The spin is classically declared by comparison with a rotary motion of particles. But this is impossible like Bohr's assumption, the electrons circulate around the atomic nucleus.
It should be better to declare "spin" as asymmetry of the electrical charge or a directed electrical field. In close range the asymmetry is very effective and also observable, in far range this asymmetrie lose its effectiveness and electrons/positrons have apparently a spherical charge.
Spin-spin-interactions between electrons, electrons/positrons and positrons would be better explainable and much more besides.