Modulation Effects Of Electric Field On Physical Properties In "Ferromagnetic/Ferroelectric" Heterostructures

With the continuous development of technology, multiferroic materials have received a great deal of interest and research activities for their rich physical properties and the miniaturization of the device. The magnetoelectric effect of single-phase multiferroic materials is very weak, and most of them can be only observed at low temperature. People found that magnetoelectric (ME) composites can avoid these disadvantages and possess higher magnetoelectric coupling coefficient. In order to obtain greater magnetoelectric effects, people tend to consider the ferromagnetic/ferroelectric (FM/FE) heterostructures to promote the practical application of multiferroic materials by raising the magnetoelectric coupling effect at room temperature. In this thesis, modulation effects of electric field on physical properties in "ferromagnetic/ferroelectric"heterostructures were studied. The main investigations were summarized as follows:Firstly, La0.6Ca0.4MnO3/Pb(Zr0.52Ti0.48)O3 (LCMO/PZT) thin film was prepared by sol-gel method and spin-coating technology. The effective modulation effects of the electric field on Curie temperature (Tc), as well as the magnetization of LCMO/PZT composite, were obtained by applying an electric field to the ferroelectrics. Tc changed about 3 K when electric field was applied. Obvious converse magnetoelectric effect (denoted as the relative change in magnetization, Δ M～15%) at 200 K and E=10 kV/cm, as well as large electroresistance effect (the relative change in resistance, ER～61%) at 77 K and E=-4 kV/cm, has been obtained in LCMO/PZT thin film.Secondly, we investigated the effects of electric field on the magnetization and electric transport properties n La0.6Ca0.4MnO3/Pb(Mg1/3Nb2/3)03-PbTiO3 (LCMO/PMN-PT) thin film prepared by pulsed laser deposition technology. The manipulations of magnetic and electric properties have been well achieved by applying an ex situ electric field(Eex) on to ferroelectric phase in ferromagnetic-ferroelectric heterostructures. The polarization switching of FE substrate induced by an Eex can induce both a magnetic field shift (δH=1250 Oe at Eex=1kV/cm) at 200 K when the magnetization is 72 emu/cm3. Furthermore, obvious electroresistance effect has been obtained in LCMO thin film.Lastly, Ni/PMN-PT(001) multiferroic heterostructures were prepared by pulsed laser deposition technology. Converse magnetoelectric effect in different conditions, including electric field, temperature and bias magnetic field, was investigated. We demonstrated the non-volatility, reversibility, and temperature stability of the modulation effect on magnetic properties by electric field at room temperature. Large non-volatile coercivity shift of up to 23.2%, as well as non-volatile remanent magnetization difference of up to 50.1% at room temperature, was obtained. Moreover, this non-volatile tuning of magnetic properties also persists over a broad range of temperature. Besides, non-volatile, reversible magnetization switching by impulse electric field is achieved near the coercive magnetic field.