| Magnetoelectric heterostructure with ferroelectric,ferromagentic and the coupling properties have atrracted a lot of interests due to the easily achievable E-field-controlled magnetization at room-temperature and thus potential applications in sensors and information storage.Therein,the ferroelectric substrate with high piezoelectric performance and ferromagnetic thin-film with strong magnetoelastic response play the crucial roles in achieving practical E-field-controlled magnetization.The Rhombohedral PMN-PT single crystal with high piezoelectric performance and ferromagnetic CoFeB film without magnetocyrstalline anisotropy have been selected as the ideal combination.The PMN-PT with different orientations shows varied polarization swtiching path under the external E-field,which can be used for realizing different mode of E-field-controlled magnetization.Normally,the(001)-cut or(011)-cut PMN-PT is widely used in such applicatons,while we herein miscut the(001)-cut PMN-PT to acquire the predetermined polarization domain structure.Based on this design,the 109° polarization switching under the external E-field is easily achieved and thus produces a large anisotropic in-plane strain which would be transferred to modulate the film magnetization.This paper consists of four chapters.The fist chapter introdues the relavant knowleges;the second chapter is the charaterization of polarization domain in the miscutted PMN-PT and the investigation of external E-field stimulied in-plane strain-response;the third chapter is the exploration on E-field-controlled magnetization in CoFeB/miscutted PMN-PT magnetoelectric heterostructure;the last chapter is the conclusion of this thesis and envision for future application.The first chapter describes the relevant knowledge and exploration development of multiferroic materials and magnetoelectric heterostructures,also introduces the basic knowledge of ferrolectric PMN-PT substrate and ferromagnetic CoFeB film.Firstly,we roughly introduce the physical mechanism,material system of mutliferroic ferroelcectics and its application in information storage.We also introduce the magnetoelectric coupling mechanism and E-field-controlled magnetization patterns in magnetoelectric heterostructure.Next,we introduce the structure,properties and polarization switching paths of PMN-PT.Subsequently,we show the research developments of E-field-controlled magnetization in magnetoelectric heterostructures with(O01)-cut or(011)-cut PMN-PT ferroelectric substrates.The last part lists the contents of this thesis.The second chapter describes the PMN-PT miscut process,and the polarization switching and the in-plane strain response under external E-field for the miscutted PMN-PT.Firstly,we explain the PMN-PT miscut process and reckon its corresponding polarization domain structure.Next,we use the Polarized Light Microscopy(PLM)and X-ray Reciprocal Mapping(RSM)to analyze the polarization switching pattern in the miscutted PMN-PT,and reveal that 109° polarization swtiching as much as～90%exists in the E-field reversal process.Lastly,we exhibit the home-made strain monitor device which is subsequently used to in situ monitor the in-plane strain-E-field curve along[110]and[1-10]directions.A relatively large anistropic strain with remnant strain appears in our results.The succeeding analysis indicates that it is the 109° polarization switchign under external E-field induce the rotation of in-plane strain.The third chapter describes E-field-controlled magnetization in CoFeB/(001)-miscut PMN-PT magnetoelectric heterostructure.Firstly,we summarize the research development and limitation of CoFeB/PMN-PT magnetoelectric heterostructure.Next,we measure the anisotropic magnetoresistance using an in-situ home-made device and the results indicate non-volatile 35° magnetic easy axis(MEA)rotation can be achieved with the E-field reversal.More,the in-plane strain rotation can be interpreted as the driving force to rotate the MEA synchronously.This result prove that miscutted PMN-PT is more suitable to serve as the ferroelectric substrate in magnetoelectric hetero structure for achieving the E-field-controlled magnetization,which is crucial for the realization of electric-write and magnetic-read random access memeory.The last chapter makes a conclusion and elaborates the usefulness and innovativeness of our work.It also provides advice for future design.By further optimizing the PMN-PT miscut process,we could obtain the desirable polarization switching pattern under applied external E-field.Therefore,more suitable in-plane strain will be produced to modulate the magnetization. |
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