Quantum dynamics of crystals of molecular nanomagnets inside a resonant   cavity
  It is shown that crystals of molecular nanomagnets exhibit enhanced magnetic relaxation when placed inside a resonant cavity. Strong dependence of the magnetization curve on the geometry of the cavity has been observed, providing evidence of the coherent microwave radiation by the crystals. A similar dependence has been found for a crystal placed between Fabry-Perot superconducting mirrors. These observations open the possibility of building a nanomagnetic microwave laser pumped by the magnetic field. 
J. Tejada, E. M. Chudnovsky, R. Amigo, and J. M. Hernandez