27Al NMR insight into the phase transition in BaFe2Al9

We have applied 27Al nuclear magnetic resonance (NMR) spectroscopy to investigate the iron-based aluminide of BaFe2Al9. This material has been a subject of current interest due to indications of charge density wave behavior below the transition temperature TC <^> 100 K. Two sets of the 27Al NMR resonance lines that are associated with two nonequivalent crystallographic aluminum sites have been well resolved. We have discussed the obtained electric field gradient and anisotropic Knight shift for each individual aluminum site, revealing the strong ab plane bonding configuration for the structural properties of BaFe2Al9. Pronounced features in the isotropic Knight shift and nuclear spin-lattice relaxation rate have been observed in the vicinity of TC. Furthermore, the detailed 27Al NMR analyses have provided evidence for the decrease of the electronic density of states upon lowering temperature below TC.