Exchange coupling in Co-Ti layered structures

The Co-Ti multilayers with constant thickness sublayers and Co-d(Ti)-Ti-Co trilayers with wedge-shaped Ti interlayers were prepared using an ultra hig h vacuum (5 x 10(-10) mbar) DC-RF magnetron sputtering. The planar growth o f the Co and Ti sublayers was confirmed in situ by X-ray photoelectron spec troscopy. The Co sublayers grow in the soft magnetic nanocrystalline phase (with average grain size D << 10 nn) up to a critical thickness d(crit) sim ilar to 3 nm. For a thickness greater than d(crit), the Co sublayers underg o a structural transition to the polycrystalline phase with D > 10 nm. Resu lts show that the Co sublayers are very weakly exchange coupled or decouple d for d(Ti) > 2.7 nn. The rapid decrease of the interlayer exchange couplin g could be explained by its strong damping due to the formation of a non-ma gnetic quasi-amorphous Co-Ti alloy layer at the interfaces. The nanocrystal line Co sublayers with d(Co) = 2.2 nm showed a weak 90 degrees coupling nea r the transition zone (d(Ti) similar to 2 nm) from ferromagnetic to week an tiferromagnetic coupling. (C) 1999 Elsevier Science Ltd. All rights reserve d.