The microstructural evolution of chemical disorder and ferromagnetism in He + irradiated FePt 3 films

Grace L. Causer*, Hanliang Zhu, Joel Davis, Mihail Ionescu, Gary J. Mankey, Xiaolin L. Wang, Frank Klose

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

3 Scopus citations

Abstract

This paper investigates the role of ion-induced disorder on the morphology and magnetic properties of chemically ordered FePt 3 films. The effects are studied for 15 keV He + ions as a function of the ion fluence for 0, 2 × 10 16 and 2 × 10 17 ions cm −2 . Substitutional mixing of the L1 2 -type Fe-Pt sites takes place within the region of the chemically ordered FePt 3 film affected by the irradiation. This accompanies a paramagnetic-to-ferromagnetic transition, as determined by room-temperature magnetometry. Dark-field transmission electron microscopy (TEM) measurements confirm that the 15 keV He + ions induce a 120 nm-thick chemically disordered layer into the sub-surface region of the nominally 280 nm-thick ordered FePt 3 film. The average domain size and the fractional density of the chemically ordered domains within the irradiated FePt 3 microstructure are found to mutually decrease with increasing ion fluence. Selected-area electron diffraction results demonstrate that the film's single crystallinity is preserved after irradiation, irrespective of the ion fluence. High-resolution TEM elucidates the coexistence of ordered domains and precipitate disordered domains in the near-surface, low-ion impacted regions of the FePt 3 film. Collectively, this work provides detailed insights into the material-science relationship between ion-induced disorder and ferromagnetism in FePt 3 , as a step towards creating fully customisable, ion-beam-synthesised magnetic nano-elements.

Original languageEnglish
Pages (from-to)672-677
Number of pages6
JournalApplied Surface Science
Volume459
DOIs
StatePublished - 30 Nov 2018

Keywords

  • Bit patterned media
  • Chemical disorder
  • Ferromagnetism
  • Ion fluence
  • Ion irradiation
  • Thin film

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