Microstructural and domain effects in epitaxial CoFe2O4 films on MgO with perpendicular magnetic anisotropy

Comès, R.; Gu, Man; Khokhlov, M. Z.; Lu, Jiwei; Wolf, Stuart A.

doi:10.1016/j.jmmm.2011.08.033

Cited by 23 publications

(7 citation statements)

References 22 publications

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“…22 A 12-nm CFO film was then deposited on the substrate using pulsed electron deposition (PED). 23, 24 The CFO film grows via the Volmer-Weber epitaxial growth mode, producing epitaxial islands on the surface. 25 An atomic force microscopy (AFM) surface topography scan after the growth is shown in Fig.…”

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confidence: 99%

Directed Self-Assembly of Epitaxial CoFe₂O₄–BiFeO₃ Multiferroic Nanocomposites

Comès¹,

Liu²,

et al. 2012

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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 ...

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confidence: 99%

Directed Self-Assembly of Epitaxial CoFe₂O₄–BiFeO₃ Multiferroic Nanocomposites

Comès¹,

Liu²,

et al. 2012

Self Cite

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“…The large K 1 arises from a spinorbit stabilized doublet ground state of the d 7 electronic configuration of the Co 2þ cations, which is caused by a trigonal crystal field of the Co 2þ cations (Dionne, 2009;Slonczewski, 1958a,b;Tachiki, 1960) and has resulted in CoFe 2 O 4 being included in a number of strain-driven multiferroic devices (Park et al, 2010;Zavaliche et al, 2005;Zhang, Deng, Ma, Lin, & Nan, 2008;Zheng et al, 2004). Coherently strained thin films have an out-of-plane easy axis, as predicted by their large, positive K 1 constant (Chambers et al, 2002;Comes, Gu, Khokhlov, Lu, & Wolf, 2012;Dhakal et al, 2010;Dorsey, Lubitz, Chrisey, & Horwitz, 1996;Lisfi et al, 2007;. Coherently strained thin films have an out-of-plane easy axis, as predicted by their large, positive K 1 constant (Chambers et al, 2002;Comes, Gu, Khokhlov, Lu, & Wolf, 2012;Dhakal et al, 2010;Dorsey, Lubitz, Chrisey, & Horwitz, 1996;Lisfi et al, 2007;.…”

Section: Magnetic Anisotropy Of Cofe 2 Omentioning

confidence: 91%

Epitaxial growth of magnetic-oxide thin films

Moyer

Mangalam

Martin

2015

Epitaxial Growth of Complex Metal Oxides

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Complex oxides represent a vast class of materials encompassing a wide range of crystal structures and functionalities. Amongst these interesting properties, the study of ferroic order (namely ferromagnetic, ferroelectric, ferroelastic, and multiferroic properties) has driven considerable research over the past few decades. Driven by the development of new synthesis techniques-especially for thin films-the field of functional oxide materials has experienced unprecedented growth in terms of the discovery of new materials systems, characterization and understanding of the fundamental properties and nature of existing systems, and in the control of properties in these materials through elegant changes in crystal chemistry (i.e., doping), strain, and other variables. Throughout this book, many examples of how these aspects can be applied to complex-oxide materials have been developed. In this chapter, in turn, we focus on advances in the growth and characterization of magnetic oxide materials while investigating the structure, properties, and synthesis of modern magnetic complex-oxide thin films. We will investigate a number of prototypical examples of materials within this subgroup of ferroic oxides and will delve into the coupling of epitaxial constraint and magnetic properties and how this diverges from bulk materials. Magnetism and major magnetic-oxide systems Magnetism in oxidesMagnetic materials violate time-reversal symmetry, but are invariant under spatial inversion; in other words, when magnetic moments are present in a crystal, the antisymmetry operator must also be present. The 32 classical crystallographic point groups do not have the antisymmetry operator and hence cannot fully describe the symmetry of magnetic crystals. Symmetry analysis reveals 122 total magnetic space groups of which only 31 can support ferromagnetism (Aizu, 1970;Laughlin, Willard, & McHenry, 2000). A material is said to be a ferromagnet when there is long-range, parallel alignment of the atomic moments resulting in a spontaneous net magnetization even in the absence of an external field. Ferromagnetic materials undergo a phase transition from a high-temperature phase that does not have macroscopic magnetization Epitaxial Growth of Complex Metal Oxides. http://dx.

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“…Additionally, the presence of dislocations or antiphase boundaries in CFO has been shown to reduce the saturation magnetization of the material and reduce the energy barrier to form magnetic domain walls. [31][32][33] Thus, the structural defects that are present in this pillar could negatively affect the performance of the CFO-BFO nanocomposite in a memory or logic device. Further studies are needed to determine the best means to produce uniform microstructure in pillars over a large pattern area.…”

Section: Microstructural Effectsmentioning

confidence: 99%

Microstructural effects of chemical island templating in patterned matrix-pillar oxide nanocomposites

Comès

Siebein

et al. 2015

CrystEngComm

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The ability to pattern the location of pillars in epitaxial matrix -pillar nanocomposites is a key challenge to develop future technologies using these intriguing materials. One such model system employs a ferrimagnetic CoFe2O4 (CFO) pillar embedded in a ferroelectric BiFeO3 (BFO) matrix, which has been proposed as a possible memory or logic system. These composites self-assemble spontaneousl y with pillars forming through nucleation at a random location when grown via physical vapor deposition. Recent results have shown that if an island of the pillar material is pre-patterned on the substrate, it is possible to control the nucleation process and determine the locations where pillars form. In this work, we employ electron microscopy and xray diffraction to examine the chemical composition and microstructure of patterned CFO -BFO nanocomposites. Cross-sectional transmission electron microscopy is used to examine the nucleation effects at the interface between the template island and resulting pillar. Evidence of grain boundaries and lattice tilting in the templated pillars is also presented and attributed to the microstructure of the seed island.

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Microstructural and domain effects in epitaxial CoFe2O4 films on MgO with perpendicular magnetic anisotropy

Cited by 23 publications

References 22 publications

Directed Self-Assembly of Epitaxial CoFe₂O₄–BiFeO₃ Multiferroic Nanocomposites

Directed Self-Assembly of Epitaxial CoFe₂O₄–BiFeO₃ Multiferroic Nanocomposites

Epitaxial growth of magnetic-oxide thin films

Microstructural effects of chemical island templating in patterned matrix-pillar oxide nanocomposites

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Microstructural and domain effects in epitaxial CoFe2O4 films on MgO with perpendicular magnetic anisotropy

Cited by 23 publications

References 22 publications

Directed Self-Assembly of Epitaxial CoFe2O4–BiFeO3 Multiferroic Nanocomposites

Directed Self-Assembly of Epitaxial CoFe2O4–BiFeO3 Multiferroic Nanocomposites

Epitaxial growth of magnetic-oxide thin films

Microstructural effects of chemical island templating in patterned matrix-pillar oxide nanocomposites

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Directed Self-Assembly of Epitaxial CoFe₂O₄–BiFeO₃ Multiferroic Nanocomposites

Directed Self-Assembly of Epitaxial CoFe₂O₄–BiFeO₃ Multiferroic Nanocomposites