Self-assembled vertically aligned oxide nanocomposites consisting of magnetic pillars embedded in a ferroelectric matrix have been proposed for logic devices made from arrays of magnetostatically interacting pillars. To control the ratio between the nearest neighbor interaction field and the switching field of the pillars, the pillar composition CoxNi1-xFe2O4 was varied over the range 0 ≤ x ≤ 1, which alters the magnetoelastic and magnetocrystalline anisotropy and the saturation magnetization. Nanocomposites were templated into square arrays of pillars in which the formation of a "checkerboard" ground state after ac-demagnetization indicated dominant magnetostatic interactions. The effect of switching field distribution in disrupting the antiparallel nearest neighbor configuration was analyzed using an Ising model and compared with experimental results.
grow as a tetragonal structure with a large c/a ratio (≈1.25) when the compressive epitaxial strain exceeds ≈4.5%, e.g., when grown on LaAlO 3 (LAO). [29] In previous work on BFO-CFO nanocomposites, (001)-oriented pseudocubic substrates were typically used, and there is little work on nanocomposites grown with (110) and (111) orientations. [21,31,32] The CFO nanopillars in nanocomposites grown on (110) and (111) substrates appear as tent-like structures and triangular prisms, respectively, in contrast to the rectangular pillars obtained on the (001)-oriented substrates. Moreover, BFO films grown on (110)-oriented LAO exhibit a uniaxial in-plane strain instead of the biaxial strain found in the (001) orientation, [33,34] and the strain along the [110] in-plane direction is relaxed even in BFO films with a thickness as low as ≈10 nm. BFO-CFO nanocomposite films on (110)-oriented LAO also exhibit strain in the out-of-plane direction of both phases that differs from the strain state obtained in single-phase films. A large out-of-plane strain significantly modifies the magnetism, magnetic anisotropy, and magnetotransport properties in vertical nanocomposite films. [10] In this article, we show that the BFO in a BFO-CFO nanocomposite grown on LAO (110) substrates forms different phases, rhombohedral-like (R-like) or tetragonal-like (T-like), depending on the thickness of the film and the effects of the vertical lattice strain between the BFO and CFO. A variety of domain structures were observed in the BFO matrix, and thickness-dependent magnetic properties of the CFO are interpreted in terms of the film strain and the shape of the CFO. These results demonstrate how the properties of nanocomposites including in-plane anisotropy can be engineered on a (110) substrate.
Results and DiscussionA series of epitaxial BFO-CFO nanocomposite thin films with thickness of 25 to 75 nm was deposited on single-crystal LAO (110). The LAO is a rhombohedrally distorted perovskite at room temperature, with a pseudocubic lattice parameter of 3.787 Å. The (110)-oriented LAO substrate therefore has a rectangular surface net with dimensions 5.355 Å along the pseudocubic [110] sub direction and 3.787 Å along the [001] sub direction. The films were grown using pulsed laser deposition (PLD) as described in the Experimental Section. A conductive La(Sr 0.33 ,Mn 0.67 )O 3 (LSMO) layer ≈8 nm thick was first epitaxially grown on the substrate, followed by deposition of the A strain-driven BiFeO 3 (BFO) tetragonal to rhombohedral phase transition is demonstrated in self-assembled BiFeO 3 -CoFe 2 O 4 (BFO-CFO) nanocomposites on LaAlO 3 (110)-oriented substrates with varying thickness. The CFO forms parallel nanoscale fin-shaped structures within a BFO matrix. Out-of-plane lattice strain from the BFO/CFO interfaces stabilizes the BFO rhombohedrallike phase. The BFO exhibits a range of ferroelectric textures including stripe domains and centered domain arrangements, and the magnetic anisotropy of CFO shows a thickness-dependent reorientation.
Sputter-grown self-assembled epitaxial spinel–perovskite nanocomposites consisting of CoFe2O4 pillars in a BiFeO3 matrix on Nb-doped SrTiO3 or SrTiO3-buffered Si substrates.
In article number 1900012, Guo Tian and co‐workers show a tetragonal‐like to rhombohedral‐like phase transition in magnetoelectric nanocomposites. They explore various ferroelectric textures of BiFeO3, including stripe domains and centered domain arrangements and the magnetic anisotropy of CoFe2O4. These composites offer the opportunity to study nanoscale ferroelectric textures and may ultimately be useful in magnetoelectric devices.
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