Effect Of Growth Mode Of Magnetic Nanoparticle Film On Microstructure And Magnetic Properties

With the rapid development of digital electronic industry and information technology,magnetic nanoparticle material has been widely used as an important nanostructured material in such fields as high-density storage,targeted therapy and high-resolution magnetic resonance imaging.Unlike bulk materials,the unique size effect of magnetic nanoparticle materials makes many of its physical parameters change at the nanoscale,so its physical properties are also complex and diverse.The physical properties of magnetic nanoparticle films are closely related to their composition,structure,particle size and ambient temperature.With the continuous miniaturization and integration of magnetic electronic components,the size of the magnetic particles is continuously reduced,thus causing two important problems:(1)the Curie temperature drops sharply as the particle size decreases;(2)the superparamagnetism causes the magnetic moment instability increases.Due to the different physical properties required in different applications,it is of great importance to achieve the size controlling and regular distribution of magnetic particles to improve material properties and stability.It is particularly important to find a way to control the structure and particle size of the magnetic nanoparticle composite films.The particles can be evaporated directly from the source materials onto the substrate to form a film without chemical reaction,and plasma discharge with the method of vacuum thermal evaporation.The structure of films can be controlled directly by controlling the source material type,evaporation sequence,evaporation rate and substrate temperature.In this paper,two kinds of source materials with different surface energy were selected for vacuum thermal evaporation,and the well-arranged magnetic nano-particle composite film was successfully prepared.The size and regulation of the magnetic particles can be controlled by controlling the thickness of the magnetic layer and the method of composite layer growth.Futhermore,the magnetic and electrical properties,crystal structure and surface morphology of the films were examined to determine the corresponding relationship between the structure and the performance of the magnetic film.A feasible method for preparing a magnetic nano-particle film with small size,well-arranged and good performance was given.In this paper,co-deposition of nano-particle film,multi-layer nano-particle film and composite layer growth of nano-particle film were prepared by three kinds of preparation methods:co-deposition,layer growth and composite layer growth.The main conclusions are as follows:(1)The effect of SiO on Co films and the influence of high magnetic field on the structure and magnetic properties of Co-SiO and Fe20Ni80-SiO structure were investigated.The results are as follows.For Co-SiO film,the growth mode of the film changes obviously after doped with SiO.The reason why the Co thin film changes from columnar growth to insulating medium encapsulates magnetic particles is that the surface energy of SiO is much lower than Co,and the application of high magnetic field does not change the structure of granular film obviously.In addition,the granular structure reduces the saturation magnetization of the film,and both the application of SiO and a high magnetic field can affect the surface morphology of the sample.For Fe20Ni80-SiO films,the highmagnetic field refines the surface grains and the grain size of the film,which in turn affects the magnetic properties of the film.(2)The effects of high magnetic field on the microstructure and magnetic properties of multi-layered Fe20Ni80-SiO multilayer films were investigated,and the effects of different modulation periods on the microstructures and magnetic properties of multilayer films were investigated.The results show that the alternating deposition of multilayers can also form a thin film structure of spherical shell structure with non-magnetic media wrapped in magnetic medium,while the application of high magnetic field does not change the structure of the thin film but decrease the size of magnetic particles.XPS results show that the ingredient of film is uniform,proving the feasibility of this method.In addition,the TEM results of the magnetic multilayers with different modulation periods show that the obvious spherical shell structure can be formed when the thickness of the magnetic layer is 3 nm.At this time,the saturation magnetization reaches 419 emu/cm3.(3)The efect of substrate temperature on the structure and magnetic properties of co-deposited Fe20Ni80-SiO particles was studied,and the positive effect of substrate temperature on the film structure was confirmed.The magnetic nanoparticle composite film with neatly arranged particles and good magnetic properties was successfully prepared by co-depositing Fe20Ni80 With SiO and alternately depositing the SiO barrier layer,and the magnetic particles with small size were also found to have good magnetism.The microstructure of the composite magnetic nanoparticle film shows that the film has uniform structure and neatly distribution prepared by this method.Meanwhile,the saturation magnetization also increases from 198 emu/cm3 to 395 and 374 emu/cm3 when the magnetic particles become neatly arranged.The Velox DPC multi-signal scanning technique was further used to detect the magnetic induction of the nanoparticles.It was found that the transition from single to multi-domain was accompanied by the magnetic transition from continuous film to uniform granular film.