Thermal constraints and the quantum limit will soon put a boundary on the scale of new micro and nano magnetoelectronic devices. This necessitates a push into the limits of harnessable natural phenomena to facilitate a post-Moore’s era of design. Requirements for thermodynamic stability at room temperature, fast (Ghz) switching, and low energy cost narrow the list of candidates. Molecular electronic frontier orbital structure of some d-block transition metal ions in crystal fields will deform in response to their local energetic environment, giving rise to the eg and t2g suborbitals. More specifically, in an mononuclear Fe(II) complex, the energetic scale between these two orbitals yields an S=0 low spin diamagnetic state and an S=2 high spin paramagnetic state. Spin crossover complex [Fe{H2B (pz) 2 }2 (bipy)] will show locking of its spin state well above the transition temperature, with an accompanied change of conductivity, when placed in a polar environment. Here we show voltage controllable, room temperature, stable locking of the spin state, and the corresponding conductivity change, when molecular thin films of [Fe{H2B (pz) 2 }2 (bipy)] are deposited on a ferroelectric polyvinylidene fluoride hexafluropropylene substrate. This opens the door to the creation of a thermodynamically stable, room temperature, molecular multiferroic gated voltage device.

<p dir="ltr">Multiferroics, which exhibit multiple ferroic orderings within a single material system, have substantial potential for applications in sensors, transducers, memory devices, and energy harvesters. However, the development of single-phase multiferroics that demonstrate roomtemperature properties remains limited by inherent contradictions in d-orbital occupancy between magnetic and ferroelectric materials. This dissertation focuses on addressing this challenge through the exploration of a novel bismuth-based, single-phase multiferroic thin film that features an exotic layered supercell (LSC) structure and displays multiferroic properties at room temperature. The primary aim is to deepen the understanding of LSC materials and advance their applications in practical devices. The dissertation is structured as follows: It begins with an introduction to the fundamental concepts of multiferroics, including their classifications and applications, the specific characteristics and growth mechanism of LSC materials, and other relevant background knowledge. This is followed by a detailed description of the experimental techniques employed. The core of this dissertation comprises four chapters that present a comprehensive study of LSC materials. The first chapter discusses a nanocomposite system combining an LSC material, Bi1.25AlMnO3.25, with Au nanoparticles (NPs), highlighting its tunable microstructure and multifunctional properties influenced by growth temperature. The second chapter explores the integration of Bi2NiMnO6 on a flexible mica substrate, demonstrating the potential of LSC materials for use in flexible electronics, with performance maintained across various bending conditions. The third chapter details the development of freestanding LSC thin films by utilizing a water-soluble sacrificial layer, which are shown to preserve their microstructure and properties after being transferred onto a silicon substrate. Building on this, the fourth chapter investigates the reuse of recycled SrTiO3 substrates for subsequent thin film growth, examining changes in surface strain states and chemistry to guide sustainable practices in complex oxide thin film processing. In summary, this dissertation presents an extensive examination of LSC multiferroics, revealing their significant promise for multifunctional applications and integration into flexible and silicon-based electronics. Additionally, the work explores sustainable methods for substrate reuse, contributing further to the field of material sciences.<br></p>