Squeezed States of Damon–Eshbach-Like Modes in Ferromagnetic Films Under Microwave Pumping

A theoretical account is given for the non-classical properties of magnons in ultra-thin ferromagnetic films with in-plane magnetization under the conditions of parallel pumping. A microscopic or Hamiltonian-based approach with a lattice of effective spins interacting through the magnetic dipole-dipole and exchange interactions is used. With the Zeeman energies of the static applied field and the microwave pumping field included, the total Hamiltonian is transformed from spin operators to boson creation and annihilation operators. Using a representation of coherent magnon states, we obtain the explicit results for the temporal evolution of the magnon occupation number as well as the magnon squeezing. In particular, it is shown that the manipulation of the collapse-and-revival phenomena for the average number of magnons and the properties of the magnon squeezing is made possible by controlling the nonlinearity in the system through the microwave pumping field.