Perpendicular Magnetic Tunnel Junctions with Unconventional Tunneling Barriers

Abstract

Spintronics has become an area of interest for future computing beyond the transistor. Of particular interest is the storage of data in magnetic states with the use of Magnetic Tunneling Junctions (MTJs). An MTJ consists of two ferromagnetic layers seperated by a thin insulating barrier, the standard stucture being CoFeB/MgO/CoFeB. One focus of current spintronics research is lowering the switching energy of nanomagnets in MTJs. A nanomagnet can be switched by a magnetic field governed by Ampere’s law, or by current-induced spin transfer torques and spin-orbit torques. For future spintronic applications, it is highly desirable to accomplish magnetization switching with voltage, which, by eliminating Joule heating, could dramatically reduce the switching energy. In this work two new MTJ barrier materials are investigates with a focus on the unique voltage controllable magnetic properties they bring to MTJs with perpendicular magnetic anisotropy (pMTJs). For the first-time voltage controllable interlayer coupling (VCIC) has been experimentally demonstrated with the use of a GdOX tunneling barrier. Due to the interfacial nature of the magnetism, the ability to move oxygen vacancies within the barrier, and a large proximity-induced magnetization of GdOx, both the magnitude and the sign of the interlayer coupling in these junctions can be directly controlled by voltage. In the final portion of this dissertation pMTJs with an antiferromagnetic CrOx tunneling barrier are explored. Due to the unique properties of CrOX the direction of the exchange bias between it and the bottom CoFeB FM layer can be changed thus modifying the hysteretic properties of the MTJ.