Single-spin irreducible spherical tensor operators T(k,m). The resulting spherical tensors are normalized in such a way as to obey the following commutation relation:
mult - multiplicity of the spin in question k - irreducible spherical tensor rank (optional)
T - a two-argument call returns a cell array of tensors of rank k in the order of decreasing projection. A single argument call produces tensors of all ranks and puts them into a cell array in the order of increasing rank.
Operator normalization in spin dynamics is a thorny question. The only way to make the resulting formalism independent of the total spin quantum number is to impose identical commutation relations rather than equal matrix norms.