Simulation And Theory Investigation Of Magnon Transmission In Magnetic Heterojunction

Spin waves or magnons,the eigenexcitations of the magnetically ordered media,are promising data carriers in next-generation information processing devices.The crucial advantages of magnonic devices are low energy,supporting transferring spin angle momentum,supporting manipulation by muti-physical field and so on.Thus,it enables the magnonic units to supplement or even replace charge-based complementary metal-oxide semiconductor(CMOS)circuits,realizing the higher performance computing chips.In this thesis,we mainly focus on investigating the magnon transmission in the magnetic heterojunction as follows:(1)The magnon transmission in sandwich structure of ferromagnetic insulator(FMI)/ antiferromagnetic insulator(AFI)/ ferromagnetic insulator(FMI)is investigated by atomistic spin model simulations.Magnon junction effect(MJE)which have been reported by experiments can be reproduced in our work,demonstrating the importance of spin dependent magnon blocking in this structure.Moreover,AFI spacers with various structures are investigated.We show that the MJE is sensitive to the characteristics of the AFI spacer such as orientation of Neel vector,types of AFI spin configuration and intrinsic exchange interaction.It is found that these phenomena are rooted in the magnon selection rules between two FMIs of different magnonic polarization.Based on the mechanism studied above,we further propose an in-plane MJE and give a feasible experimental prediction using nonlocal magnon-mediate current drag measurement.Our works provide insights into magnon transmission in MJ and will serve as a promising tool for future magnon circuits.(2)We theoretically study the scattering behavior of spin waves(SWs)at the interface of an antiferromagneticly coupled(AFMC)heterojunction.It is shown that the SWs passing through the interface are evanescent and the incident waves are all reflected back,demonstrating a magnetization-dependent magnon blocking effect in this structure.We also analytically derive the expressions for the decay length of the evanescent waves(EWs).The theoretical result indicates that with the increase of the spin-wave frequency,the decay length decreases and the EWs are more concentrated at the interface,showing a magnonic skin effect which is similar to the skin effect of electromagnetic waves.Furthermore,a positive magnonic Goos-H?nchen shift of the reflected waves is also predicted.It can be understood by an effective reflection interface shift induced by the non-zero decay length of the EWs.The results of micromagnetic simulations are consistent well with all the theoretical findings.Based on the above findings,we also propose a magnon valve without spacers,which shows100% on-off ratio for magnons.Our work provides insights into SW transmissions in the system of AFMC heterostructures and will serve as a promising tool for future magnonic devices.(3)The inverse design(ID)approach is developed for designing the magnonic filters(MFs).To determine the optimizable variables,the fundamental properties of antiferromagneticlly coupled heterojunction based magnonic crystals were theoretically investigated.The particle swarm algorithms(PSA)are used for automatically finding magnonic filters(MFs)which meet the inputting requirements.Here,the input of algorithms is a vector of SW frequency and output is a vector of parameters of MFs.Besides,the PSA is further optimized to be self-adapting to required accuracies,showing a higher computing efficiency than the convectional one.Finally,the output data of predicted MFs with various filtering characteristics are briefly summarized in a table as an alternative proposal for the future experimental design.These encouraging results show high potential of using ID approach in magnetism and boosting optimization of magnetic multilayer heterojunction devices.