Focused ion beam induced swelling in MgO(001)

The ability to prepare ordered arrays of micro/nano sized magnetic elements off ers the chance to investigate magnetic properties at length scales previously inaccessible. Patterning of extended magnetic layers or multilayers by Focused Ion Beam (FIB) is one of the most powerful approaches for nano-structuration on a large variety of materials, due to its high spatial resolution, good process control and elevated fl exibility. MgO(001) is as a good substrate for UHV epitaxial growth of multilayers of magnetic interest, such as Fe/NiO: it is magnetically inert, it has a small lattice mismatch with respect to NiO and it is cheap and easy to prepare. In the present work we analyze ion-induced swelling effects on MgO(001) single crystals as they could infl uence the structure, morphology and, consequently, the properties of magnetic arrays prepared by FIB patterning of magnetic layers on MgO crystalline substrates. We studied by AFM the ions eff ects on the morphology of one micron size square dots array obtained on a 5–10 nm MgO/10 nm Fe/MgO(001) multilayers. A Fe interlayer has been deposited to avoid electronic charging that restricts ion beam effi ciency. 30 keV, 5x1016 Ga+cm-2 bombardment leads to a signifi cant swelling eff ect (4–6 nm protrusion) on the patterned areas. Electron diff raction and Auger depth profi le measurements suggest that the observed swelling mainly originates from MgO structural damage.