Basal plane anisotropy magnetoelastic

The assumption of a perfectly regular spiral (or cone) in the previous section led to the vanishing of the hexagonal basal plane and magnetoelastic anisotropies from the expression for the energy. The effect of these smaller terms will be to... 

Expansion of the function Bj in a Fourier series in q R-,) and applications of the Bloch theorem to the sum over i in eq. (7.24) leads to peaks in x whenever qm is a sub-multiple of a c-axis reciprocal lattice vector. The same argument can be made in the case of a spiral structure. The reasons for the incommensurate-to-commensurate q transition are to be found in (a) the single-ion anisotropy terms in the hamiltonian, including magnetoelastic effects. For CAM-type structures the axial anisotropy favors maximum ordered moment at each site which can only develop in a commensurate structure. For spiral-type structures the basal plane anisotropy will also favor a commensurate structure, as will the nagnetoelastic anisotropy (b) the exchange will also favor a maximum ordered... 

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