Electric Field Control Of Magnetism In Ferromagnetic/Ferroelectric Heterostructures

With the development of information technology towards high density and low energy consumption, the requirement of storage technology is higher and higher. In the insight of improving density, the “electric write/ magnetic read” concept of multistate storage is presented. Compared with current, the way of electric field control of magnetism is low power consumption, high efficiency and convenient manner. The electric field control of magnetism usually exists in artificial ferromagnetic（FM）/ferroelectric（FE） heterostructures. The magnetoelectric coupling process can be classified according to its origin in strain-mediated and charge-mediated mechanisms. The problem of strain-mediated mechanisms is how to realize non-volatile tuning, and the charge-mediated mechanism exists rich physics phenomena. Therefore, we fabricated FeCo doped NiFe₂O₄（FeCo-NFO） and single-crystalline Fe films, which depositing on top of Pb(Mg_1/3Nb_2/3)_0.7Ti_0.3O₃（PMN-PT） by using magnetron sputtering and molecular beam epitaxy respectively, and the electric field control of magnetism of these two heterostructures was investigated by vibrating sample magnetometer, ferromagnetic resonance, and the transport properties test system which was constructed by ourselves. The main results are as follows:1. By using magnetron sputtering method, the Fe Co-NFO films was deposited on（011）-oriented single-crystalline PMN-PT substrate, and then the electric field control of magnetic transport properties of FeCo/PMN-PT heterostructures was investigated. The non-volatile tri-state storage was realized at room temperature by pulse electric field. Compared with magnetoresistance and magnetization test, the resistance of FeCo-NFO/PMN-PT heterostructures is dependent greatly on the ferroelectric layer’s ferroelectricity and the ferromagnetic layer’s magnetization.2. By using molecular beam epitaxy method, the different thickness single-crystalline Fe films was deposited on（011）-oriented single-crystalline PMN-PT substrate, and the electric field control of static magnetic studies on single-crystalline Fe/PMN-PT heterostructures found that the remnant magnetization of single-crystalline Fe/PMN-PT heterostructures exhibits asymmetric loop-like response to electric field. The surface anisotropy constant of single-crystalline Fe with different thickness and under different electric field were quantitative analysed, which illustrates that the main magnetoelectric coupling mechanism of single-crystalline Fe/PMN-PT heterostructures is charge mediated mechanism.3. The dynamic magnetic studies on ferromagnetic resonance of single-crystalline Fe/PMN-PT explains that the electric field changes the resonance field, and the symmetric of curves is also loop-like which is similar to the phenomenon in static magnetic studies. What is worth mentioning is the changes of ferromagnetic resonance shape, especially the fully flip under large electric field, which further more illustrates the charge-mediated mechanism. According to the liner magnetoelectric coupling method, the polarization and magnetization coupling results in spin-driven screening effect which tunes the magnetization precession process under microwave irradiation.