Regulation Of Magnetoelectric Properties Of Li(Mg/Cd)P-based Dilute Magnetic Semiconductors

Diluted magnetic semiconductors(DMSs) are considered as a key material of a new generation of spintronic devices,because they combine the charge freedom and spin freedom of the electrons in the same matrix and have both advantages of semiconductor and magnetic materials.The new electronic devices and functional devices with small volume,low energy consumption,ultra-high speed,less heat can be designed and prepared using to their various characteristics,which can bring revolutionary progress in the field of information technology and materials.Therefore,DMSs have attracted much attention in recent years.Recent studies have found that ?-?-? LiMgP-based and LiCdP-based novel dilute magnetic semiconductors not only have the dual properties of spin and charge,but also overcome the limitation of solid solubility for magnetic ions in traditional dilute magnetic semiconductors,which provides a direction for the preparation of novel dilute magnetic semiconductor materials with Curie temperature higher than room temperature.In this dissertation,the first principles calculation method is used to study the magnetoelectric properties of Ni,Fe doped LiMgP systems and Fe doped LiCdP system;Then,Fe-doped LiCdP polycrystalline samples are prepared by solid-state reaction method,and their structures and magneto-electric properties are measured and analyzed.The main work and conclusions are listed as follows:(1)Firstly,the magnetoelectric properties of Fe doped LiMgP new diluted magnetic semiconductor with different ion concentration ratio are studied by using the first principles calculations.The results reveal that Fe-doped LiMgP is an outstanding half-metallic ferromagnet with large half-metallic energy gap and controllable electromagnetic properties.For pure LiMgP system,the chemical bonds are polarized covalent bonds,and Fe doping lead to form stronger Fe-P covalent bond than that of Mg-P.When Li is excessive,the formation energy is the lowest and the structure is the most stable.The value of band gap decreases obviously compared with that of Fe only,and the half-metallicity is weakened.The overlapping charge distribution of Fe-P bonds and the net magnetic moment of the system are the smallest.When Li is insufficient,the system becomes metallic ferromagnetism.The overlapping charge distribution of Fe-P bonds reaches the maximum value of 0.78,the bond length reaches the minimum,and the net magnetic moment of the system is the biggest.(2)Moreover,the magnetoelectric properties of Li(Mg,Ni)P new diluted magnetic semiconductor are also studied by using the first principles calculations.The results show that the Ni doped LiMgP system has a half-metallicity,and sp-d orbital hybridization occurs.The magnetic and electric properties can be controlled by adjusting the concentrations of Fe and Li,respectively.When Li is insufficient,the half-metallic energy gap of the system is the widest and the net magnetic moment is2.78?_?.When Li is excessive,the system exhibits metallic properties.On the optical properties,after doping Ni atom,a new peak appears in the low energy region of the imaginary part of the dielectric function,the complex refractive index function and the absorption spectrum.These results show that the incorporation of Ni expands the absorption range of electromagnetic wave and the reaction range of photo-conductivity of the system.And the optical absorption spectrum of the also shows the characteristics of obvious blue shift after doping Ni atom.(3)Finally,the magnetoelectric properties of Fe-doped LiCdP systems are also studied.The first principles calculation results show that Li(Cd,Fe)P system has obvious spin polarization phenomenon,the net magnetic moments are found in the doping systems of various concentrations,and Li-excess system shows the half-metallicity.Moreover,the Fe-doped LiCdP bulk samples are prepared by the solid-phase reaction method.the property characterization find that Fe-doped LiCdP system has magnetic properties,and the incorporation of Fe no change the crystal structure and space group of the samples.The lattice parameters of the samples ares in good agreement with the theoretical calculation results,and the lattice parameters decreases with the increase of doping concentration.The resistivity of Li(Cd_1-xFe_x)P decreases with the increase of temperature,and the sapmple exhibits a semiconductor behavior.The experimental and calculation results show that the introduction of Fe atoms in the LiCdP system can improve the conductivity of the system.The magnetic phase transition temperature of Li(Cd_0.92Fe_0.08)P can reach 260 K,and the coercivity can reach 538 Oe.The maximum saturation magnetic moment of the sample increases with the increase of sample concentration.