We study tunneling of the magnetic moment in a particle that has full
rotational freedom. Exact energy levels are obtained and the ground-state
magnetic moment is computed for a symmetric rotor. The effect of the mechanical
freedom on spin tunneling manifests itself in a strong dependence of the
magnetic moment on the moments of inertia of the rotor. Energy of the particle
exhibits quantum phase transitions between states with different values of the
magnetic moment. Particles of various shapes are investigated and quantum phase
diagram is obtained.Comment: 7 Figures, 5 Figure Captions, submitted to PR
