Conservation of angular momentum in the problem of tunneling of the magnetic moment

Tunneling of the magnetic moment has some unique features not encountered in other tunneling problems. The conservation of energy and angular momentum prohibits transitions between degenerate magnetic states in a free single-domain magnetic particle. For such transitions to occur, the particle must be firmly coupled with a large solid matrix that absorbs the change in the angular momentum. We show that the contribution of this effect to the tunneling rate is determined by the ratio of the magnetic anisotropy energy to the shear modulus of the matrix. An experiment is suggested that can test this prediction.