Thickness-dependent Curie temperature in ferrimagnetic Gd–Co/Ti multilayers

• Gd–Co/Ti multilayers were prepared by magnetron sputtering.
• The Curie temperature variation was studied as a function of the Gd–Co layer thickness.
• Finite-size effect seems to be responsible for the Gd–Co “effective” composition change.

Gd–Co/Ti multilayers were prepared by magnetron sputtering deposition onto glass substrates. It was found, that the amount of cobalt determined by energy dispersive X-ray spectroscopy (EDX) analysis decreased from 77.9 down to 74.4 at% with a decrease of the GdCo layer thickness from 250 nm to 3 nm. For relatively thick layers this compositional change correlates well with the observed changes in the compensation temperature. However, for thinner Gd–Co layers the Curie temperatures (TC) taken in conjunction with the composition dependence of TC would require a significant change in composition much more important than the one observed by EDX. The reason for this discrepancy between the results of EDX analysis and the “effective” composition obtained by means of magnetic analysis is the sharp decrease in TC as a result of finite size effect.