Pergamon Acta mater. Vol. 46, No. 7, pp. 2299-2303, 1998 0 1998 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved Printed in Great Britain PXI: Sl359~~97~385~ 1359~6454/98 $19.00 + 0.00 zyxwvutsrqpo BUFFER LAYER MORPHOLOGY EFFECTS ON THE ORDERING OF EPITAXIAL FePd(OO1) THIN FILMS P. CARO, A. CEBOLLADA, D. RAVELOSONA, J. TAMAYO, R. GARCiA and F. BRIONES IMM (CNM/CSIC) and UAM, Isaac Newton 8 PTM, 28760 Tres Cantos, 28006 Madrid, Spain Abstract-The structural properties of thin FePd(OO1) films grown on MgO(100) substrates by UHV t~ode-sputtering have been studied as a function of the morphoiogy of the substrate/seed layer interface. Changes in short range ordering are found to be correiated with the thickness of the Pt seed layer which controls the interface morDholoev and the formation of order domains in the FePd alloy along the growth direction. 0 1998 Acta ketallu&ica Inc. 1. INTRODUCTION New nanostructured magnetic materials with extra- ordinary properties such as giant magnetoresistance, oscillatory magnetic coupling, or large perpendicu- lar magnetic anisotropies can be synthesized in single crystalline thin film form by means of epitax- ial techniques such as molecular beam epitaxy (MBE). Surface kinetics aspects related to the par- ticular growth technique and growth conditions used are very important for determining structural and consequent physical properties of the nanos- tructures. Obviously, an important factor for epi- taxy is the compatibility of substrate lattice parameter and crystal symmetry with that of the grown layer. However, many recently published results show also the determinant role of the specific properties of the substrate/epitaxial layer interface. In particular, in order to grow crystalline metallic magnetic films on insulating substrates of techno- logical impact like semiconductors or oxides, an appropriate conditioning or buffering of the inter- face is necessary. found in MBE Pt (001) films grown at 700°C on MgO(l00) [4]. It is obvious that the strength of the interfacial chemical bond is important in the kind of growth of a metal on a ionic crystal, and it has been compared for the Au/MgO vs Au/NaCl system [5]. Once the seeding epitaxy technique for metals is controlled, the study of many materials systems with different crystalline orientations and structures can be performed. For the magnetic materials, and both from the basic research and technological points of view, research in systems exhibiting both high magnetocrystalline anisotropy and magneto- optic effects is of great importance. Chemical order- ing is a relevant topic in the study of metallic binary alloys in which one of the constituents is magnetic. New magnetic properties, such as strong magnetic anisotropies or enhancement in the mag- neto-optical activity, are predicted [6] and observed in the presence of an ordered phase f7-137. Several substrates are used for growing metallic thin films, like oxides, such as MgO, zirconia or sapphire. Many of these materials have typically big terraces on which a seed layer of a metal is grown at a certain temperature, to obtain a flat, single crystalline material. For example, Lairson et al. [l] have shown that single crystalline Pt thin films with different orientations can be grown by planar mag- netron sputtering onto heated substrates. They have found that under their growth conditions, a 0.3 nm Fe layer grown onto MgO prior to deposition of Pt yields to (001) epitaxial films with no (111) orien- tations. On the other hand, McIntyre et ~2. [2,3] find that e-beam evaporated Pt films have a mixture of crystallites having (111) and (001) orientation over a range of substrate temperatures from 25 to 7OO”C, with the (111) orientation dominant at low substrate temperatures. This epitaxial growth is also Ordering in polycrystalline or single crystalline bulk samples is usually obtained by prolonged annealing of disordered alloys, making use of bulk atomic diffusion. Examples of alternative pro- cedures are the annealing of multilayered samples [S] or the atomically controlled MBE deposition of alternating species 19-I 11. In the same way as in the fabrication of semiconductor ordered alloys, code- position of the elements at elevated substrate tem- peratures can lead to highly ordered, single crystalline metallic alloys [7,12,13]. Direct depo- sition on MgO does not lead to an ordered phase ]13], The interface has to be modified by add- ing a Pt seed layer to allow the correct epitaxy. In our particular case, FePd alloys are known to adopt the ordered CuAu (I) structure. It consists of monoatomic planes of pure Fe and Pd stacked along the (001) direction in a face centered cubic lattice, in contrast to the disordered phase that is a solution of randomly positioned Fe and Pd atoms