NMR and Mössbauer study of spin-glass behavior in FeAl₂

We have used NMR and Mössbauer spectroscopy to investigate the magnetism and spin-glass behavior in FeAl₂. The results show that the observed behavior can be interpreted as local-moment magnetism residing on the Fe sites. An increase in ⁵⁷Fe Mössbauer magnetic hyperfine field was observed at the 35-K spin-glass freezing temperature, with a reduced low-temperature value consistent with unquenched fluctuations in the spin-glass state. However, the ²⁷Al NMR shifts and spin-lattice relaxation behavior are consistent with transfer hyperfine interactions to Fe local moments, with a magnitude of approximately 2.5 μ_B. This value is consistent with the bulk magnetization, but surprising compared to other Fe aluminides, given the small Fe-Fe coordination number and associated weakening expected for the magnetic moment.