QUANTUM DECAY OF METASTABLE STATES IN SMALL MAGNETIC PARTICLES

We present an imaginary-time path-integral study of the problem of qua ntum decay of a metastable state of a uniaxial magnetic particle place d in the magnetic field at an arbitrary angle. Our findings agree with earlier results of Zaslavskii obtained by mapping the spiral Hamilton ian onto a particle Hamiltonian. In the limit of low barrier, weak dep endence of the decay rate on the angle is found, except for the field which is almost normal to the anisotropy axis, where the late is sharp ly peaked, and for the field approaching the parallel orientation, whe re the rate rapidly goes to zero. This distinct angular dependence, to gether with the dependence of the rate on the field strength, provides an independent test for macroscopic spin tunneling.