Giant Negative\nMagnetization in Al_9–<i>x</i>Fe_<i>x</i>Mo₃

Abstract

We present derivatives of the Al₃Ti-type of\nstructure\nAl₈FeMo₃ (Al_9–<i>x</i>Fe_<i>x</i>Mo₃) and Al₈CuMo₃. Structural features are a molybdenum-square lattice\nand a solid solution of iron (copper) on aluminum sites. By substitution\nof Al with 3d-transition metals outstanding magnetic properties are\nfound. Typical Pauli paramagnetism is observed above a critical temperature <i>T</i>_c ≈ 93 K. Below <i>T</i>_c the series Al_9–<i>x</i>Fe_<i>x</i>Mo₃ (0.5 < <i>x</i>_Fe < 1) exhibits the rare coexistence of negative magnetization/diamagnetism\nin zero-field cooling and ferromagnetism in field-cooling mode. For\nAl_8.33Fe_0.67Mo₃ the negative magnetization\nis estimated to the order of ∼50% of the diamagnetic response\nof superconducting lead. The contribution of Fe to the magnetization\nis evaluated by ⁵⁷Fe Mössbauer spectroscopy in zero\nfield and applied external fields. We show that ferromagnetic fluctuations\noriginate from screened magnetic moments of Fe. The magnetic order\npresumably involves multibands originating from iron and molybdenum\nin the vicinity of the Fermi energy. Further insights into anomalous\nelectron–phonon coupling are gained.