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

Mukherjee, Devajyoti, Hordagoda, Mahesh, Hyde, Robert, Bingham, Nicholas, Srikanth, Hariharan, Witanachchi, Sarath, Mukherjee, Pritish
ACS Applied Materials & Interfaces 2013 v.5 no.15 pp. 7450-7457
X-ray diffraction, cobalt, databases, diagnostic techniques, ferrimagnetic materials, roughness, silicon, transmission electron microscopes
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.