Phase transition from the ferromagnetic to superparamagnetic with a loop shift in 5-nm nickel particles

Xiansong Liu, Kai Huang, Shengqiang Zhou, Peng Zhao, Udi Meridor, Aviad Frydman, Aharon Gedanken

Research output: Contribution to journalArticlepeer-review

14 Scopus citations

Abstract

Monodispersed 5-nm nickel particles have been successfully prepared by the microwave-assisted polyol method and confirmed by TEM and HRTEM analysis. Magnetic hysteresis loops, measured at different temperatures from 4.2 to 300 K after the sample was cooled from 300 K with a 20 kOe field, have found to occur at the temperature of a phase transition, Tpt = 100 K, i.e., the temperature at which the ferromagnetic to superparamagnetic transition was observed. It is unexpected for magnetic nanoparticles that the loop shift both zero-field cooling and field cooling occurs above Tpt and it is perfectly symmetrical below the temperature. The large shift observed may suggest the existence of the disfigurement and small cavities of nanoparticles, which cause surface spin disorder or canting above Tpt.

Original languageEnglish
Pages (from-to)504-508
Number of pages5
JournalJournal of Magnetism and Magnetic Materials
Volume305
Issue number2
DOIs
StatePublished - Oct 2006

Bibliographical note

Funding Information:
This work was supported by the Key Program of the Education Department of Anhui Province under Grant no. 2005KJ033ZD.

Keywords

  • Loop shift
  • Magnetic hysteresis loop
  • Superparamagnetic

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