Alteration of magnetic anisotropy of Pt/Co/Pt trilayers by FIB irradiation

Investigation of the magnetic thin film structures with the out-of-plane magnetization are important for both fundamental research and applications. In nanostructures with decreasing magnetic film thickness an out-of-plane alignment of magnetization is frequently observed due to increasing contribution of surface anisotropy. It has been shown that ion beam irradiation modifies magnetic properties of such structures [1, 2]. With increasing irradiation dose D of such films the strength of perpendicular anisotropy is suppressed, magnetization rotates towards in-plane alignment or ferromagnetic ordering is converted to the superparamagnetic state. Very recently an oscillatory behaviour of magnetic anisotropy between the in-plane and out-of-plane states driven by an increasing dose of 30 keV Ga+ ion homogenous irradiation, has been observed in the molecular beam epitaxy (MBE) deposited Pt/(Co 3.3 nm)/Pt films [3].
The aim of this work is investigation of local modifications of magnetic properties in MBE grown Mo/Pt(20nm)/(Co3.3nm)/Pt(5nm) films by a focused ion beam (FIB). In the studied as deposited structure magnetization was aligned in the film plane. Numerous spots of the sample (squares 100x100μm² or 50x50μm²) have been locally irradiated with Ga+ ions with energy of 30 keV and different doses D ranging between 2•10^12 and 1•10^16 ions/cm². FIB irradiated spots were probed using polar/longitudinal Kerr effect magnetometry (sensitive to perpendicular/longitudinal magnetization component) and atomic/magnetic force microscopy techniques. Creation of the two out-of-plane magnetization branches upon increasing FIB irradiation dose D was observed, similarly to the effect reported for homogenous irradiation [3].
Presented results seem to be promising for new method for magnetic nanostructure patterning.

[1] C. Chappert et al., Science 280, 1919 (1998).
[2] J. Fassbender et al., J. Magn. Magn. Mat. 320, 579 (2008).
[3] A. Maziewski et al., Phys. Rev. B 85, 054427 (2012).