Preparation And Physical Properties Of CoFeO₃-based Composite Film

With the development of information technology,magnetic materials play an important role in the fields of information storage,microwave devices and optical information technology.CoFe₂O₄ has great research value and broad application scenarics in magnetic storage,magneto-optical devices and composite multiferroic materials and other fields because of its high coercivity field,large magnetostriction coefficient,good chemical and thermal stability properties.However,the experimentally prepared CoFe₂O₄ films have generally small coercivity fields and difficult to tune microstructure,which limits the research and application of CoFe₂O₄.To address these issues,we have investigated CoFe₂O₄ and its composite films by the high magnetic field-assisted pulsed laser deposition(MF-PLD),the conventional pulsed laser deposition(PLD)and the chemical solution method(CSD).1.The CoFe₂O₄ thin films with(111)-prefered orientation on(001)-oriented Si wafers prepared by the high magnetic field-assisted pulsed laser deposition(HMF-PLD)system,and the regulation of grain size,stress state and microstructure of CoFe₂O₄ thin films was achieved by changing the magnetic field during the deposition process.The magnetic coupling between the grains is changed due to the change in the grain size and the columnar structure of the film.The thin film prepared under the 0.7 T shows the largest HC value of 6 kOe.2.The CoFe₂O₄/La0.7Sr0.3Mn03/CoFe₂O₄ sandwich layer structure composite films were prepared by PLD.The composite film from rigid coupling to decoupling with increased thickness of the La0.7Sr0.3MnO₃ intermediate layer.Compared with the single CoFe₂O₄ layer,the introduction of La0.7Sr0.3MnO₃ layer enhaeces the magnetic properties.3.CoFe₂O₄/La0.7Sr0.3MnO₃ composite films with different individual La0.7Sr0.3MnO₃ were prepared using the CSD.The magnetic interaction between the grains of the composite films is affected by both the grain size and the quality of the soft-hard magnetic interface.Increasing the annealing temperature during film preparation,the growth of single-domain-sized grains in the hard magnetic phase,and also the elimination of defects at the interface.Thus,the increase in annealing temperature enhances the rigid coupling in the composite and improves the properties of the films.The composite films can reach a maximum coercivity field of 8.27 kOe at room temperature and a maximum magnetic energy product of 2.4 MG Oe.4.CoFe₂O₄ is compounded with La0.7Sr0.3MnO₃ in different molar ratios for the compounded film.On the one hand,since CoFe₂O₄ is an insulating phase,the electron attempt penetration effect will enhance the magnetoresistance of the film.On the other hand,at the interface of CoFe₂O₄ and La0.7Sr0.3MnO₃,the magnetic moments of Mn elements tend to be in opposite arrangement with those of Co elements,which is favorable to the ferromagnetic metallic state transition of the La0.7Sr0.3MnO₃ layer phase near the interface,and according to the percolation model,it is favorable to increase the magnetoresistance transition temperature in the film.For the composite film with 50%molar share of CoFe₂O₄,the low-field magnetoresistance LFMR=19%at 200 K.5.By preparing BiFeO₃ thin films under magnetic field,the microstructure of the films was changed to columnar growth.With the increase of magnetic field,the grain size of the films increases firstly and then decreases,while the growth of grains and the reduction of interfaces and defects are favorable to the enhancement of ferroelectricity.The columnar microstructure of the films prepared under magnetic field will the enhancement of the piezoelectric properties of the enhanced films.The application of magnetic field assisted pulsed laser deposition(MF-PLD)technology is extended for.In summary,the magnetic properties of CoFe₂O₄ and its composite films were improved through the adjustment of preparation parameters,and enhanced magnetoresistance effects were obtained in the corresponding composite films,expanding the application of magnetic fields in sample preparation.