Interplay between localized and itinerant magnetism in Co-substituted FeGa 3

The evolution of the electronic structure and magnetic properties with Co substitution for Fe in the solid solution Fe1-xCoxGa3 was studied by means of ab initio band-structure calculations and nuclear spin-lattice relaxation 1/T1 of the 69,71Ga nuclei. The 69,71(1/T1) was studied as a function of temperature in a wide temperature range of 2-300 K for the concentrations x=0.0, 0.5, and 1.0. In the parent semiconducting compound FeGa3, the temperature dependence of the 69(1/T1) exhibits a huge maximum at about T∼6 K indicating the existence of in-gap states. The opposite binary compound, CoGa3, demonstrates a metallic Korringa behavior with 1/T1 T. In Fe0.5Co0.5Ga3, the relaxation is strongly enhanced due to spin fluctuations and follows 1/T1T1/2, which is a unique feature of weakly and nearly antiferromagnetic metals. This itinerant antiferromagnetic behavior contrasts with ab initio band-structure calculations, where a ferromagnetic state with an ordered moment of 0.5 μB/f.u. is predicted. The results are discussed in terms of the interplay between the localized and itinerant magnetism including in-gap states and spin fluctuations.