Magnetism in Fe$_{4}$Al$_{13}$ and related FeAl intermetallics

We report the results of an experimental study of FeAl alloys, including Fe$_{4}$Al$_{13}$, FeAl$_{2}$ and Fe$_{2}$Al$_{5}$. By using NMR, dc magnetic susceptibility, and specific heat, we found that Fe$_{4}$Al$_{13}$ and Fe$_{2}$Al$_{5}$ are non-magnetic with some dilute magnetic moments, while FeAl$_{2}$ can be characterized as a concentrated local moment system. Fe$_{4}$Al$_{13}$ is a decagonal quasicrystal approximant with 102 atoms in its unit cell. The $^{27}$Al NMR spin-lattice relaxation indicates a very narrow pseudogap in the electronic density of states [$g(E)$] in the vicinity of the Fermi energy. The observations could be fit assuming a parabolic variation of $g(E)$, consistent with observations in other quasicrystals and approximants. NMR lineshape measurements also agree with this analysis, and show that the system is dilute-magnetic, in strong contrast to the FeAl$_{2}$ ordered intermetallic. We use specific heat to analyze the dilute moment density. This work was supported by the Robert A. Welch Foundation, Grant No. A-1526, by the National Science Foundation (DMR-0103455), and by Texas A\&M University through the Telecommunications and Informatics Task Force.