Nanocolumnar Interfaces and Enhanced Magnetic Coercivity in Preferentially oriented Cobalt Ferrite Thin Films Grown Using Oblique-Angle Pulsed Laser Deposition

Abstract

Highly textured cobalt ferrite (CFO) thin films were grown on Si (100) substrates using oblique-angle pulsed laser deposition (α-PLD). X-ray diffraction and in-depth strain analysis showed that the obliquely deposited CFO films had both enhanced orientation in the (111) crystal direction as well as tunable compressive strains as a function of the film thicknesses, in contrast to the almost strain-free polycrystalline CFO films grown using normal-incidence PLD under the same conditions. Using in situ optical plume diagnostics the growth parameters in the α-PLD process were optimized to achieve smoother film surfaces with roughness values as low as 1-2 nm as compared to the typical values of 10-12 nm in the normal-incidence PLD grown films. Cross-sectional high resolution transmission electron microscope images revealed nanocolumnar growth of single-crystals of CFO along the (111) crystallographic plane at the film-substrate interface. Magnetic measurements showed larger coercive fields (∼10 times) with similar saturation magnetization in the α-PLD-grown CFO thin films as compared to those deposited using normal-incidence PLD. Such significantly enhanced magnetic coercivity observed in CFO thin films make them ideally suited for magnetic data storage applications. A growth mechanism based on the atomic shadowing effect and strain compression-relaxation mechanism was proposed for the obliquely grown CFO thin films.

Perspectives on oblique angle deposition of thin films: From fundamentals to devices

“…Remarkably, a key feature in this technique is the conservation of the target stoichiometry when employing multicomponent targets. Moreover, in general conditions, the highly energetic character of the species in the plume promotes that thin films usually grow compact, although nanocolumnar and porous thin films can be grown by intentionally introducing typical OAD geometries [173][174][175][176][177][178]. Much like the OAD of thin films prepared by evaporation or MS, the main purpose in most cases is the effective control of texture alignment so as to obtain a columnar microstructure and/or porous layers.…”

“…Much like the OAD of thin films prepared by evaporation or MS, the main purpose in most cases is the effective control of texture alignment so as to obtain a columnar microstructure and/or porous layers. For example, in cobalt ferrite oxide thin films, preferential orientation along the [1 1 1] crystal direction and compressive strain tunable as a function of film thickness can be obtained by PL-OAD, whereas almost strain-free and random polycrystalline layers are produced when using normal-incidence PLD under the same conditions [177]. Nanocolumnar mixed oxide thin films, including YBa 2 Cu 3 O x [179] and La 0.7 Sr 0.3 MnO 3 [180], have been prepared by PL-OAD to take advantage of the preservation of the target stoichiometry.…”

Enhanced Magnetism in Highly Ordered Magnetite Nanoparticle‐Filled Nanohole Arrays

“…This can be attributed to the competition between the demagnetization energy of quasi‐1D nanostructure and the magnetocrystalline anisotropy energy of nanoparticles in nanoholes. A similar phenomenon has also been reported for La 0.7 Sr 0.3 MnO 3 films composed of magnetic nanocolumnar structures …”

Multiferroic vertically aligned nanocomposite with CoFe2O4 nanocones embedded in layered Bi2WO6 matrix

“…On the other hand, CoFe 2 O 4 (CFO) with a spinel structure (Figure 1(a)) is an important ferromagnetic material with excellent magnetic property such as high coercivity, moderate saturation magnetization, as well as high chemical and structural phase stability [18,19]. Furthermore, because of the high magnetostriction coefficient, it shows the possibility of tuning magnetization by lattice strain [20].…”