Nanospheres of a new intermetallic FeSn₅ phase: Synthesis, magnetic properties and anode performance in li-ion batteries

We synthesized monodisperse nanospheres of an intermetallic FeSn ₅ phase via a nanocrystal-conversion protocol using preformed Sn nanospheres as templates. This tetragonal phase in P4/mcc space group, along with the defect structure Fe_0.74Sn₅ of our nanospheres, has been resolved by synchrotron X-ray diffraction and Rietveld refinement. Importantly, FeSn₅, which is not yet established in the Fe - Sn phase diagram, exhibits a quasi-one dimensional crystal structure along the c-axis, thus leading to interesting anisotropic thermal expansion and magnetic properties. Magnetization measurements indicate that nanospheres are superparamagnetic above the blocking temperature T_B = 300 K, which is associated with the higher magnetocrystalline anisotropy constant K = 3.33 kJ m^{- 3}. The combination of the magnetization measurements and first-principles density functional theory calculations reveals the canted antiferromagnetic nature with significant spin fluctuation in lattice a - b plane. The low Fe concentration also leads Fe_0.74Sn₅ to enhanced capacity as an anode in Li ion batteries.