Modification of local order in FePd films by low energy He + irradiation

• Published in: Journal of applied physics Vol. 104; no. 1; pp. 013901 - 013901-6
• Main Authors: Merkel, D. G., Tanczikó, F., Sajti, Sz, Major, M., Németh, A., Bottyán, L., Horváth, Z. E., Waizinger, J., Stankov, S., Kovács, A.
• Format: Journal Article
• Language: English
• Published: United States American Institute of Physics 01.07.2008
• Subjects: ANISOTROPY; COBALT ALLOYS; CRYSTAL GROWTH; ELECTRON SPECTRA; FCC LATTICES; HELIUM IONS; ION BEAMS; IRON ALLOYS; KEV RANGE 100-1000; LATTICE PARAMETERS; MAGNESIUM OXIDES; MAGNETIC PROPERTIES; MATERIALS SCIENCE; MOESSBAUER EFFECT; MOLECULAR BEAM EPITAXY; ORDER PARAMETERS; PALLADIUM ALLOYS; PHASE TRANSFORMATIONS; TEMPERATURE RANGE 0273-0400 K; THIN FILMS; X-RAY DIFFRACTION
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.2938027

Owing to their strong perpendicular magnetic anisotropy, FePd, CoPd, and their Co(Fe)Pt counterparts are candidate materials for ultrahigh density magnetic recording. The stability and magnetic properties of such films are largely dependent on the orientation and local distribution of the L 1 0 FePd phase fraction. Therefore, the formation and transformation of the L 1 0 phase in such thin films have been the subject of continued interest. Highly ordered epitaxial FePd(001) thin films (with an L 1 0 phase fraction of 0.81) were prepared by molecular-beam epitaxy on a MgO(001) substrate. The effect of postgrown room temperature, 130 keV He + irradiation was investigated at fluences up to 14.9 × 10 15   ions / cm 2 . X-ray diffraction and conversion electron Mössbauer spectroscopy revealed that with increasing fluence, the L 1 0 FePd phase decomposes into the face centered cubic phase with random Fe and Pd occupation of the sites. A partially ordered local environment exhibiting a large hyperfine magnetic field also develops. Upon He + irradiation, the lattice parameter c of the FePd L 1 0 structure increases and the long range order parameter S steeply decreases. The Fe-Fe nearest-neighbor coordination in the Fe-containing environments increases on average from Fe 47 Pd 53 to Fe 54 Pd 46 , indicating a tendency of formation iron-rich clusters. The equilibrium parameters corresponding to the equiatomic L 1 0 phase were found at different fluences by conversion electron Mössbauer spectroscopy and by x-ray diffraction a difference, from which a plane-perpendicular compressive stress and a corresponding in-plane tensile stress are conjectured. The steep increase in the interface roughness above 7.4 × 10 15   ions / cm 2 is interpreted as a percolation-type behavior related to the high diffusion anisotropy in the L 1 0 phase.