Abstract
Perpendicular magnetization and precise control over the magnetic easy axis in magnetic thin film is necessary for a variety of applications, particularly in magnetic recording media. A strong (111) orientation is successfully achieved in the CoFe2O4 (CFO) thin film at relatively low substrate temperature of 100 °C, whereas the (311)-preferred randomly oriented CFO is prepared at room temperature by the DC magnetron sputtering technique. The oxygen-deficient porous CFO film after post-annealing gives rise to compressive strain perpendicular to the film surface, which induces large perpendicular coercivity. We observe the coercivity of 11.3 kOe in the 40-nm CFO thin film, which is the highest perpendicular coercivity ever achieved on an amorphous SiO2/Si substrate. The present approach can guide the systematic tuning of the magnetic easy axis and coercivity in the desired direction with respect to crystal orientation in the nanoscale regime. Importantly, this can be achieved on virtually any type of substrate.
Highlights
We demonstrate a fundamental approach for systematically modulating the maximized perpendicular magnetic anisotropy and magnetic easy axis of CFO thin film based on a consideration of the effects of crystal orientation, compressive strain anisotropy and oxygen vacancies
Our strategy is given in a scheme where the in-plane and perpendicular coercivity are associated with a crystal orientation (Fig. 1)
This approach can lead to the systematic tuning of the magnetic easy axis and coercivity, with respect to crystal orientation in a nanoscale regime; importantly, this can be achieved on any types of substrate
Summary
The sample deposited at room temperature shows that the (311) diffract line is the most intense peak, indicating the random orientation of the CFO thin film. One of the reasons for the observed strain in post-annealed CFORT(Random) film was attributed to the difference in the thermal expansion coefficient (α) between the SiO2/Si substrate (3.5 × 10−6/K) and CFO (1 × 10−5/K).
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