 32.9(2) K. Magnetization measurements at 2 K show a saturation magnetic moment of 6.2(1) \mu _B/Eu at 5.5 T, respectively, indicating that all spins are ordered ferromagnetically at low temperatures. ¹⁵¹Eu Mössbauer measurements show a Eu(II) valence state (\delta =-10.6 mm/s) and two spectral components in an approximate 1:1 ratio, subjected to magnetic hyperfine splitting effects at T₁=32(2) and T₂=18(4) K, respectively. Thus, the transition temperature of 32.9 K observed in the susceptibility measurements appears to be associated with ordering of only one of the two crystallographically distinct europium sites in this compound. Electrical conductivity measurements indicate metallic behavior for both germanides.