Powder neutron diffraction study of HoCoGa₅

We have studied successive magnetic transitions of HoCoGa₅ at T_N1 = 9.6 K and T _N2 = 7.5 K by using powder neutron diffraction. Apparent superlattice peaks were observed at temperatures below T_N1. With further decreases temperature, the patterns exhibit a substantial change at temperatures below T_N2. The observed magnetic peaks at 8 K (AntiFerromagnetic InCommensurate (AFIC) phase: T _N2 〈 T < T_N1) can be represented by the propagation vector q_L = (1/2 0 τ) with τ = 0.35(2). In contrast, the magnetic structure becomes commensurate with q_C = (1/2 0 1/2) at 4 K (AntiFerromagnetic Commensurate (AFC) phase: T < T_N2). The temperature dependence of magnetic intensity shows an apparent temperature hysteresis at T_N2, indicates a first-order transition at T_N2. Analysis of the integrated intensity at 4 K reveals that the Ho moment with a size of 8.6(2) μ_B, oriented parallel to the c-axis in the AFC phase. While the successive transitions of HoCoGa₅ are different from those of TbCoGa₅, the magnetic structure in the AFC phase of HoCoGa₅ is the same as the AF_I ^Tb of TbCoGa₅, and may indicate an additional transition at a lower temperature in HoCoGa₅.