Macroscopic quantum effect in single domain antiferromagnetic particles in an external magnetic field

The effect of the external magnetic field on macroscopic quantum tunneling in biaxial single domain antiferromagnetic particles is studied with the help of the instanton method. It is shown that the decay rate increases with increasing external magnetic field applied along the easy axis of the magnetization, and that the tunneling splitting oscilates with respect to the external magnetic field in the direction of the medium axis. Our results may be helpful for experimental observation of the macroscopic quantum coherence and the tunneling decay in single domain antiferromagnetic particles.