| AVS 60th International Symposium and Exhibition | |
| Magnetic Interfaces and Nanostructures | Monday Sessions |
| Session MI+EM+MG-MoA |
| Session: | Frontiers of Complex Oxides |
| Presenter: | M.A. Steiner, University of Virginia |
| Authors: | M.A. Steiner, University of Virginia R.B. Comes, University of Virginia J.A. Floro, University of Virginia W.A. Soffa, University of Virginia J.M. Fitz-Gerald, University of Virginia |
| Correspondent: | Click to Email |
Thin films of 3d-4d/5d magnetic alloys such as Fe-Pt, Co-Pt, and Fe-Pd are of technological interest due to their ordered L10 tetragonal intermetallic phase which exhibits a high magnetocrystalline anisotropy of K ~ 107 to 108 ergs/cm3, comparable to that of 3d-4f rare earth magnets. Strong hard-magnet properties, combined with the ductility and chemical inertness from their ennobled metallic nature, make these alloys ideal for applications in ultra-high-density magnetic storage or micro-electro-mechanical systems where the thermally induced KV/kBT superparamagnetic limit is an important constraint. The Co-Pt system has been shown to decompose under bulk conditions into a novel, strain-induced chessboard microstructure at the eutectoid composition between its ordered L10 and L12 intermetallic phases, and related 3d-4d/5d material systems may also be expected to produce strain-induced microstructural behavior. Within this class of materials, Fe-Pd alloys possess comparatively moderate magnetocrystalline anisotropies relative to Co-Pt and Fe-Pt. The Fe-Pd phase diagram, however, exhibits a considerably lower order-disorder transition temperature range that renders the material well-suited for nanostructured magnetic applications by enabling lower processing temperatures.
Epitaxial films of Fe38.5Pd61.5 at the L10-L12 eutectoid composition have been grown on MgO (001) oriented substrates by pulsed laser deposition. It is found that ordered thin films of Fe38.5Pd61.5 are deposited as a single phase, initially surmised to be L12 due magnetic data and the location and orientation of the X-Ray Diffraction (XRD) peaks. Careful analysis of peak intensities, however, results in an anomalously large long-range ordering parameter. Quantitative XRD analysis of the films shows that this is due to a perturbation in the Pd-site occupancy of the non-stoichiometric Fe atoms in the films; resulting in a hybridization of the L10 and L12 ordered structures. This L1'hybridized ordered structure, first postulated by thermodynamic principles to exist for the Au-Cu system†, is believed to be induced by the accommodation of epitaxial strain from the substrate. In addition to its verification, the thermodynamic behavior of this new strain-induced phase is addressed in relation to the equilibrium phase diagram.
† W. Shockley, J. Chem. Phys. 6, 130 (1938)