Investigation Of The Magneto-optical Properties In Two-dimensional Fe₃GeTe₂ Heterostructures

Spintronics is a subject that studies the spin properties of electrons,which has great application prospect in magnetic-optical memory devices,spin valve,magnetic tunnel junction and so on.Spintronics guides the development of the Post Moorish information industry.In recent years,the discovery of two-dimensional intrinsic magnetic materials has provided better platforms for the study of two-dimensional spintronics.Magneto-Optic Kerr technology has become a powerful method to detect the magneto-optical properties of two-dimensional magnetic materials because of its unique advantages.However,the practical industrial applications have put forward higher requirements on magnetic and optical properties of two-dimensonal ferromagnetic materials.The limited performance of the independent two-dimensional magnetic materials restricted their applications in spintronic devices.By reasonably constructing heterostructures of two-dimensional magnetic materials,various magnetic interfacial effects can be generated,thereby creating opportunities for more abundant and excellent magnetic and optical properties can be obtained.Thus,how to construct two-dimensional magnetic heterostructures with high performance and how to realize the effective magnetic regulation of two-dimensional magnetic heterostructures are one of the most important topics of current spintronics device research.Two-dimensional van der Waals itinerant ferromagnet Fe₃GeTe₂has aroused extensive interests among researchers because of its advantages of larger intrinsic perpendicular magnetic anisotropy,higher Curie temperature,relatively better stability and so on.The magnetic and optical performances of Fe₃GeTe₂ heterostructures are worth studying.In this paper,the magneto-optical response as well as magnetic behaviours of Fe₃GeTe₂heterostructures were studied by Magneto-Optic Kerr system,which lays a foundation for the application of two-dimensional spintronics devices.The main work is listed as following:1.Investigation of magneto-optical properties in Fe₃GeTe₂ on different substrates with different thickness and realization of Curie temperature modulation in two-dimensional Fe₃GeTe₂ by substrates without external field.High quality Fe₃GeTe₂single crystals and thin falkes were synthesised by chemical vapor transport method and mechanical exfoliation.The thickness dependence of magnetism of Fe₃GeTe₂ was obtained by Magneto-Optic Kerr system,which built a foundation for the study of Fe₃GeTe₂heterostructures.Then,Fe₃GeTe₂/Au,Fe₃GeTe₂/Al and Fe₃GeTe₂/Si O₂heterojunctions were prepared and their magneto-optical properties were studied.The results showed that the Curie temperature of Fe₃GeTe₂ was influenced greatly by metal substrates.The Curie temperature of the same thickness for Fe₃GeTe₂ on Au and Al substrates have a difference of about 70 K.Finally,it is concluded that the biaxial stress caused by lattice mismatches and charge transfermation both affected the magnetism of Fe₃GeTe₂ using the First-principle calculations.This work provides a guidance for the modulation of Curie temperature in two-dimensional ferromagnetic materials.2.Realization of magneto-optical enhancement in FePS₃/Fe₃GeTe₂ van der Waals heterostructures.High quality FePS₃ single crystals and FePS₃/Fe₃GeTe₂ van der Waals heterostructures were prepared by chemical vapor transport method,mechanical exfoliation and fixed point transfer technique.The susceptibility measurements of FePS₃in high magnetic field provided a theoretical basis for the analysis of ferromagnetic and antiferromagnetic spin states.Results of Magneto-Optic Kerr measurements showed that the Magneto-Optic Kerr angle was three times bigger,the Curie temperature of Fe₃GeTe₂was improved by more than 30 K and the coercive field was increased by?100%due to the proximity coupling effect between Fe₃GeTe₂ and FePS₃.In addition,the Kerr hysteresis loops of FePS₃/Fe₃GeTe₂/FePS₃ showed that multiple magnetic states appeared in the heterostructures,which may be caused by the pinning effect of antiferromagnetic/ferromagnetic domain.These work indicated that antiferromagnet/ferromagnet coupling is an effective way to strengthen magneto-optical propertiues without any external excitation.It also provides new materials for advanced spintronics and magnetic storage devices.3.Investigation of the exchange bias effect in FePSe₃/Fe₃GeTe₂by Magneto-Optic Kerr measurements.High quality FePSe₃/Fe₃GeTe₂ van der Waals heterostructures were synthesized by chemical vapor transport method,mechanical exfoliation and fixed point transfer technique.The magnetic properties of FePSe₃/Fe₃GeTe₂ after field cooling was studied by Magneto-Optic Kerr techinque.Results showed that the significant exchange bias fields in FePSe₃/Fe₃GeTe₂ were obtained and the block temperature showed an unintrinsic property.The block temperature of the same material changed with the thickness,roughness and coupling strength of the materies.In addition,the long range coupling of exchange bias in the Fe₃GeTe₂ was demonstrated by the magnetic measurements of Fe₃GeTe₂ and FePSe₃/Fe₃GeTe₂.This work indicats that FePSe₃/Fe₃GeTe₂ van der Waals heterostructures have potential application value in spin valve devices.4.Investigation of magnetic coupling enhancement in FePSe₃/Fe₃GeTe₂ van der Waals heterostructures by Magneto-Optic Kerr measurements.The magnetic coupling enhancement of FePSe₃/Fe₃GeTe₂ heterostructures was achieved through laser-shock pressure.The results of Magneto-Optic Kerr mesurements showed that the coercive field and exchange bias field of FePSe₃/Fe₃GeTe₂ were almost doubled under external pressure.With the increasing of external pressure,the block temperature of exchange bias was significantly promoted from 20 K to 110 K(approaching the Neel temperature of FePSe₃).In addition,the long range coupling of enhanced exchange bias and block temperature in the Fe₃GeTe₂ was proved by comparing the magnetic peoperties of FePSe₃/Fe₃GeTe₂ and Fe₃GeTe₂ under external pressures.The above results provide an effective technology to enhance magnetic coupling and further promote its application in high performance spin valve devices.The above work realized the magneto-optical enhancement and magnetic properties regulation of Fe₃GeTe₂ and its heterostructures,which indicated that Fe₃GeTe₂ and its heterostructures are two-dimensional ferromagnetic materials with excellent properties.They will have great application prospects in high-performance magneto-optical memory and spin valve devices.