Electric-field Control Of Magnetism And Tunnel Magnetoresistance In Multiferroic Heterostructures

Recently, the new concepts of multifunctional magnetoelectric devicesbased on multiferroic materials, are considered as powerful contenders in thenext generation microwave electronics and spintronic devices. Due to its simplestructure and giant electric-field effect, stress-mediated coupling system isconsidered to be more possible to achieve application in the short term.However, there are still existing some key issues in stress-mediated couplingsystems. For example, how the ferroelectric domain and its switching influencethe electric-field-controlled magnetism bevaviors at micro scale are not so clear,which are not only important for scientific significance, but also important forthe high density devices application. Secondly, although it has been presented torealize the electric-field modulating spintronics devices through thestress-mediated coupling, however the experiment about electric field control ofthe MTJs without the assistance of magnetic field is still lacking. In this context,we have investigated the electric-field-controlled magnetism and tunnelmagnetoresistance based on CoFeB/PMN-PT multiferroic heterostructure. Thework is divided into two parts as follows:CoFeB/PMN-PT(001) heterostructures with abundant FE domain structuresand without magnetocrystalline anisotropy were fabricated using a magnetronsputtering system. To investigate electric-field control of magnetism at microscale, Scan Kerr Microscopy (SKM) with the in situ electric fields were used.Combining the macro-magnetic properties measured by SQUID with in situelectric field, we found spatial resolution of two types of magnetizationresponse to extarnal electric fields in CoFeB/PMN-PT(001) system: Loop-likeand Butterfly-like behaviors, respectively. Moreover, through the angledependence of the electric field control of magnetism behaviors and FEdomain-switching analysis, we proposed that different types of FEdomain-switching of PMN-PT resulting in the spatial distribution ofelectric-field control of magnetism behaviors. And temperature dependence ofelectric filed control of magnetism and micromagnetic simulation were preformed to support our discussion. These investigations are useful for furtherdesign of electric-field-control magnetism through domain engineering, which issignificant for future application.In another aspect, magnetic multilayer structure MTJs were fabricated onthe top of PMN-PT(011) substrates using a magnetron sputtering system.Through multipe in situ electric field technologys, we found a continuousmagnetization rotation of FL and PL tuned by applied fields. Based on this, wefurther fabricated the AlOx-MTJs/Piezeoelctrics devices, and firstlydemonstraing a manipulation of TMR at room temperature in MTJ/piezoelectricstructure by electric fields without the assistance of a magnetic field, which isimportant for the electric-field controlled spintronic devices.