Non-collinear antiferromagnetic structure in TbCoGa

Tokunaga, Yo  ; Saito, Yo*; Sakai, Hironori   ; Kambe, Shinsaku  ; Sanada, Naoyuki*; Watanuki, Ryuta*; Suzuki, Kazuya*; Kawasaki, Yu*; Kishimoto, Yutaka*

We report NMR studies of TbCoGa, which has the tetragonal HoCoGa structure and exhibits two antiferromagnetic (AF) transitions at =36.2 K and =5.4 K. From analysis of the internal fields at Ga sites, we have determined the magnetic structures of the AF-I () and the AF-II () phases. The AF-I phase is a collinear AF order with the propagation vector q=[1/2, 0, 1/2] and with ordered moments parallel to the c axis. This is in accordance with the neutron diffraction measurements. In the AF-II phase, on the other hand, we found a non-collinear AF structure described with double propagation vectors =[1/2, 0, 1/2] and =[0, 1/2, 1/2]. Interestingly, the NMR reveals that the c component of the Tb moments does not change value between the AF-I and the AF-II phases, even though an a component is newly developed in the AF-II phase.