The FePd alloy system can exhibit the L1₀ chemically ordered phase when the Fe:Pd stoichiometry of the alloy is near 1:1.[1] The crystallographic structure of the L1₀ ordered alloy is characterized by alternating Fe and Pd atomic layers along a cubic stacking direction, which as a consequence suffers a tetragonal distortion. This tetragonal distortion induces a strong perpendicular magnetic anisotropy (PMA) when the layering is parallel to the film plane and the material is in thin film form. The origin of the strong PMA is the large spin-orbit coupling of the paramagnetic Pd atoms and a strong hybridization of their 4d bands with the highly polarized Fe 3d bands.[2] Although the mechanism of PMA is well known, controlling it in thin film form is non-trivial and warrants further study to be useful in applications such as magneto-recording media.

We will report on our correlated studies of the magnetic domain structure with the PMA in epitaxial Au / FePd(001) / MgO(001) thin films. Epitaxial FePd thin films were grown using magnetron sputtering in an ultra-high vacuum deposition system at elevated temperatures (400 – 600 °C) and on MgO(001) substrates to achieve highly ordered films with strong PMA. The films were subsequently capped with Au at room temperature (RT) to prevent oxidation, and alteration of the magnetic anisotropy.[3] Reflection high energy electron diffraction was used in situ to monitor the epitaxial growth and x-ray diffraction techniques were used ex situ to monitor the chemical ordering of the films. Magnetic anisotropy values were obtained from hysteresis loops measured at RT using a Superconducting Quantum Interference Device magnetometer and also by ferromagnetic resonance scans. The magnetic domain structure was investigated using a Nanotec scanning probe microscope with a magnetically coated tip in non-contact mode. These studies have improved our understanding of these strong PMA materials, enabling correlations between the observed domain structure and the magnetic anisotropy, along with comparison to models of domain structure.[4]

[1] T. B. Massalski et al. (eds.), Binary Alloy Phase Diagrams, (ASM International, 1990), p. 1751.

[2] A. Cebollada et al., Magnetic Nanostructures, edited by H. S. Nalwa (American Scientific Publishers, 2002), pp. 94-100.

[3] C. Clavero et al., Appl. Phys. Lett. 92, 162502 (2008).

[4] A. Hubert and R. Schafer, Magnetic Domains The Analysis of Magnetic Microstructures (Springer, 2000), pp. 107-354.

This work was supported by the Virginia Space Grant Consortium, National Science Foundation (DMR Grant #0355171), the American Chemical Society (PRF Grant #41319-AC), and the Research Corporation Cottrell Scholar Award.