Finite-size effect in CoAlZr/AlZr multilayers

University essay from Uppsala universitet/Materialfysik

Abstract: The structural and magnetic properties of amorphous Cox(Al80Zr20)1-x multilayers with varying thicknesses of the magnetic bilayers have been investigated. The reduction of the thickness causes a reduction of the critical temperature, Tc, this is known as the finite-size effect. The multilayers were grown using DC magnetron sputtering, co-sputtering was used with cobalt and an Al80Zr20 alloy target to create an amorphous CoAlZr alloy. The total thickness of the multilayers was chosen to be held constant at 60 nm and the Al80Zr20 spacing layers were thick enough to suppress any interlayer exchange coupling effects. Estimating the composition using RBS proved difficult with great uncertainties in the measured amount of aluminium in the samples. The amorphousness of the samples was investigated using GIXRD and all measured samples display x-ray amorphousness. Fits of XRR measurements showed that the bilayers displayed a rather large roughness, the origin of this roughness is unknown. MOKE measurements showed that the CoAlZr alloys exhibit a noncollinear spin structure at magnetic bilayer thicknesses of 6 nm and below. The samples’ noncollinear spin structure lead to the loss of remanence. Attempts at measuring the critical temperature with DC measurements using the remanence at zero field were therefore unsuccessful. AC susceptibility with SQUID should allow an accurate measurement of the critical temperature.

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