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 ...

Many works have demonstrated perpendicular magnetic anisotropy in CoFe2O4-BiFeO3 (CFO-BFO) composites, which is commonly believed to originate from out-of-plane compressive strain in the CFO pillars due to the lattice mismatch with the BFO matrix. Others have shown that the pillar−matrix interface in similar NiFe2O4-BFO composites is fully relaxed. To study the origin of the magnetic anisotropy, composite films were grown on SrTiO3 with thicknesses ranging from 13 to 150 nm via pulsed electron deposition. In-plane compressive strain in the pillars is found for thinner samples, which induces in-plane magnetoelastic anisotropy. A model for the origin of this previously unreported strain is proposed and the results are contrasted with the thicker composite films found in the literature.

Complex oxide epitaxial film growth is a rich and exciting field, owing to the wide variety of physical properties present in oxides. These properties include ferroelectricity, ferromagnetism, spin-polarization, and a variety of other correlated phenomena. Traditionally, high quality epitaxial oxide films have been grown via oxide molecular beam epitaxy or pulsed laser deposition. Here, we present the growth of high quality epitaxial films using an alternative approach, the pulsed electron-beam deposition technique. We demonstrate all three epitaxial growth modes in different oxide systems: Frank-van der Merwe (layer-by-layer); Stranski-Krastanov (layer-then-island); and Volmer-Weber (island). Analysis of film quality and morphology is presented and techniques to optimize the morphology of films are discussed.

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