Directed Self-Assembly of Epitaxial CoFe₂O₄–BiFeO₃ Multiferroic Nanocomposites

Abstract

ABSTRACT. CoFe2O4 (CFO)-BiFeO3 (BFO) nanocomposites are an intriguing option for future memory and logic technologies due to the magnetoelctric properties of the system. However, these nanocomposites form with CFO pillars randomly located within a BFO matrix, making implementation in devices difficult. To overcome this, we present a technique to produce patterned nanocomposites through self-assembly. CFO islands are patterned on Nb-doped SrTiO3 to direct the self-assembly of epitaxial CFO-BFO nanocomposites, producing square arrays of CFO pillars.2 Multiferroic nanocomposite films have been heavily studied for their potential applications in magnetoelectric systems. 1 The CoFe2O4-BiFeO3 (CFO and BFO, respectively) system has generated particular interest due to the magnetoelastic properties of CFO 2 and the combination of ferroelectricity and anti-ferromagnetism in BFO 3 . It has been shown that when CFO and BFO are codeposited via physical vapor deposition at high temperatures on a SrTiO3 (001) substrate that the materials will spontaneously phase segregate to produce an epitaxial CFO pillar in an epitaxial BFO matrix, which is referred to as a 1-3 nanocomposite. 4 The CFO pillars form faceted structures with {110}-type interfaces with the BFO matrix and {111}-facets on the surface, protruding above the matrix. 5 The pattern of the CFO pillars in the structure is essentially random, since they are formed through the nucleation of a CFO island on the substrate, while BFO wets the remaining surface. Thus, to control the location of the pillars a means of controlling the nucleation site for the CFO island is needed. CFO-BFO composites have been found to demonstrate magnetoelectric coupling, allowing for electrical control of the magnetic anisotropy of the CFO pillars. 6 , 7 Based on these properties, the composite system has been proposed for both magnetoelectric memory 8 and logic 9 applications. In particular, the reconfigurable array of magnetic automata (RAMA) 9,10 is a nanomagnetic logic system based on the magnetic quantum cellular automata (MQCA) logic architecture 11 which would use a CFO-BFO 1-3 composite with the pillars arranged in a square array to create a reprogrammable logic system. However, in order to make devices using these composites, the ability to place the pillars into pre-determined arrays is required.Previous work in patterning multiferroic nanocomposites has been limited. One method to produce patterned magnetoelectric composites is to use a porous anodic aluminum oxide (AAO) film as a liftoff mask during deposition, which produces a hexagonal array pattern. 12,13 In one approach, a BaTiO3-CoFe2O4 (BTO-CFO) multilayer is deposited onto the AAO film on an STO substrate, which yields a small amount of magnetoelectric response. 12 Another technique is to use the AAO film to form CFO islands and then overcoat the islands with ferroelectric Pb(Zr,Ti)O3 (PZT), which yields a composite that is both ferroelectric and ferromagnetic. 13 Others have used a SiN membrane as a shadow mask to 3 ...

Mesocrystal-embedded functional oxide systems

“…The progress in the growth of nanostructure and nanocomposite has been a vital enabler fueling these developments. [64][65][66][67][68][69][70][71][72][73] The advancement of binary oxides has led to the flurry of modern technologies and applications. [74][75][76][77][78][79][80][81][82][83] Along with the advent of the superconductivity, CMR, and multiferroicity, complex oxides have emerged as fruitful systems to reveal the complexity induced by the interactions between charge, spin, orbital, and lattice degrees of freedom.…”

Crystalloquasichemical Model of Spinel CoFe2O4 Formation, Obtained by Chemical co-Precipitation Method

“…Будучи перспективним магнітним і електричним резистивним матеріалом, CoFe 2 O 4 знайшов широке застосування у запам'ятовуючих пристроях, магнітоелектричних перетворювачах, датчиках газу тощо [1][2][3][4][5][6][7][8]. Проте на сьогодні не описано механізм його утворення, зокрема з позицій взаємодії дефектних фаз.…”

“…Взаємодія дефектних гідроксидних кластерів з катіонними вакансіями (ІІ) та вкоріненим кобальтом (IV) матиме вигляд: 3 . Застосування квазіструктурної методики дає можливість набагато глибше пояснити механізм одержання шпінельного фериту кобальту, що можна використати під час прогнозування його властивостей, зокрема при цілеспрямованому введенні донорних та акцепторних домішок металоксидів.…”

Self-Assembled Epitaxial Multiferroic Oxide Nanostructures Grown by Pulsed Electron Deposition

“…To determine if any magnetic anisotropy was present in the films, VSM measurements were made along both the in-plane [100]-direction and the out-of-plane [001]-direction for the samples. The results of these measurements are shown in Figure 6-8(a-c).…”

“…100 In this work, the group fabricated (Fe,Zn) 3 O 4 nanoscale pads with lateral dimensions ranging from 100 nm to 3 μm and deposited a BFO film on top of the template substrate.…”