Magnetic, transport and structural properties of Co/Ir multilayers grown by molecular beam epitaxy

Abstract

We report on the structural properties of a [Co30/Ir10]10× (Å) superlattice, as well as on the magnetic and transport properties of a Co15/Ir5/Co30 (Å) artificial ferrimagnetic system. The samples were grown by molecular beam epitaxy (MBE) on MgO(001) substrates covered with a Ir130 (Å) buffer layer. High resolution cross section and plan view transmission electron microscopy (TEM) images present a high quality epitaxial stack [100]MgO(001) ‖ [100]Ir(001) ‖ [100]Co(001), with a tetragonalization of the Co fcc structure, due to strains induced by the Ir buffer. TEM images also show that the Co/Ir interfaces are flat, while the layers are continuous and free of bridges. These observations are consistent with zero field nuclear magnetic resonance measurements which indicate an fcc structure of the Co layers, and an interface mixing between Co and Ir limited to one atomic layer. As a consequence the antiferromagnetically coupled Co/Ir/Co sandwich presents large saturation and coercive fields which exceed 20 kOe and 220 Oe, respectively. Annealing made on the same sandwich indicate that the magnetic and transport properties are stable up to 300 °C. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)