Giant Negative Magnetization in Al_9–xFe_xMo₃

We present derivatives of the Al3Ti-type of structure Al8FeMo3 (Al9–xFexMo3) and Al8CuMo3. Structural features are a molybdenum-square lattice and a solid solution of iron (copper) on aluminum sites. By substitution of Al with 3d-transition metals outstanding magnetic properties are found. Typical Pauli paramagnetism is observed above a critical temperature Tc ≈ 93 K. Below Tc the series Al9–xFexMo3 (0.5 < xFe < 1) exhibits the rare coexistence of negative magnetization/diamagnetism in zero-field cooling and ferromagnetism in field-cooling mode. For Al8.33Fe0.67Mo3 the negative magnetization is estimated to the order of ∼50% of the diamagnetic response of superconducting lead. The contribution of Fe to the magnetization is evaluated by 57Fe Mössbauer spectroscopy in zero field and applied external fields. We show that ferromagnetic fluctuations originate from screened magnetic moments of Fe. The magnetic order presumably involves multibands originating from iron and molybdenum in the vicinity of the Fermi energy. Further insights into anomalous electron–phonon coupling are gained.