Templated Multiferroic Nanocomposites by Ion-Lithography

Abstract

Vertical aligned nanocomposites (VAN), formed by phase separation of two different materials, have been a novel platform to study heteroepitaxy. The perovskite-spinel system is one of the most popular VAN structures to study multiferroic coupling. For example, ferroelectric BiFeO3 (BFO) and ferrimagnetic CoFe2O4 (CFO) could grow epitaxially on [001]-SrTiO3 substrate, forming BFO matrix and CFO pillars. In this thesis, we focus on three things:

First, the possibility of integrating perovskite on garnet Gd3Ga5O12 (GGG) substrate is explored. Perovskite candidates YFeO3 and BaTiO3 are integrated with garnet Y3Fe5O12. Growth mechanism, structure characterization and magnetic properties of as-grown films are discussed.

Second, ion-lithography enabled by the VELION FIB-SEM system is developed to template the perovskite—spinel system. Specifically, fin-shaped BFO—CFO nanocomposite is synthesized by pulsed laser deposition (PLD). Nucleation mechanism of CFO on patterned STO substrates together with atomic characterization is discussed.

Last, a customized micro-magnetics module in COMOL Multiphysics is built based on the weak formulation of Landau-Lifshitz-Gilbert (LLG) equation. Magnetic properties of single crystal CFO are modeled.