Nonliner Effects Of Antiferromagnetic System In Vertical Magnetic Field

The resonant frequencies of typical antiferromagnetic(AF)materials are distributed over the far-infrared and millimeter ranges,they are also in THz ranges.Therefore,it is of practical interest to study the nonlinearity in the AF materials for the developing of THz technology.As a result of the weak AF nonlinearity,the method to enhance the AF nonlinearity is a very interesting issue.In this paper,the linear and nonlinear magnetization and susceptibility of the AF material in vertical magnetic field are calculated based on the Landau-Lifshitz equation as a foundation of the second harmonic generation(SHG)in this model,and the method to enhance SHG is discussed by the numerical simulation.The important results are given as follows:1.The derivations of nonlinear magnetization and magnetic susceptibility of the AF materials in vertical magnetic field are obtained.2.The method to enhance the SHG of antiferromagnetic film(AFF)in vertical magnetic field is discussed.While the frequency of incident electromagnetic wave is close to the resonant frequencies of AF,the intensity of SHG reach the maximum,and maximum is shown to increase with growth of the vertical magnetic field.The peak frequency of the SHG excited by TM waves shows red shift as the magnetic field increased,but the peak frequency of the SHG excited by TE waves show blue shift.The intensity of SHG is oscillated periodically as AF thickness increased,and the periodic length is about half of the equivalent wavelength of SHG.SHG output is also related to the incident angle and dielectric medium,it may be greatly enhanced by the total reflection of pump waves.It is feasible to enhance the intensity or regulate the properties of SHG output by changing the configuration of AF system,such as polarization mode,frequency,incident angle of electromagnetic wave,intensity of magnetic field,thickness of AFF and dielectric medium.