A europium-151 Mössbauer spectral study of Eu₁₄MnP ₁₁, Eu₁₄MnAs₁₁, and Eu₁₄MnSb ₁₁

The europium-151 Mössbauer spectra of the Eu₁₄MnP ₁₁, Eu₁₄MnAs₁₁, and Eu₁₄MnSb ₁₁ Zintl compounds, measured between 4.2 and 100 K, reveal europium(II) for all four crystallographically inequivalent europium sites in Eu₁₄MnAs₁₁ and Eu₁₄MnSb₁₁ and europium(II) 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(II) magnetic moments are ordered, and hyperfine fields of 24.4, 24.8, and 19.3 T are observed in Eu₁₄MnP ₁₁, Eu₁₄MnAs₁₁, and Eu₁₄MnSb ₁₁, respectively, fields that are typical for magnetically ordered europium(II) ions. At 4.2 K the 16f europium(III) sites in Eu ₁₄MnP₁₁ experience a transferred hyperfine field of 33 T from the neighboring ordered europium(II) moments. Between its Curie temperature and 4.2 K, the europium-151 Mössbauer spectra of Eu₁₄MnSb ₁₁ reveal that the europium(II) 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 Mössbauer 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(III) hyperfine fields is preferred for its physical meaning and its reduced number of fitted parameters.