  An explicit form of the magnetic moment tensor operator for non-Dirac
particles with rest spin 1/2 and its essential difference from the spin
operator are established. Possible consequences of the last fact for the
description of the spin rotation in the magnetic field and for the values of
magnetic moments of some nuclei, as well as the impact of this and other facts
on the validity of modelling the azimuthal asymmetry of the secondary-scattered
protons in $ep$-experiments are noted.
