Interface driven functionality in
nanolayered materials
Interface
effect on magnetic properties of Cu/Au/Co/Au multilayers
Methods of tailoring magnetic anisotropy of ultra thin films have potential applications as high density information storage device or sensors. Preliminary studies have shown that one can vary magnetic anisotropy of thin Co films by changing the thickness of Au under layer.
Cu/Au/Co/Au nanolayer thin films have
been grown epitaxially on Si substrates using molecular beam epitaxy (MBE)
technique. Two sets of nanolayers were grown using this technique. The only
difference between the two sets is the thickness of Au under layer is either 2
monolayer (ML) or 6 ML.
|
A schematic of stacking sequence in Cu/Au/Co/Au
nanolayers prepared by molecular beam epitaxy technique. |
High resolution TEM studies have shown that the crystal structure
of Co is different in the two cases. Co has fcc crystal structure in the case
of 2ML Au, whereas it has hexagonal closely packed (hcp) structure in the case
of 6ML Au. It is unexpected to have a different Co crystal structure simply by
varying the Au underlayer thickness.
Co has metastable fcc crystal structure in the case of 2 ML Au. Co has stable hcp crystal structure in the case of 6 ML Au.
Interestingly specimen with 2ML Au shows in-plane magnetic
anisotropy, whereas the other one, with 6ML Au shows out-of-plane magnetic anisotropy.
The variation of magnetic properties with different Au underlayer thickness
could be correlated with different Co crystal structures and strains associated
with lattice mismatch.
Co has in-plane magnetic anisotropy in the case of 2 ML Au.
Co has out-of-plane magnetic anisotropy in the case of 6 ML Au.
To unravel fundamental mechanisms of strain induced variation of
magnetic anisotropy, we are investigating the microstructural details using synchrotron
beams and performing theoretical studies using molecular dynamics simulations
and ab initio calculations.
In collaboration with Los Alamos National Laboratory
References:
“Tunable magnetic anisotropy of ultrathin Co layers”, S. Park, X. Zhang, A. Misra, J. D. Thompson, M. R. Fitzsimmons, S. Lee, and C. M. Falco, Appl. Phys. Lett., 86, (2005) 042504. (PDF)