Crystal structure and magnetic properties of intermetallic semiconductor FeGa₃ lightly doped by Co and Ni

We have explored the crystal structure and magnetic properties of two intermetallic solid solutions of the IrIn₃ structure type. Although Fe_0.95Co_0.05Ga₃ and Fe_0.975Ni_0.025Ga₃ are isomorphous and possess exactly the same concentration of valence electrons, they display noticeable differences in their crystal structure associated with a different nature of the Fe–Co and Fe–Ni dumbbells. The former contains an odd number of electrons compared to an even number of the latter dumbbell. Responding to localized spins of the Fe–Co dumbbells, the ⁶⁹Ga NQR relaxation rate in Fe_0.95Co_0.05Ga₃ is governed by temperature independent spin-lattice relaxation typical for diluted paramagnetic centers at low temperatures. In Fe_0.975Ni_0.025Ga₃ with zero magnetic moment of the dumbbells the ⁶⁹Ga spin-lattice relaxation rate is strongly reduced and in-gap states in the energy gap show up as a broad maximum near 70 K.