Temperature Evolution of the Double Umbrella Magnetic Structure in Terbium Iron Garnet

The rare earth iron garnets RE3Fe5O12 (REIG hereafter) have been discovered at Grenoble (France) (Bertaut & Forrat, 1956; Bertaut et al., 1956) then independently at Murray Hill (USA) (Geller & Gilleo, 1957a, 1957b). These most studied ferrimagnetic materials have a general formula {RE3+3}[Fe3+2](Fe3+3)O12 where RE3+ can be any trivalent rare earth ion or the Yttrium Y3+. The crystal structure is described by the cubic space group Ia 3 d-( 10 Oh ) No. 230. Three type of brackets are used to indicate the different coordinations of the cations with respect to the oxygen O2– ions situated in the general positions x, y, z of the sites 96h(1) (Fig. 1). The RE3+ ions are located in the dodecahedral sites {24c}(222) whereas the two Fe3+ ions are distributed in the octahedral [16a]( 3 ) and tetrahedral (24d)( 4 ) sites.