| In recent years,magnetic nanoparticles have attracted wide attention because of their unique and excellent magnetic properties.The transition metal-based magnetic nanoparticles,ε-Fe2O3 andε-Co,are particularly prominent.Both of them have special crystal structure,for which pureε-Fe2O3 has huge coercivity of 2T at room temperature and large sizeε-Co magnetic nanoparticles are expected to form Skyrmions.Based on the excellent magnetic properties of magnetic nanoparticles,the granular films formed by magnetic nanoparticles will possess the magnetic properties of the particles themselves,which can be applied to magnetic recording,electromagnetic wave absorption and so on.ε-Fe2O3 andε-Co can be synthesized by chemical method,but it is still a technical problem to synthesize pureε-Fe2O3 phase and large sizeε-Co magnetic nanoparticles.In this paper,the synthesis methods ofε-Fe2O3 andε-Co magnetic nanoparticles were studied,and a new preparation method ofε-Fe2O3 magnetic nanoparticle films was explored.Sol-gel method is the most commonly used method for preparingε-Fe2O3.The sol-gel process is used to prepare colloid containing Fe and Si,and then heat treatment is used to form theε-Fe2O3 magnetic nanoparticles coated with mesoporous Silicon.The preparation method is simple,and the pureε-Fe2O3 magnetic nanoparticles with coercivity of 2T can be obtained.In this paper,ε-Fe2O3 magnetic nanoparticles were successfully prepared by sol-gel method,and the effects of different annealing temperature and holding time on the formation ofε-Fe2O3phase were investigated.The optimum annealing temperature is 1100℃and the holding time is 3h.This paper analyses and tries to solve the problem of"waist collapse"of particle hysteresis loops.It is proved by experiments that iron-cobalt alloy phase coating can not effectively solve the problem.Moreover,a dispersed and stable magnetic fluid,the suspension ofε-Fe2O3magnetic nanoparticles,has been successfully prepared.The suspension ofε-Fe2O3 magnetic nanoparticles can still maintain its high coercivity.ε-Co is a special Co phase of cubic structure.Its magnetic nanoparticles vary in size from several nanometers to tens of nanometers.Because of the non-centrosymmetric crystal structure ofε-Co,there may be a DM（Dzyaloshinsky-Moriya）Interaction in the crystal,which makes it possible to produce skyrmions after the formation of large size（Greater than 200nm）particles.Thus it can be used in magnetic storage and spintronics devices.ε-Co is usually obtained by thermal decomposition of[Co2（CO）8].In this paper,ε-Co magnetic nanoparticles of cubic structure were successfully prepared by thermal decomposition of[Co2（CO）8].And the maximum particle size is about 60 nm.After the preparation of high-performance magnetic nanoparticles,this paper explores the feasibility of using Matrix-Assisted Pulsed Laser Evaposition（MAPLE）and magnetic nanoparticles as target materials to prepare magnetic nanoparticle films.For the long preparation period of theε-Fe2O3 magnetic nanoparticles and the small amount of sample,the parameters of the preparation of the granular film are explored first.The deposition of the magnetic nanoparticles with the size and morphology of similar Fe3O4 is carried out to obtain the optimal parameters.In the process of depositing Fe3O4 magnetic nanoparticles,films with thickness ranging from 20 to 500 nm were obtained.The film thickness is positively correlated with deposition time and laser energy.Fe3O4 phase in the film has completely transformed into other phases.The growth trace of particle film can be observed only under the deposition conditions of 5 cm deposition distance,20 mTorr vacuum and 395 u/ns laser energy.Therefore,it is considered that these parameters are the optimum deposition parameters,and it is most possible to prepare magnetic nanoparticle films under these conditions.Then,based on the optimal deposition parameters,two different substrates（single crystal silicon wafer and STO）were used to deposit the magnetic nanoparticles ofε-Fe2O3.It was found thatε-Fe2O3 phase disappeared and the magnetic properties were greatly reduced.The results show that the thermal phase transformation of nanoparticles after MAPLE can not maintain the original structure.At the same time,due to thermal melting and inelastic collision,the original morphology of nanoparticles can not be maintained on the surface of the substrate. |
