Magnetism of Co-rich clusters embedded in nanoporous Pd prepared by electrochemical dealloying - Influence of thermal annealing

Stefan Topolovec*, Alexander Steiner, Markus Gößler, Heinz Krenn, Roland Würschum

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Nanoporous palladium samples containing superparamagnetic Co-rich clusters were prepared by electrochemical dealloying and the magnetic properties were subsequently varied by thermal annealing at different temperatures. It is shown that in this way porous magnetic nanomaterials exhibiting various magnetic characteristics can be obtained. The as-dealloyed, unannealed sample is ferromagnetic at 4.2 K and superparamagnetic at 300 K, with a blocking temperature T B of 100 K. The observed general decrease of the magnetization with increased annealing temperature is explained by the redistribution of Co from the Co-rich superparamagnetic clusters into the Pd matrix, leading to a shrinkage of the clusters and the formation of a diluted Co–Pd alloy phase. As a consequence of the smaller magnetic cluster size a down-shift of T B occurs for annealing temperatures of 373 K and 573 K. After annealing at 773 K the stronger dissolution of Co from the clusters into the Pd-matrix reduces T B further down to 35 K. Additionally, a second blocked magnetic phase with much higher T B emerges, which leads to ferromagnetic behavior at room temperature. The occurrence of this phase is attributed to the formation of larger magnetic entities consisting of Co-rich clusters lying close together and a Co–Pd alloy phase with relatively high Co concentration in between these clusters. After high temperature annealing at 973 K a weakly ferromagnetic phase is obtained at 4.2 K and at 300 K, which can be explained by the nearly completed dissolution of the Co in the Pd matrix.

Original languageEnglish
Article number169802
JournalJournal of Magnetism and Magnetic Materials
Volume563
DOIs
Publication statusPublished - 1 Dec 2022

Keywords

  • Co–Pd alloy
  • Magnetic clusters
  • Nanocomposites
  • Nanoporous
  • Superparamagnetism
  • Thermal annealing

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics

Fields of Expertise

  • Advanced Materials Science

Cooperations

  • NAWI Graz

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