| With the fast development of big data and cloud computing,it is demanding to realize the information storage technology with high integration density,low power consumption and high speed read and write.Material systems with perpendicular magnetic anisotropy?PMA?are promising in applications as they could increase the storage density and thermal stability.Ferromagnetic/Ferroelectric?FM/FE?multiferroic heterostructure is a useful way to realize electric-field control of magnetism,and strain-mediated magnetoelectric coupling with large effect at room temperature has been widely studied.A lot of work have been carried out on electric-field control of magnetism in FM/FE multiferroic heterostructures via interfacial strain coupling.However,to date,most of the work focused on the FM films with in-plane magnetic anisotropy,while there have been only a few reports on the FM films with PMA.Moreover,all the previous work on electric-field manipulation of PMA deduced the total magnetic anisotropy change of the system without separating it into the bulk and interfacial contributions.Therefore,electric-field control of the interface magnetic anisotropy,which usually favors the PMA,has not been demonstrated so far.Knowing how electric-field modifies the bulk and interface anisotropy is helpful for deliberately engineering the bulk or interface properties to achieve a certain modification.In particular,the ability to manipulate interface magnetic anisotropy by electric field is essential for manipulating PMA.So electric-field manipulation of interface magnetic anisotropy is highly desired regarding its significance for both fundamental issues and applications in memory devices.In this thesis,we report electric-field control of magnetism of?Co/Pt?3 multilayers involving PMA with different Co thicknesses grown on PMN-PT?011?substrates.The main work can be divided to two parts as follows:Both M-H hysteresis loops and ferromagnetic resonance results demonstate larger Co thickness favors in-plane configuration,which can be understood as the thickness-driven spin reorientation transition?SRT?.Electric-field driven SRT were observed by applying in-situ electric fields for different samples.By phenomenologically separating the interfacial and bulk contributions to the magnetic anisotropy and using the linear fitting,we demonstrate electric-field modulation of the interface magnetic anisotropy for the first time.Besides,electric-field-induced changes of the interface and bulk magnetic anisotropies were separated.Our results show that electric-field modulation of interface magnetic anisotropy plays an essential role in driving the SRT.The electric-field-induced changes of the interface and bulk magnetic anisotropies can be understood by considering the strain-induced weakening of Pt 5d-Co 3d hybridization and increasing of magnetoelastic energy,respectively.Co thickness-driven SRT proceeds through a coexistence phase,and we study the electric-field control of magnetism for the samples with coexistence phase.A one-way magnetization versus electric field?M-E?behavior is observed without external magnetic field,which can be understood by considering the energy barrier between the out-of-plane and in-plane magnetization.We also demonstrate the role of competition between the applied magnetic field and electric field in determining the butterfly-like M-E behaviors.Moreover,we study the domain structures with in situ electric fields for the coexistence phase samples to understand the microscopic mechanisms for electric-field modulation of magnetism.Our results not only demonstrate electric-field control of magnetism by harnessing the strain-mediated coupling in multiferroic heterostructures with PMA,which is significant for understanding the mechanism of electric-field control of magnetism,but also pave the way for electric-field modulations of Dzyaloshinskii-Moriya interaction and Rashba effect at interfaces to engineer new functionalities. |
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