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

Research output: Contribution to journalArticle

6 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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