Magnon-induced unidirectional spin Hall magnetoresistance in ferrimagnetic insulator $Gd_3Fe_5O_{12}$

Abstract

Spintronics suggests one of the way to go to destination of next generation-low energy consuming device, by applying spin information of electron to various device. In this dissertion, we optimize the deposition condition of compensated ferrimagnet which make possible to research on ferrimagnetic dynamics. Firstly, We suggest the optimization condition of $Gd_3Fe_5O_{12}$ sample which is suit on observing ferrimagnetic dynamics. Ferrimagnet is consist of two different magnetic moment which are antiferromagnetically coupled. As Ferrimagnet have similar magnetic structure to antiferromagnet with net moment involving easier control, research on ferrimagnetic dynamics become one of the most important topics in spintronics. This dissertation aims for how compensation point of ferrimagnet affects to ferrimagnetic magnon spin, and introduce the progress on selecting, fabricating and optimizing condition for that goal. We investigated magnon spin measurement of ferrimagnetic alloy ‘Cobalt Gadolinium’, and experimentally confirmed that ferrimagnetic insulator is suit on applying to ferrimagnetic dynamics research. We optimized depositing condition of ferrimagnetic insulator $Gd_3Fe_5O_{12}$ using Metal Organic Decomposition which is relatively simpler than common method. We also checked the magnetic damping of sample and confirmed that our sample is suit on researching ferrimagnetic dynamics. Furthermore, we aimed to investigate the influence of temperature on the unidirectional spin Hall magnetoresistance in $Gd_3Fe_5O_{12}$ | Pt. We investigated how compensations of ferrimagnet affects the magnon induced signal such as unidirectional spin Hall magnetoresistance. From the result, we estiamate that the unidirectional spin Hall magnetoresistance in the ferrimagnetic insulator is determined by the lowest-energy magnons of the ferrimagnetic state. We expect the possibility that the temperature dependence of magnons in the ferrimagnetic state may impact various signals measured by magnons, such as unidirectional spin Hall resistance. After all, we’ve investigated the measurement of unidirectional spin Hall magnetoresistance of $Gd_3Fe_5O_{12}$ | Pt system with various temperature passing through compensations. in order to observe how magnon inversion across compensation affect to magnon driven signal such as unidirectional spin Hall magnetoresistance. We found that that sign of unidirectional spin Hall magnetoresistance follows the magnon mode of ferrimagnet with lowest energy. This result indicates that the temperature dependent magnetic dynamics of ferrimagnet acts on various signal originated from magnon spin.