Frustrated magnetic behaviour of TbRh1.2Ru0.8Si2

TbRh1.2Ru0.8Si2 shows two magnetic ordering schemes coexisting at 1.5 K: a sine wave modulated antiferromagnetic structure described by the wave vecto r k= (0.445(1),0.015(1),0) and a collinear antiferromagnetic structure char acterized by the wave vector k = (1/2,1/2,1/2). The first phase is observed below the Neel point at 10 K, and the second coexists with the first below 5 K. In both structures the magnetic moments are localized on Tb3+ ions an d are aligned along the tetragonal axis. The magnetic structure of TbRhRuSi 2 has been confirmed to be a sine wave modulated antiferromagnetic structur e described by the wave vector k = (0.413(4),0,0) with magnetic moments par allel to the tetragonal axis. This structure is stable in the temperature r ange from 1.5 K to the Neel point at 15.5 K. (C) 2000 Elsevier Science S.A. All rights reserved.