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

Abstract

Powder neutron diffraction analysis was performed on Tm 11 B 4 , which undergoes successive transitions at T N 1 =11.7 K, T * =11 K, and T N 2 =10 K. An incommensurate structure with two propagation vectors, k 2 =[1± k '± k '', ± k '', 0] and k 2 '=[1± k '±3 k '', ± k '', 0] ( k '=0.1226 and k ''≃0.012), is suggested for phase II ( T * ≤ T ≤ T N 1 ). Phase III ( T N 2 ≤ T ≤ T * ) is described by one propagation vector, k 3 =[1± k ',0,0]. The propagation vector for phase IV ( T ≤ T N 2 ) further changes to a commensurate one characterized by k 4 =[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 N 2 up to 20 K.