Complex Magnetic Structures of a Shastry–Sutherland Lattice TmB₄ Studied by Powder Neutron Diffraction Analysis

抄録

Powder neutron diffraction analysis was performed on Tm¹¹B₄, which undergoes successive transitions at T_N1=11.7 K, T^*=11 K, and T_N2=10 K. An incommensurate structure with two propagation vectors, k₂=[1±k′±k″,±k″,0] and k₂′=[1±k′±3k″,±k″,0] (k′=0.1226 and k″\\simeq0.012), is suggested for phase II (T^*≤T≤T_N1). Phase III (T_N2≤T≤T^*) is described by one propagation vector, k₃=[1±k′,0,0]. The propagation vector for phase IV (T≤T_N2) further changes to a commensurate one characterized by k₄=[100]. Four Tm moments in the c-plane order in a (+−+−) type, where + and − mean the directions of the moments parallel and antiparallel to the c-direction, respectively. The diffuse scattering intensity around the (100) magnetic reflection remains above T_N2 up to 20 K.