Structure and Magnetism of Co2Ge Nanoparticles

Authors

Onur Tosun, University of DelawareFollow
Frank M. Abel, University of DelawareFollow
Balamurugan Balasubramanian, University of Nebraska-LincolnFollow
Ralph Skomski, University of Nebraska-LincolnFollow
David J. Sellmyer, University of Nebraska - LincolnFollow
George C. Hadjipanayis, University of DelawareFollow

ORCID IDs

Frank M. Abel

Document Type

Article

Date of this Version

2019

Citation

Nanomaterials 2019, 9, 1371

Comments

© 2019 by the authors.

Open access

doi:10.3390/nano9101371

Abstract

The structural and magnetic properties of Co₂Ge nanoparticles (NPs) prepared by the cluster-beam deposition (CBD) technique have been investigated. As-made particles with an average size of 5.5 nm exhibit a mixture of hexagonal and orthorhombic crystal structures. Thermomagnetic measurements showed that the as-made particles are superparamagnetic at room temperature with a blocking temperature (T_B) of 20 K. When the particles are annealed at 823 K for 12 h, their size is increased to 13 nm and they develop a new orthorhombic crystal structure, with a Curie temperature (T_C) of 815 K. This is drastically different from bulk, which are ferromagnetic at cryogenic temperatures only. X-ray diffraction (XRD) measurements suggest the formation of a new Co-rich orthorhombic phase (OP) with slightly increased c/a ratio in the annealed particles and this is believed to be the reason for the drastic change in their magnetic properties.