Self-Diffusion of Iron in L10 FePd films Upon He-irradiation (alternative title: An alternative for diffusion studies in isotopic FePd multilayers)

TL;DR

This study investigates the self-diffusion of iron in L10 FePd thin films under helium ion irradiation, revealing phase-dependent diffusion pathways and coefficients crucial for magnetic storage material optimization.

Contribution

It provides the first detailed analysis of iron self-diffusion in L10 FePd films using isotope-periodic multilayers and Mössbauer spectroscopy, highlighting phase-specific diffusion behaviors.

Findings

Diffusion occurs mainly via iron-rich regions.

Diffusion length ratios are 1:1.4:5.6 for L10, fcc, and iron-rich phases.

Diffusion coefficient in the c-direction of L10 is over 1.9 times lower than in the a-b plane.

Abstract

The continuous need towards improving the capacity of magnetic storage devices requires materials with strong perpendicular magnetic anisotropy. FePd, CoPd and their Co(Fe)Pt counterparts very attractive candidate for such purposes. The magnetic properties of these films are largely dependent on the orientation and local distribution of the L10 FePd phase fraction which are mainly controlled by diffusion processes and involve diffusion paths of a few angstroms. Highly ordered as well as disordered epitaxial isotope-periodic 57FePd/natFePd (001) thin films were prepared by molecular-beam epitaxy on MgO(001) substrate. Short range diffusion of different phases in FePd thin film induced by room temperature 130 keV He+ irradiation was investigated at fluences up to 30\times1015 ions/cm2. Conversion electron M\"ossbauer spectroscopy and synchrotron M\"ossbauer reflectivity experiments showed that the inter-atomic diffusion across 57FePd/natFePd interface occur mainly via the iron rich regions. The ratio of the diffusion length in the L10, fcc and iron rich structure are 1:1.4:5.6 respectively. Assuming that the diffusion coefficient in the fcc phase is between the diffusion coefficient of the L10 phase in the crystallographic c direction and perpendicular to it, the diffusion coefficient in the c-direction of the L10 phase is found more than 1.9 times lower than in the a-b plane.