Istituto dei materiali per l'elettronica ed il magnetismo     
Lupo P., Casoli F., Albertini F., Nasi L., Ranzieri P., Fabbrici S., Bocchi C., Orna J., Algarabel P., Morellon L. Optimization of FePt film morphology for spintronic devices. In: Magnet '09 - Magnet '09 - I convegno nazionale di magnetismo (Roma, 27/29 ottobre 2009).
The FePt L10-alloy has attracted wide interest for its basic and application-oriented properties [1]. The large magnetocrystalline anisotropy of this alloy could be in fact exploited in thermally stable electrodes for magnetic tunnel junctions (MTJs). For this reason, the study of surface quality in thin FePt films for MTJs electrodes is largely important [2]. In this work we prepare well-ordered epitaxial films with perpendicular easy-axis orientation, and modify film morphology and surface roughness in a controlled way by varying growth temperature and in situ annealing time, and changing the substrate. FePt films with thickness 10 and 15 nm have been grown by RF sputtering on heated MgO(100), SrTiO3(100) and LSAT(100), by alternating the deposition of very thin Fe and Pt layers with nominal thickness of about 0.2 nm. The growth temperature has been varied in the range 390 - 460 C, and the effects of in situ annealing treatments performed at the same temperature as the growth temperature for increasing time (up to 115 minutes) have been studied. A complete structural and morphological characterisation has been carried out by X-Ray Diffraction, Transmission Electron Microscopy, High Angle Annular Dark Field and Energy Dispersive X-ray Spectroscopy in scanning mode, Atomic Force Microscopy. The magnetic properties of the samples have been studied by Alternating Gradient Force and SQUID Magnetometry. In the considered range of growth temperatures FePt grows epitaxially on MgO and SrTiO3 with (001) orientation, and the alloy shows a high degree of chemical order, which can be improved by in situ annealing. On the other hand, unsatisfactory results have been obtained when growing FePt on a LSAT substrate. Due to the different FePt mismatch with MgO and SrTiO3, the films morphology at fixed growth temperature is largely influenced by the underlying substrate. The optimization of the growth parameters has allowed us to obtain FePt layers of 15 nm with high chemical order, high perpendicular coercivity (from a few kOe to tens of kOe), and roughness less than 1 nm. The role of lattice mismatch in determining structure, morphology and magnetic properties will be discussed.
Subject Magnetic Recording
FePt alloy

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