A europium-151 Mossbauer spectral study of Eu14MnP11, EuMnAs11, and Eu14MnSb11

The europium-151 Mossbauer spectra of the EU14MnP11, Eu14MnAs11, and Eu14MnSb11 Zintl compounds, measured between 4.2 and 100 K, reveal europium(11) for all four crystallographically inequivalent europium sites in EU14MnAs11 and Eu14MnSb11 and europium(11) and europium(III) for the three 32g and the 16f europium sites in Eu14MnP11, respectively. Below the ordering temperatures of 52, 74, and 92 K, only very small hyperfine fields of 2-4 T are observed at the europium sites as a result of the polarization by the manganese magnetic moments. At 4.2 K, the europium(11) magnetic moments are ordered, and hyperfine fields of 24.4, 24.8, and 19.3 T are observed in Eu14MnP11, Eu14MnAs11, and Eu14MnSb11, respectively, fields that are typical for magnetically ordered europium(11) ions. At 4.2 K the 16f europium(III) sites in EU14MnP11 experience a transferred hyperfine field of 33 T from the neighboring ordered europium(11) moments. Between its Curie temperature and 4.2 K, the europium-151 Mossbauer spectra of Eu14MnSb11 reveal that the europium(11) moments order below ca. 13 K, i.e., below the second magnetic transition observed in magnetic measurements. Between their Curie temperatures and 4.2 K, the europium-151 Mossbauer spectra of EU14MnP11 and EU14MnAs11 are complex and have been analyzed with two models, models that give equivalently good fits. However, the second model in which the spectra are fit with a three-dimensional relaxation of the europium(II) and europium(Ill) hyperfine fields is preferred for its physical meaning and its reduced number of fitted parameters.