Mössbauer study of the ferroelectric state in Ga-substituted CuFeO₂

₅₇Fe Mössbauer spectroscopic measurements have been conducted on CuFe_1-xGa_xO₂ single crystals, in order to investigate the magnetic structures and hyperfine parameters in ferroelectric CuFe_0.965Ga_0.035O₂ and paraelectric CuFeO₂. We confirmed that the Mössbauer spectrum at 4.2K in CuFeO₂ is explained by the collinear antiferromagnetic structure with spins along the hexagonal c-axis. In the ferroelectric phase in CuFe_0.965Ga_0.035O₂, the spectrum consists of three magnetic components, where magnetic hyperfine fields distribute in three different directions within the (110) plane. This configuration is not completely consistent with a simple proper screw structure with a uniform spin distribution. The quadrupole coupling constants e²qQ/2 are unexpectedly large for both specimens. In the ferroelectric state in CuFe _0.965Ga_0.035O₂, e²qQ/2 becomes noticeably smaller than that in the paraelectric phase in CuFeO₂. We discuss the difference in quadrupole coupling constant between the ferroelectric and paraelectric states in CuFe_1-xGa_xO₂.