Quantum-Spin-Liquid Corrections near a Transition to Strong Ferromagnetism*

The Curie temperature of bulk and nanostructured Fe₅Si₃ is investigated using experiments, density-functional simulations, and many-body model calculations. The bulk intermetallic, which crystallizes in the hexagonal D8₈ structure, exhibits several intriguing features: it does not exist as a room-temperature equilibrium phase, is close to the onset of ferromagnetism, and exhibits two crystallographically very different Fe sites. The samples, produced by rapid quenching (bulk) and cluster deposition (nanoparticulate thin films), have Curie temperatures of about 400 K, with a pronounced dependence on the Si content. Calculations using the Vienna ab-initio simulation package (VASP) show that the nanostructuring triggers a transition from weak to strong ferromagnetism. Interatomic exchange constants are calculated using the Kohn-Korringa-Rostoker (KKR) method and used to solve the multisublattice mean-field problem for the system, VASP calculations are used to study the dependence of the Fe moment on the thermally induced spin misalignment, and a model calculation yields an estimate for quantum-spin-liquid corrections.