MQT in a free NP

Quantum tunneling of the magnetic moment in a free nanoparticle.
M.F. O'Keeffe, E.M. Chudnovsky, D.A. GaraninJMMM 324, 2871 (2012)

Dependence of energy on J at K=J   and _Iz/_Ix=2$I_z/I_x=2$ for different values of α$\alpha$. The plot shows first-order quantum phase transition on α$\alpha$.