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Structure and magnetism in Cr-embedded Co nanoparticles

DOI: 10.1088/0953-8984/28/4/046003 DOI Help

Authors: Steve Baker (University of Leicester) , Mustafa Kurt (University of Leicester) , Mervyn Roy (Department of Physics and Astronomy, University of Leicester) , Martin Lees (University of Warwick) , Chris Binns (Department of Physics and Astronomy, University of Leicester)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of Physics: Condensed Matter , VOL 28

State: Published (Approved)
Published: February 2016
Diamond Proposal Number(s): 538 , 12400

Abstract: We present the results of an investigation into the atomic structure and magnetism of 2 nm diameter Co nanoparticles embedded in an antiferromagnetic Cr matrix. The nanocomposite films used in this study were prepared by co-deposition directly from the gas phase, using a gas aggregation source for the Co nanoparticles and a molecular beam epitaxy (MBE) source for the Cr matrix material. Co K and Cr K edge extended x-ray absorption fine structure (EXAFS) experiments were performed in order to investigate atomic structure in the embedded nanoparticles and matrix respectively, while magnetism was investigated by means of a vibrating sample magnetometer. The atomic structure type of the Co nanoparticles is the same as that of the Cr matrix (bcc) although with a degree of disorder. The net Co moment per atom in the Co/Cr nanocomposite films is significantly reduced from the value for bulk Co, and decreases as the proportion of Co nanoparticles in the film is decreased; for the sample with the most dilute concentration of Co nanoparticles (4.9% by volume), the net Co moment was 0.25 μ B/atom. After field cooling to below 30 K all samples showed an exchange bias, which was largest for the most dilute sample. Both the structural and magnetic results point towards a degree of alloying at the nanoparticle/matrix interface, leading to a core/shell structure in the embedded nanoparticles consisting of an antiferromagnetic CoCr alloy shell surrounding a reduced ferromagnetic Co core.

Journal Keywords: CoCr nanoparticles, magnetic nanoparticles

Subject Areas: Materials, Physics

Instruments: I18-Microfocus Spectroscopy

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