Modulated magnetization depth profile in dipolarly coupled magnetic multilayers

Abstract

Polarized neutron reflectivity (PNR) and magnetometry studies have been performed on the metal-insulator multilayer ${[{\mathrm{Co}}_{80}{\mathrm{Fe}}_{20}(1.6\phantom{\rule{0.3em}{0ex}}\mathrm{nm})∕{\mathrm{Al}}_{2}{\mathrm{O}}_{3}(3\phantom{\rule{0.3em}{0ex}}\mathrm{nm})]}_{9}$ which exhibits dominant dipolar coupling between the ferromagnetic layers. Our PNR measurements at the coercive field reveal a novel and unexpected magnetization state of the sample, exhibiting an oscillating magnetization depth profile from CoFe layer to CoFe layer with a period of five bilayers along the multilayer stack. With the help of micromagnetic simulations we demonstrate that competition between long- and short-ranged dipolar interactions apparently gives rise to this unprecedented phenomenon.