Type-I antiferromagnetic structure

The anisotropy of the RKKY interaction usually leads to rather complex magnetie struetures. In particular, nesting of the Fermi surface can have dramatic effects. An exemplary system is CeAlj (Steglieh et al. 1979b) its spin arrangement displays a type-II antiferromagnetic structure in which the magnetic moments are parallel to [111] and point into opposite directions on the lattice sites (0,0,0) and (3,5,5). The moments are modulated by an ineommensurate wavevector (i + t, 5 — t, 5) with t = 0.11 (Barbara et al. 1977). 

Fig. 7.16. (a) Possible magnetic structure of HoN [after Child et al. (1963)]. (b) Mn-0 type (Type II) antiferromagnetic structure. The open circles represent the magnetic atoms with + and - symbols denoting moments parallel and antiparallel to the [111] direction. The closed circles represent the non-magnetic atoms, (c) Magnetic structure of HoP [after Child et al. (I%3)]. 

With a few exceptions, the crystal structure of the salts based on the type I mixed chains consists of parallel arrangements of those chains. In most cases the magnetic behavior of these salts is dominated by ferromagnetic (FM) interactions, due to intrachain D+ A coupling. Several of these salts exhibit metamagnetic (MM) behaviors due to the coexistence of weaker antiferromagnetic (AF) intrachain interactions. 

UAs-US Lam and Aldred (1974) summarized the magnetization and neutron diffraction experiments. The Neel temperatures decrease with increasing US concentration, whereas the transition temperature from type I to lA antiferromagnetism increases. At 20% US only the lA structure is stable. Thereafter the moments are no longer commensurate with the lattice in the vicinity of the Neel temperature. For more than 40% US the samples are ferromagnets. 

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