First-principle Study On The Electronic Structures And Optical Properties Of Y_1-xSr_xCu_1-yMn_ySO System And Experiments

Diluted magnetic semiconductors have the dual properties of spin and charge,which are material basis for synthesizing spin optoelectronic devices and are of great significance for the information transmission,processing and storage capacity.The new types of diluted magnetic semiconductors based on iron-based superconductors achieve independent charge and spin regulating and controlling.In this dissertation,the electronic structure and optical properties of Y_1-x-x Sr_xCu_1-yMn_ySO system are discussed mainly by CASTEP module in Material Studio based on the first-principles calculation of density functional theory.The structural model,the electronic structure and optical properties?absorbance index,reflection coefficient and dielectric constant?are studied.In addition,(Y_1-xSr_x)(Cu_0.925Mn_0.075)SO polycrystalline samples are synthesized by solid state method.The samples are investigated by XRD,low-temperature electric resistivity,magnetic properties and PL spectrum measurements,which lay a solid foundation for preparing new diluted magnetic semiconductors with perfect properties in(Y_1-xSr_x)(Cu_0.925Mn_0.075)SO system.The detail is as follows.1.The parent YCuSO is calculated at first by first-principle method for good reliability and optimal structure.Then the electronic structure and optical properties are calculated.There are two obvious peaks in the curve of absorption index and reflection coefficient,sited at 146.5nm and 90.8 nm,respectively.The static dielectric constant of parent YCuSO is 7.1.2.In case of the two-site doping system(Y_0.75Sr_0.25)(Cu_0.75Mn_0.25),Sr ion substituted for Y ion produces charge and Mn ion for Cu ion produces spin.Thus 2×1×1 super lattice is constructed,the optical structure is found out,and the band structure and density of states are calculated with taking spin account of.At last the optical properties are discussed.The reflection peak of(Y_0.75Sr_0.25)(Cu_0.75Mn_0.25)locates at 123.5nm?about96%?.The absorption peaks are at 70.7nm?2.6×10³/cm?and 168.8nm?1.8×10⁵/cm?.The static dielectric constant is 5.2.3.As for(Y_0.875Sr_0.125)(Cu_0.875Mn_0.125),all the calculation mehtod is the same as(Y_0.75Sr_0.25)(Cu_0.75Mn_0.25)except that 2×1×1 super lattice is constructed.The reflection peak of(Y_0.75Sr_0.25)(Cu_0.75Mn_0.25)SO locates at 100.0nm?about 76%?.The absorption peaks are at 66.0nm?1.2×10⁴/cm?and 138.9nm?2.2×10⁵/cm?.The static dielectric constant is 6.3.By comparison,both the reflection peak and absorption peaks are red-shifted and the static dielectric constant decreases when doping.4.By experiment,we synthesize(Y_1-x-x Sr_x)(Cu_0.925Mn_0.075)SO?x=0,0.05,0.075,0.1?polycrystal samples by solid state method.The crystal parameters a and c increase with Sr ion dopant addition.It can be found out that the low-temperature-electric resistivity exhibits the character from semiconductor to metal with the dopant increasing.It shows in magnetization curve that the samples are probably new diluted magnetic superconductors when x=0.05 and 0.1,and the FWHM increases while the intensity decreases with the Sr dopant addition by photoluminescence spectra.