Modulation of magnetic anisotropy through self-assembled surface nanoclusters: Evolution of morphology and magnetism in Co–Pd alloy films

Chuan Che Hsu, Hsiang Chih Chiu*, Venkata Ramana Mudinepalli, Yu Chuan Chen, Po Chun Chang, Chun Te Wu, Hung Wei Yen, Wen Chin Lin

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

7 Citations (Scopus)

Abstract

In this study, the self-assembly of surface nanoclusters on 10–20-nm-thick Co 50 Pd 50 (Co–Pd) alloy thin films deposited on the Al 2 O 3 (0001) substrate was systematically investigated. The time-dependent evolution of the nanocluster size and magnetic properties was monitored using an atomic force microscope (AFM) and the magneto-optical Kerr effect. When the Co–Pd alloy films were stored in an ambient environment, small nanodots gradually gathered to form large nanoclusters. Approximately 30 days after growth, a nanocluster array formed with an average lateral size of 100 ± 20 nm and average height of 10 ± 3 nm. After 100 days, the average lateral size and average height had increased to 140 ± 20 and 25 ± 5 nm, respectively. The AFM phase image exhibited a structured contrast on the nanocluster surface, indicating the nonuniform stiffness distribution of the nanoclusters. A microscopic Auger spectroscopy measurement suggested that in contrast to the Pd-rich signal in the flat area, the nanoclusters were cobalt- and oxygen-rich areas. Cross-sectional investigation through transmission electron microscopy coupled with energy dispersive spectroscopy showed that the nanoclusters were mostly composed of Co oxide. A uniform Pd-rich underlayer had been maintained underneath the self-assembled Co-oxide nanoclusters. With the formation of a Co-oxide nanocluster array and Pd-rich underlayer, the magnetic easy axis of the Co–Pd film gradually altered its direction from the pristine perpendicular to in-plane direction. Because of the change in the magnetic easy axis, the hydrogenation-induced spin-reorientation transition was suppressed with the evolution of the surface Co-oxide nanoclusters.

Original languageEnglish
Pages (from-to)133-143
Number of pages11
JournalApplied Surface Science
Volume416
DOIs
Publication statusPublished - 2017 Sep 15

Keywords

  • Hydrogenation
  • Magnetism
  • Surface nanostructure
  • Thin film

ASJC Scopus subject areas

  • Chemistry(all)
  • Condensed Matter Physics
  • Physics and Astronomy(all)
  • Surfaces and Interfaces
  • Surfaces, Coatings and Films

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