Cobalt content- and magnetic field-dependent transmission behaviors of red laser light for CoAl2O3 granular thin films

The transmission of red laser light with wavelength λ = 632.8 nm of Cox-(Al2O3)1-x magnetic granular thin films was investigated under the effect of external magnetic field H (0-500 Oe). Results showed the behaviors of variation in the T transmittance ratio as a function of H exhibit three trends depending on the Co content x: (1) T declines to a saturation value called the floor level of the transmission Tflo when x < 0.49; (2) T tends to reach a maximum and then decreases to a saturation floor level when x = 0.49; and (3) T increases to a saturation value called the ceiling level of the transmission Tcei, when x > 0.49. Tflo increases in accordance with x when x < 0.49, whereas Tcei decreases rapidly when x approaches 1. These phenomena were considered to be related to the magnon-plasmon interactions from excitation by photons for the spins polarized in the Co particles.