1. Department of Materials Science and EngineeringCollege of EngineeringPeking University Beijing 100871 China
2. Electronic Materials Research LaboratoryKey Laboratory of the Ministry of Education and International Center for Dielectric ResearchSchool of Electronic and Information EngineeringXi'an Jiaotong University Xi'an 710049 China
3. Beijing Key Laboratory for Magnetoelectric Materials and DevicesPeking University Beijing 100871 China