Terahertz Magnetic Response Of Magnetic Nanostructures

At present,with the rapid development of electronic information technology,the occupation rate of microwave frequency band is getting higher and higher,which has a great impact on the transmission speed and quality of signals.The terahertz frequency band is a frequency band that has not yet been fully developed.Terahertz waves have higher frequencies,stronger penetration,and narrower beams,which have great potential for applications in medical imaging and precise positioning.However,conventional materials cannot exhibit a strong magnetic response in this frequency band,which has led to stagnation of terahertz technology for a long time.It was not until the emergence of artificial metamaterials with obvious magnetic response in the terahertz frequency band that terahertz technology was reborn.It is worth noting that the commonly used terahertz metamaterials are materials with periodic structures designed with electromagnetic software.The fabrication of metamaterials require micro-size processing and the cost is high,which is a very big challenge for large-scale commercial applications.In this thesis,a remarkable magnetic response in the terahertz frequency band was obtained by micromagnetic simulation using L10-FePt nanowires,L10-FePt nanowire arrays and SmCo5 thin films,which are natural permanent magnet materials with extremely high magnetocrystalline anisotropy.Firstly,as for the simulation of L10-FePt nanowires,it is found that the magnetic response of the nanowires in the spontaneous magnetization state is mainly concentrated in the microwave frequency band,and cannot show a high magnetic response in the terahertz frequency band.However just adjusting its magnetization state,when its remanence ratio(Mr/Ms)is 1,a unique and significant magnetic response occurs at 0.348 THz.And in the simulation results of L10-FePt nanowires,the imaginary part phenomenon of negative permeability,which is different from that of conventional magnetic materials,appears.By comparing the magnetic moment precession of L10-FePt nanowires and Fe nanowires,it is believed that the reason for this phenomenon is that the anomalous precession of magnetic moment of L10-FePt nanowires produces a negative equivalent damping factor.And it is further verified from the results of energy loss.Secondly,this thesis showed a certain regulation of the terahertz magnetic response of L10-FePt nanowires by changing the size,grain size and grain orientation of L10-FePt nanowires.Based on the research results of a single L10-FePt nanowire,the terahertz magnetic response of the L10-FePt nanowire array was explored,and it was found that due to the negative effect of the interaction energy between the nanowires,the frequency of the terahertz magnetic response of the nanowire array was generally lower than that of a single L10-FePt nanowire array.And the larger the nanowire spacing,the smaller this side effect,and the larger the terahertz magnetic response frequency of the nanowire array.Finally,in the last chapter of thesis,the remanent magnetization state of the SmCo5 film was used to obtain a significant terahertz magnetic response near 1 THz,and the effects of remanent state along different directions(in the plane of film and perpendicular to the film plane)and the thickness of film on the terahertz magnetic response of the SmCo5 film were also investigated.