Studies On The Epitaxial Growth And Magnetic Properties Of H-LuFeO₃ Thin Films

Recently,weak ferromagnetic ordering and ferroelectricityhave been found in h-LuFeO₃ at roomtemperature.This new type of ferrites has attracted considerable attention because of their unique physical characteristics andpotential applications.However,the ferromagnetic ordering of h-LuFeO₃ is determined below 120 K.We know that the ferromagnetic ordering at the low temperature below room-temperature is difficult to meet the practical application.Therefore,how to improve the ferromagnetic properties and increase the anti-ferromagnetic transition temperature to room temperature is the key to realize the application of h-LuFeO₃ in the magnetic and electrical devices.The epitaxial growth of thin film is the basis to investigate the properties of h-LuFeO₃.In this dissertation,firstly,the hexagonal LuFeO₃（h-LuFeO₃）thin films were epitaxially grown on YSZ（111）substrates by pulsed laser deposition method.Then,the magnetic properties of high-quality epitaxial h-LuFeO₃ thin filmswere investigated.The main contents and results are as follows:（1）LuFeO₃ ceramic target with single composition and high density was prepared by solid phase reflection sintering method.And then the h-LuFeO₃ films were prepared by pulsed laser deposition method.The effect of fabrication parameters on the growth of h-LuFeO₃ epitaxial films were investigated preliminarily.（2）The effects of pulsed laser deposition parameters on the growth of h-LuFeO₃ thin films were systematically investigated.The quality of the films was studied by changing the substrate temperature,oxygen pressure and laser energy.The optimum parameters were obtained,that is,the substrate temperature is 750 oC,the oxygen pressure is 20 mTorr,the laser energy is 400 mJ and the laser repetition rate is 10 Hz.The thin filmsgrown at the optimal parametersare single phase h-LuFeO₃ with c axis-orientation,and have a relatively smooth surface and abrupt interface.We can obtaine the epitaxial relationships between the film and the substrate from the TEM and SAED,whichareh-LuFeO₃（0001）//YSZ（111）andh-LuFeO₃[100]//YSZ[210].（3）The magnetic properties of h-LuFeO₃ epitaxial films were characterized by SQUID.The results show that both the saturation magnetization and the coercive field of the films increase with the decrease of the test temperature.This is because the magnetism ofh-LuFeO₃ is mainly derived from Fe.With the decrease of temperature,the magnetic moment of Fe ions grows up,thus showing a monotonic increase of macroscopic magnetization.The magnetic properties of h-LuFeO₃ films originate from the exchange of Fe atoms in the crystal,which are affected by the lattice distortion of the films.Therefore,the lattice distortion of the films with different thicknesses directly influences the magnetic properties of the films.