ELECTRIC FIELD CONTROL OF MAGNETIC PROPERTIES IN Fe/BaTiO3 MULTIFERROIC HETEROSTRUCTURES

Abstract

In traditional spintronics devices, magnetization can be controlled by injecting a current from applying a magnetic field. However, these methods have the drawback of high energy consumption. Recently, spin-transfer torque devices have emerged, eliminating the need for an external field. Nonetheless, the energy consumption remains due to increased Joule heating resulting from direct electric current writing. To address these challenges, there is a growing interest in alternative approaches that enable the processing and writing of magnetic information using electric field, thus eliminating the need for electric currents. Multiferroics (MFs), which combine both ferromagnetic (FM) and ferroelectric (FE) properties, have shown promise for electric field control of the magnetism. Among various FM/FE multiferroic heterostructures, Fe/BaTiO3 (BTO) is particularly noteworthy due to its unique intimate lattice mismatch of approximately 1.3% and high Curie temperature of Fe (780℃). BTO is a well-studied ferroelectric material with successive structural phase transitions and remarkable domain configuration at room temperature. Several reports have observed the control of magnetic anisotropy, magnetic moment, and magnetic domains of Fe film using electric field. Especially, a novel physical mechanism has been revealed, illustrating interfacial magnetoelastic coupling at the Fe/BTO interface. This discovery showcases the potential for room temperature electrical and reversible on/off switching of the interfacial magnetization, suggesting significant application in the electric field control of magnetic properties through the magnetoelectric coupling. However, experimental results with Fe/BTO films demonstrated a less-than-90o rotation of magnetization, which does not meet requirement of spintronic device basing on 180o deterministic control of magnetization. Therefore, enhancing magnetoelectric coupling is imperative. A critical condition for achieving substantial magnetoelectric coupling is a strong elastic coupling between magnetic and ferroelectric phases. To meet this requirement, epitaxial ferroelectric-ferromagnetic structures are fabricated to establish a structurally coherent interface under epitaxial strain, thus optimizing the elastic coupling between FM and FE phase. This dissertation primarily focus on enhancing the quality of Fe films by adjusting the growth temperature and controlling the magnetism and magnetic domains within these films thorough the application of external electric field. Furthermore, this provides valuable insights into the evolution of BTO domain configurations during the application of electric fields, revealing the formation of a single in-plane domain under the influence of an out- of-plane electric field.