The Preparation And Properties Of Magnetic Feq₃ And Mnq₂ Micro/nano Crystals

With the increasing demands for low-weight,large-area,flexible and environmentally friendly electronics,organic materials and devices have received worldwide attention.Organic materials have the advantages of simple preparation process,great in variety,soft lattices,adjustable properties and biocompatibility,and have been widely used in organic light-emitting diodes(OLED),field-effect transistors(OFET),organic solar cells and organic sensors.In recent years,people have also found that organic semiconductor materials have extremely long spin relaxation times and great potential in the field of spintronics.It is expected that the preparation of spintronic and optoelectronic devices with semiconductor functions will be realized by using organic materials.Despite the great advances made in these years,there are still some problems in the field of organic spintronics.For example,although the organic semiconductor materials have weak hyperfine interaction and spin orbit coupling,which results in very long spin relaxation times,the spin diffusion lengths obtained in experiments are far shorter than that of the theoretical expectation.Up to now,large magnetoresistance effect can only been found at low temperatures,which greatly restricts the application of organic spintronic devices.One possible reason is that the electrical conductivities between the organic semiconductor materials and ferromagnetic materials don't match.In order to solve this problem,we tried to study the organic magnetic materials,that is,to study the organic semiconductor materials with the ferromagnetic properties.According to the previous literatures,ferromagnetic organic materials can be achieved through transition-metal doping.However,the problem of magnetic clusters is hard to exclusive,which makes the origin of the ferromagnetism become uncertain.In this paper,we propose to prepare micro/nano crystals of magnetic 8-hydroxyquinoline-based molecules,tris(8-hydroxyquinoline)iron(Feq3)and bis(8-hydroxyquinoline)manganses(Mnq2),and study their optical and magnetic properties.Ferromagnetic properties were observed at room temperature.Our results will be benefit for the development of multi-functional organic spintronic devices with photonic,magnetic,and electronic properties.In this thesis,the main contents and conclusions are as follows:1.Feq3 nanostructures including particles and rods with uniform shapes and sizes have been prepared by vapor diffusion method.The lengths and diameters of Feq3 particles are around 9 ?m and 3 ?m,respe-ctively,with an aspect ratio(L/W)around 3.The lengths and diameters of rods are around 20 ?m and less than 1 ?m,respectively,with an aspect ratio(L/W)more than 20,and the rods have hexagonal cross section.The XRD spectra reveal that the particles and rods have good crystallinity.FTIR spectra of Feq3 particles and rods demonstrate that there is no phase change during the formation of the Feq3 nanostructures.The formation mechanism of the Feq3 nanostructures has been analyzed.Most importantly,ferromagnetic behaviors of Feq3 rods have been observed at room temperature.The saturation magnetization is about 10'5 emu,and the coercive field is about 40 Oe.?.Feq3 nanorods with different shapes and sizes have been prepared by using solution method with the assistant of surfactant CTAB.The lengths and the sizes of the Feq3 nanorods are influenced by the concentration of solution and surfactant.All of the rods have hexagonal cross section.The FTIR and XRD spectra show that the rods have good crystallinity and there is no phase change during the formation of the Feq3 nanorods.Magnetic measurements show that the Feq3 nanorods exhibit ferromagnetic behavior at room temperature,and the saturation magnetization and coercive field are about 3.5×10-6 emu and 65 Oe,respectively.?.By vapor diffusion method,we have obtained a series of bis(8-hydroxyquinoline)manganses(Mnq2)crystals with different shapes and sizes by changing the concentration of chloroform solution.The surface topographical features were characterized by SEM.The XRD spectra reveal that the crystals have good crystallinity.The absorption spectra of Mnq2 crystals were analyzed by dual-beam UV-Vis spectrophotometer.The PL spectra of Mnq2 crystals show that the luminescence peak of Mnq2 crystals belongs to the range of green light.The AGM test shows that the Mnq2 crystals exhibit room temperature ferromagnetism.