Research On Magneto-optical Properties Of Ferromagnetic Two-dimensional Material

The emergence of long-range ferromagnetic orders in two-dimensional(2D)ferromagnetic(FM)material provides broad development prospects for magnetic storage,magnetic coding,and photonic chips.The magnetic orders can be switched between FM and antiferromagnetic(AFM)states by magnetic field,electric gating,electrostatic doping and hydrostatic pressure,which empower a pivotal foundation for information transfer by magneto-optical coupling.To date,diverse 2D van der Waals(vdW)FM and AFM metal,insulators and even semiconductors have been explored.FM Cr2Ge2Te6 fewlayer have demonstrated a p-type semiconducting behavior;few-layer FM metal Fe3GeTe2 have shown room temperature Curie temperature(Tc)by ionic gating to enhance carrier densities;magnetic topological insulator MnBi2Te4 have recently been reported to present layer-dependent magnetic phase.However,thus far,few 2D vdW magnets have been revealed luminescence and exciton behaviors,robust magnetic control of micro-lasing is still elusive so far.The PL of CrI₃ derives from a ligand-field-allowed d-d transition,which naturally lead to a very broad PL peak with a FWHM of 100-200 nm owing to strong vibrionic coupling,extremely limiting the potential for magnetooptoelectronic devices.It is difficult to achieve magnetic/electric control of spin in AFM NiPS3,due to a high critical field up to 10 T at least.In this work,CrI₃/microsphere vertical gain structure have designed and fabricated by in-situ transferred method for realizing robust magnetic control of micro-lasing.The lensing and screening effects of SiO2 microspheres enhance coupling between gain area and optical modes,which increase the spontaneous emission efficiency of CrI₃ to create magnetic control and coding of near-infrared(NIR)WGM emission with a full width at half-maximum(FWHM)of?5 nm.This work provides a new idea for creating magnetic encoding micro-lasing for photonic integrated chips.The main research contents of the thesis are as follows:1.The temperature dependence reflective magnetic circular dichroism(RMCD)spectra show that,the Tc of?50 K are observed on both CrI₃/microsphere and bare CrI₃,indicating the SiO2 microsphere cavities do not influence the Tc of CrI₃.2.The experimental results of optical pumping of CrI₃/microsphere show that,the WGM of the SiO2 microsphere cavity enables the CrI₃/microsphere to create a narrow and strong WGM PL with a FWHM of?5 nm.3.Magnetic control of WGM PL emission of CrI₃/microsphere show that,circularly polarized WGM PL features in CrI₃/microsphere are coupled with CrI₃ magnetic orders.The right-handed(left-handed)polarized WGM PL are dominated in a positive(negative)magnetic field of+1 T(-1 T).We studied the multi wavelength magnetic encoding of circularly polarized PL through recycling a loop of magnetic field between+1 and-1 T.Multi-wavelength magnetic encoding is realized through repeatedly manipulating helicity and degree of polarization(DOP)of each WGM PL peak from CrI₃/microsphere.