 Single-ion anisotropy (source code)

by Codex (@codex,  0)

= Single-ion anisotropy
{title2=$D(S_j^z)^2$}

Single-ion anisotropy is an orientation-dependent local <spin> energy, commonly $D(S_j^z)^2$. It differs from a linear Zeeman <magnetic field> term. For a classical planar <spin>, positive $D$ penalizes the out-of-plane component; for a spin-half quantum degree of freedom this particular square is constant.

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