Oscillatory interlayer exchange coupling in[Pt∕Co]n∕NiO∕[Co∕Pt]nmultilayers with perpendicular anisotropy: Dependence onNiOandPtlayer thicknesses

Abstract

Interlayer exchange coupling has been studied in a series of ${[\mathrm{Pt}({t}_{\mathrm{Pt}}\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}})∕\mathrm{Co}(4\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}})]}_{n}∕\mathrm{NiO}({t}_{\mathrm{NiO}})∕{[\mathrm{Co}(4\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}})∕\mathrm{Pt}({t}_{\mathrm{Pt}}\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}})]}_{n}$ multilayers with perpendicular anisotropy. The coupling oscillates between antiferromagnetic and ferromagnetic as a function of ${t}_{\mathrm{NiO}}$ with a period of $\ensuremath{\sim}5\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$, and the oscillatory behavior is related to the antiferromagnetic ordering of the $\mathrm{NiO}$ layer. This interlayer coupling between two $\mathrm{Co}∕\mathrm{Pt}$ multilayers is shown to occur domain by domain by magnetic force microscopy imaging. For the strongest antiferromagnetic coupling at ${t}_{\mathrm{NiO}}=11\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$, an oscillation with a period of $\ensuremath{\sim}6\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$ is superposed onto the exponential decay of the coupling strength as a function of ${t}_{\mathrm{Pt}}$. The exponential decay with ${t}_{\mathrm{Pt}}$ is ascribed to the exponential decay of the coupling between the $\mathrm{Co}$ layers across the $\mathrm{Pt}$ layers in each $\mathrm{Co}∕\mathrm{Pt}$ multilayer, and the superposed oscillatory behavior can be attributed to multiple reflections of electron waves at the $\mathrm{Co}∕\mathrm{Pt}$ interfaces and their interference. A linear dependence of the antiferromagnetic coupling strength on $1∕n$, (where $n$ is the number of repeats), is suggestive of a surface interaction for this interlayer coupling.