= Bipartite spin rotation
A <bipartite spin rotation> rotates the <spin> on one sublattice by $\pi$, converting an alternating classical <Néel state> to an all-up reference state. Rotation about $x$ sends $S^z\mapsto-S^z$ and $S^\pm\mapsto S^\mp$ on that sublattice. For an isotropic nearest-neighbor <Heisenberg antiferromagnet>, a bond becomes $-S_i^zS_j^z+(S_i^+S_j^++S_i^-S_j^-)/2$. The transformation is unitary and preserves the <spin commutation relations>; it changes the reference frame, not the model's spectrum.
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