Local structure in CoFe/Al 2O 3 multilayers determined by nuclear magnetic resonance

Abstract

We studied NMR spectra at 1.5 K in a series of [Co 80Fe 20( t)/Al 2O 3(3 nm)] 10 multilayers. The spectra are interpreted by mixed contributions from Co atoms inside CoFe granules and at their interface with Al 2O 3. They display three characteristic shapes when t varies from 0.8 to 2 nm. These shapes have been interpreted as resulting from granular CoFe layers for the thinnest ones ( t<1.3 nm), and continuous CoFe layers for the thickest ones ( t>1.6 nm), with an intermediate regime—pancake grains of different sizes—in between. These structural data correlate with three magnetic states deduced from the FMR and SQUID measurements in this system.