Issue 17, 2020

Exploring the direct synthesis of exchange-spring nanocomposites by reduction of CoFe2O4 spinel nanoparticles using in situ neutron diffraction

Abstract

In situ neutron powder diffraction (NPD) was employed for investigating gram-scale reduction of hard magnetic CoFe2O4 (spinel) nanoparticles into CoFe2O4/CoFe2 exchange-spring nanocomposites via H2 partial reduction. Time-resolved structural information was extracted from Rietveld refinements of the NPD data, revealing significant changes in the reduction kinetics based on the applied temperature and H2 available. The nanocomposite formation was found to take place via the following two-step reduction process: CoxFe3−xO4 → CoyFe1−yO → CozFe2−z. The refined lattice parameters and site occupation fractions indicate that the reduced phases, i.e. CoyFe1−yO and CozFe2−z, initially form as Co-rich compounds (i.e. y > 0.33 and z > 1), which gradually incorporate more Fe as the reduction proceeds. The reduction depletes the Co-content in the parent spinel, which may end up becoming magnetically soft Fe3O4 at high temperature (T = 542 °C), while at lower temperatures there may be a co-existence of Fe3O4 and γ-Fe2O3 or CoxFe3−xO4. The macroscopic magnetic properties of the products were measured by vibrating sample magnetometry (VSM) and revealed the hard and soft magnetic domains in the nanocomposites to be effectively exchange-coupled. An increase of approximately 70% in specific saturation magnetisation, remanence magnetisation, and coercivity compared to the parent CoFe2O4 material was achieved for the best sample.

Graphical abstract: Exploring the direct synthesis of exchange-spring nanocomposites by reduction of CoFe2O4 spinel nanoparticles using in situ neutron diffraction

Supplementary files

Article information

Article type
Paper
Submitted
02 Febr. 2020
Accepted
14 Apr. 2020
First published
15 Apr. 2020

Nanoscale, 2020,12, 9440-9451

Exploring the direct synthesis of exchange-spring nanocomposites by reduction of CoFe2O4 spinel nanoparticles using in situ neutron diffraction

J. V. Ahlburg, C. Granados-Miralles, F. H. Gjørup, H. L. Andersen and M. Christensen, Nanoscale, 2020, 12, 9440 DOI: 10.1039/D0NR00912A

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements