Electric Field-mediated Magnetic Property Of Ferromagnetic Thin Film

With the development of the information storage,the magnetic random access memory with low-cost,high-performance and non-volatile is required.When the electric field with high efficiency and low dissipation,instead of magnetic field and electric current,is directly applied in the magnetic material,the weak magnetoelectric coupling is obtained.This is a critical problem for electric field-mediated magnetism that how to improve the intensity and efficiency of intrinsic magnetoelectric coupling and realize long-range interactions of electric field in ferromagnetic/ferroelectric?FM/FE?system.In this thesis,the magnetic thin film was deposited on single-crystalline substrate PMN-PT(Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃)by magnetron sputtering and molecular beam epitaxy?MBE?.We have investigated the electric field-mediated magnetism mechanism by static and dynamic,and electrical transport measurement.The main results were as following:?1?The magnetism and multi-state memory mediated by piezostrain effect was realized in FM/PMN-PT heterostructure.The magnetic anisotropy was mediated by piezostrain effect.By two different types of applied electric field,the asymmetric bipolar sweeping of electric field and the continuous application of an in-plane lateral electric field during cooling process,the butterfly behavior of magnetism changing with electric field have been transformed into hysteresis loop behavior of that,realizing the non-volatile multi-state memory by applying electric field pulses.?2?The magnon-driven spin screening effect at the interface of FM/PMN-PT heterostructure was found.The FM thin film with in-plane uniaxial magnetic anisotropy was deposited on PMN-PT substrate by magnetron sputtering.When inserted Ta?10 nm?thin film into the interface of FM/PMN-PT heterostructure,the butterfly and volatile behavior was exhibited,which can be resulted from the pure piezostrain effect.When the Ta layer was removed,the magnetism changing with electric field exhibited non-volatile behavior,demonstrating the introduction of charge effect.The interaction length of tranditional charge effect is angstrom order of magnitude,while in this system,the thickness of ferromagnetic thin film is nanometer order of magnitude.Considering magnetic interaction and spin diffusion,magnon-driven spin screening effect was present.?3?The magnon-driven spin screening effect at the interface of FM/PMN-PT heterostructure was verified.The loop behavior of ferromagnetic resonance field and saturation magnetization changing with electric field was obtained in the single-crystalline ferromagnetic thin film expitaxially grown on the PMN-PT substrate,which is consistent with charge effect-induced magnetic change.Considering the complexity of the two-fold symmetry including strain anisotropy and surface anisotropy,the linear change of the four-fold symmetry magnetic anisotropy field,relating to the single–crystal cubic magnetocrystalline anisotropy of the ferromagnetic thin film,was resolved and quantified to exert a magnon-driven,strong direct magnetoelectric effect on the interface of single–crystal multiferroic system,which is related to the loop behavior of saturation magnetization changing with electric field.Therefore,the magnon-driven spin screening effect was verified by single-crystal FM/PMN-PT heterostructure.?4?The long-range spin screening length is obtained.The single-crystal magnetic thin film with different thicknesses?nanometer magnitude?was deposited on PMN-PT substrate by MBE.The loop behavior of ferromagnetic resonance field is inconsistent with the butterfly symmetry behavior induced by piezostrain effect,and the ferromagnetic thin film's thickness is nanometer magnitude,which demonstrated the spin screening effect-dominanted magnetoelectric coupling.Moreover,the spin diffusion length of the epitaxial ferromagnetic thin film is obtained from the results that the change of the cubic magnetocrystalline anisotropy field under different electric fields varies with Fe thickness.Therefore,the long-range interaction of magnon-driven spin screening effect is achieved in FM/PMN-PT heterostructure with different thickness of ferromagnetic thin film.