| Cavity spintronics is a new field to study the coupling between the cavity photons and the magnon.Its main purpose is to explore the novel phenomena of the coupling system,study the physical mechanism and develop its application potential.Up to now,it has been found theoretically and experimentally that there are various ways of coupling between the magnon and the cavity,such as coherent coupling between the magnon and the cavity.The microwave transmission spectral of the system represents modes repulsion.With the dissipative coupling between the magnon and the cavity,the microwave transmission spectral of the system represents modes attraction.With the indirect coupling of the magnon and the cavity,the microwave transmission spectral of the system can present mode attraction and mode repulsion by adjusting the coupling phase.The study of the physical mechanisms in the magnon and the cavity system paves the way for practical application,and the emerging new phenomena are also the driving force for us to explore the physical mechanisms.The current research in this field is still the tip of the iceberg.For example,we find in our research that,in addition to the above physical mechanisms,the microwave interference effect in the magnoncavity system also affects the microwave transmission characteristics,which will affect the discussion of the physical mechanism of the system and the design application of the device.This dissertation focuses on the YIG-microstrip cavity system and the YIG-copper cylindrical cavity system,and focuses on the microwave interference effect in these systems.We compare the similarities and the differences between the magnon-cavity coupling effect and the microwave interference effect in microwave transmission characteristics experimentally and theoretically.The main work is as follows:(1)We reveal the microwave interference induced microwave transmission in a cavitymagnonic system composed of a yttrium-iron-garnet(YIG)film and a microstrip cavity circuit and analyze the physical factors of the transformation of microwave transmission spectral from mode attraction to mode repulsion.By changing the position of YIG in the circuit,we identify that the magnon in YIG is driven by the standing microwave from the cavity or by the traveling wave through the microstrip.We observe that the microwave transmission spectra show mode repulsion and mode attraction,respectively.The characteristic of mode repulsion can be well described by the coupling between the magnon and the cavity.Without coupling,the mode attraction observed in our experiment can be interpreted by microwave interference between the indirect paths through the cavity and the magnon and the direct path through the traveling wave.We find that mode attraction is caused by the redistribution of the microwave transmission intensity.The phase of the magnon in two cases changes π,which is the key physical factor to understand the change in microwave transmission characteristics.(2)We study the fast-slow light induced by microwave interference in the YIGmicrostrip cavity system.The destructive interference between two types of paths,the direct path through the traveling wave and the indirect paths through the magnon and the cavity,leads to a nearly blocking of microwave transmission when the magnon mode resonates at a particular frequency.This phenomenon is accompanied by a dramatic evolution in the phase of microwave transmission,which strongly adjusts the group velocity of microwave.Tuning the magnon mode crossing the particular frequency by controlling the external magnetic field,the polarity of phase evolution will be reversed,which presents as a switch between phase delay(slow-light)and phase advance(fast-light).In And we experimentally achieve the broadband fast-slow light by tuning the external damping of the magnon.Furthermore,we predict the broadband fast-slow light in different physical parameters.(3)We study the microwave interference effect between antiresonance in the cylindrical copper cavity and the magnon in YIG.The cylindrical copper cavity has a shield effect on the microwave.We place YIG on the microstrip outside the cylindrical copper cavity.On the one hand,it can well shield the coupling between the cavity and the magnon,so that there is only microwave interference effect in this system.On the other hand,the relative phase between magnon mode and antiresonance mode can be adjusted by adjusting the distance between YIG and the cylindrical copper cavity port.By adjusting the relative phase,we find that the microwave transmission spectrum shows mode attraction when the magnon is in-phase with the antiresonance mode;When the magnon and the antiresonance mode are anti-phase,it shows mode repulsion;When the phase is orthogonal,it shows mode crossing.Under all phase conditions,the microwave transmission spectra of the magnon mode and the cavity mode show mode crossing,which proves that there is no coupling between them.Our work further verifies the theoretical model of microwave interference and realizes the phenomenon of mode repulsion based on an uncoupled magnon and cavity for the first time. |
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