Xuan-Zhang Wang and Shu-Fang Fu

Department of Physics

Harbin Normal University

Harbin 150080

P.R. China

Laboratory of Excited State Process

Chinese Academy of Science

Changchun 130021

P.R. China

We investigate nonlinear polaritons of
antiferromagnetic superlattices, or
antiferromagnetic multilayers. In the third-order
approximation, an effective-medium theory and a
coordinate system with the y axis normal the
interfaces, and sublattice magnetization and
anisotropy axis parallel to the z axis, are applied
to obtained the dispersion equations for the
polaritons in different geometries. These equations
show that the nonlinearity does not influence the
polaritons propagating in the x-y plane or along the
three axes, but influences clearly the polaritons
with wave vector in the x-z and y-z
planes. Numerical results tell us that the nonlinear
wavenumber shift versus frequency is always positive
for those polaritons in the bulk continuum above the
antiferromagnetic resonant frequency, but in the
continuum below this resonant frequency, the
nonlinear shift is negative in most of the frequency
region and is positive in a small region. Combine
linear dispersion curves, these results also show
that the relevant envelope solitons can exist in
most of the bulk continua, and cannot appear in the
small region mentioned above. The parameters for
numerical calculations come from the FeF_2\ZnF_2
superlattice.