57Fe Mössbauer spectroscopy and magnetic study of Al13Fe4

Abstract

The results of ab initio electronic structure and electric field gradient (EFG) calculations, and of X-ray diffraction, 57Fe Mössbauer spectroscopy, and magnetic studies of Al13Fe4 are reported. It is shown that Al13Fe4 crystallizes in the monoclinic space group C2/m, in which Fe atoms are located at five inequivalent crystallographic sites, with the lattice parameters a=15.503(2)Å, b=8.063(2)Å, c=12.464(2)Å, and β=107.71(2)°. We demonstrate that zero-field Mössbauer spectra can be decomposed into three quadrupole doublets. With the aid of the calculated EFG parameters we show that the first doublet results from one Fe site, the second doublet is due to two other Fe sites, and the third doublet originates from the last two Fe sites. We find that the shape of the Mössbauer spectrum of Al13Fe4 measured in an external magnetic field of 90kOe can be accounted for with five component subspectra generated using the calculated EFG parameters at five inequivalent Fe sites. The quadrupole splittings corresponding to three component doublets are shown to increase with decreasing temperature and are well described by a T3/2 power-law relation. The Debye temperature of Al13Fe4 is found to be 383(3)K. We find a pseudogap in the density of states (DOS), with a width of ∼0.2eV, that is centered 0.1eV above the Fermi energy. The finite DOS at the Fermi energy confirms good metallicity of Al13Fe4. The 1/T-like dependence of the magnetic susceptibility shows that Al13Fe4 is a paramagnet.