Magnetic Coupling Mediated by Magnetic Interlayers: A Polarized Neutron Reflectivity Study of Ni_.81Fe_.19/Fe Superlattices. J.F. Ankner^*, H. Kaiser^*, W. Kuch, and S.S.P. Parkin, ^*Missouri University Research Reactor, Columbia, Missouri, Max Planck Institut fr Mikrostrukturphysik, Halle, Germany, IBM Almaden Research Center, San Jose, California

The magnetic coupling of ferrous transition metals across transition-metal interlayers has been a subject of intense study over the past decade because of its causal link to the technologically important giant magnetoresistive effect (GMR). In addition, the phenomenon of indirect-exchange-mediated coupling provides a unique means of studying fundamental magnetic interactions. Of particular interest is the relationship between magnetic order in the interlayer material and the nature of the coupling across it. We have studied by polarized-neutron reflectometry a series of four superlattices of composition [30 Ni_.8Fe_.2(001) / x Fe(001)₉ sputter-deposited epitaxially on MgO(001), where x = 8, 9, 10, and 11 (~5.57.6 ML). The Fe interlayers assume the fcc structure of the permalloy layers. At room temperature in an applied field H=30 Oe, the magnetic structure of the superlattices passes from a parallel in-plane alignment of successive permalloy layers for the 8 and 9 -thick Fe interlayers to an anti-parallel alignment for 10 Fe (J_BL = 2.5 uJ/m²) weakening to 0.2 uJ/m² for the 11- interlayers. In none of the samples did we observe any evidence of magnetic order in the Fe interlayers. This is the first observation of magnetic coupling being mediated by a ferrous transition-metal interlayer.

Supported by ONR grant N00014-94-1-1146.