The tilted helix: an intermediate magnetic phase

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Abstract
In a system of localized spins interacting via an exchange favouring helical ordering there is a region of 'forbidden' axial anisotropy separating normal flat and conical spirals as the stable orders. The stable phase in the intermediate region is shown to be a tilted helix corresponding to tilting the planes of a normal flat spiral together with additional perturbations of pitch and out-of-plane wobble. An investigation is presented of the ordering, stability and excitation of this intermediate phase. It is proposed that the model provides an explanation of intermediate phases seen in Er-Tb, Er-Dy alloys and also Er metal itself. It is suggested that similar intermediate phases may exist in Ho and certain other alloys, although unconsidered magnetostrictive or other forces could lead to discontinuities which prevent their manifestation.