Study On The Fabrication And Magnetoelectric Properties Of PZT/LSMO Multiferroic Composite Thin Films

In this thesis we fabricated PbZro.52Tio.48O3/Lao.67Sro.33MnO3(PZT/LSMO)and PbZr0.52Ti0.48O3/NiFe2O4/La0.67Sr0.33MnO3(PZT/NFO/LSMO)multiferroic composite thin films on(001),(110)and(111)oriented SrTiO3(STO)single crystal substrates by pulsed laser deposition,respectively.We studied the microstructure,magnetic and electric properties,magnetoelectric coupling effect of the multiferroic composite thin films,and the main experimental results are as follows:1.We fabricated LSMO magnetic bottom electrode on(001)orientated STO single crystal substrate by pulsed laser deposition,and the optimal experimental parameters are as follows:substrate temperature is 750 ℃,oxygen pressure is 15 Pa,target substrate distance is 80 mm,laser frequency is 1 Hz,laser energy is 220 mJ,and anneal temperature is 800 ℃.The XRD patterns show the LSMO thin films are grown along the(00l)orientation and are well cryystallized.The AFM images indicate the surface of the thin film is flat with uniform grain size.The magnetic testing results reveal the thin film exhibits ferromagnetic property at room temperature,and the phase transition temperature is about 350 K.2.We fabricated PZT ferroelectric thin film on(001)oriented LSMO magnetic electrode by pulsed laser deposition,and the optimal experimental parameters are as follows:substrate temperature is 600 ℃,oxygen pressure is 10 Pa,target substrate distance is 80 mm,laser frequency is 1 Hz,laser energy is 220 mJ,anneal temperature is 650 ℃.The XRD patterns show the PZT thin films are grown along the(00l)orientation and are well cryystallized.The AFM patterns indicate the surface of the thin film is flat with uniform grain size.The piezoelectric butterfly curve and ferroelectric hysteresis loop reveal the PZT thin film has good ferroelectric and piezoelectric properties.3.Using the optimal experimental parameters above,we fabricated PZT/LSMO composite thin film on(001),(110)and(111)oriented STO single crystal substrates by pulsed laser deposition,respectively.The XRD patterns show all the thin films are grown along the corresponding substrates orientation and are well cryystallized.The magnetic testing results indicate that all the thin films have good ferromagnetic property at room temperature,and the electric testing results show they all have good ferroelectric property.We use Magnetoelectric Coupling Testing System studying the magnetoelectric signal of the composite thin films,the results indicate all of them have magnetoelectric signal,and the values of the signal of different orientation thin films are not the same,particularly the(111)orientation structure obtains the maximize magnetoelectric signal and magnetoelectric voltage coefficient value of about 3.2 μV and 102.86 mV/cmOe,respectively.4.Because the magnetoelectric coupling effect of PZT/LSMO bilayer is weak,in order to enhance the magnetoelectric effect,we insert NFO magnetic layer between PZT and LSMO.Using the optimal experimental parameters above,we fabricated PZT/NFO/LSMO composite thin film on(001),(110)and(111)orientation STO single crystal substrates by pulsed laser deposition,respectively.The XRD patterns show all the thin films are grown along the corresponding substrates orientation and are well cryystallized.The magnetic testing results indicate all the thin films have an increase of magnetic property.The electric testing results show they all have good ferroelectric property.Magnetoelectric coupling testing indicate all the thin films have magnetoelectric signal,the magnetoelectric signal has an increase by inserting NFO layer between PZT and LSMO,particularly the(111)orientation structure obtains the maximize magnetoelectric signal and magnetoelectric voltage coefficient value of about 4.2 μV and 133.3 mV/cmOe,respectively.