Structural phase transition in Al-substituted Fe_2MnCa Heusler alloy

摘要

In this work, we have systematically investigated the face centered cubic (FCC) to body centered cubic (BCC) transition and its influence on hyperfine and magnetic properties of Al-substituted Fe2MnGa laminated metallic ribbons (non-annealed and annealed) prepared by arc-melting. X-ray diffraction results of non-annealed ribbons show the formation of the atomically disordered FCC (A1) phase in low Al-content (30 at. %), while a full atomically disordered BCC phase (A2) is found for high Al-content (= 50 at. %). An ordered cubic phase (L2(1)-structure) is established in plastically deformed Al-substituted alloys annealed at 573 K for a few hours. In the L2(1) state, the Al content increase induces a linear reduction of the cubic cell volume, which influence s and d-electron charge and spin densities at Fe atoms. These changes are responsible for the modifications in hyperfine and magnetic properties of the studied alloys, as confirmed by first principles calculation. We have also demonstrated that the L2(1) state can be obtained when small percentages (5 at.%) of Al replace Ga atoms and the structural transition is basically explained by an enhancement of chemical pressure in the Al isoelectronically substituted Fe2MnGa system. Published under license by AIP Publishing.