Electronic Structure and Magnetovolume Instabilities of the Hexagonal Laves Phase Compound Fe2Ti

We investigate the electronic and cohesive properties of the hexagonal and cubic Laves phases of Fe2Ti by ab initio band structure calculations. In particular the stability range of these compounds is studied. In the volume range considered, the state of lowest energy is hexagonal (C14) and exhibits antiferromagnetic order. However, we find a slightly higher in energy lying ferromagnetic state with low magnetic moment (smaller than l pB) . Interestingly enough, this moment can considerably be enhanced (larger than 1.5 pB) for larger lattice spacings. The characteristic moment-volume dependence of the Fe atom can also account for the experimental observation that Fe2+,Til-, is ferromagnetic for x>O since the smaller Fe atom leads to a contraction of the lattice which stabilizes large ferromagnetic iron clusters.