Magnetostructural effects in exchange-spring nanocomposite magnets probed by combined X-ray & neutron scattering

Priyank Shyam, Jakob Voldum Ahlburg, Anna Zink Eikeland, Matilde Saura-Múzquiz, Mogens Christensen

Research output: Contribution to conferencePosterResearch

Abstract

An ideal permanent magnet should be highly resistant to demagnetization (high coercivity HC) and have a high value of maximum internal magnetization (high saturation magnetization MS). In the real world, a single-phase magnet might not simultaneously possess high values of these magnetic properties. It is usually observed that rare-earth-free permanent magnets have either high HCwith low MS (‘hard’ magnet– hard to demagnetize) or, low HCwith high MS (‘soft’ magnet). The hexaferrite compound SrFe12O19 has relatively high HC (due to pronounced magnetocrystalline anisotropy) – making it a ‘hard magnetic’ phase, but a higher MS value would be highly appreciated.[1] Spinel ferrites (AB2O4type) on the other hand, are ‘soft magnetic’ phases i.e. low HC, but potentially strongly magnetic. Enhancement of HC and MSvalues simultaneously could be achieved by the mixing of two different nanomagnetic phases (hard-soft composite) – known as an exchange-spring nanocomposite.[2,3] The resultant magnetic properties of such composites would be hierarchically emergent – arising from the underlying atomic structure, via the nanoscale morphology of the individual particles, to the microscopic structural coupling of the different phases. While various studies have focused on the synthesis of exchange-spring magnets and their magnetic characterizations, detailed structural investigations are limited.[3–5] We report a comparative investigation on exchange-spring nanocomposites of SrFe12O19(SFO – hard magnet) and Zn0.2Co0.8Fe2O4(ZCFO – soft magnet) prepared by two different synthesis routes: mechanical powder mixing and sol-gel coating. M-H loops from VSM magnetometry showed a dependence of the exchange-coupling behavior on the technique used for nanocomposite formation. Crystallographic and magnetic structure of the samples were analyzed by combined Rietveld refinement of data from synchrotron X-ray diffraction (SR-XRD performed at MS X04SA beamline @ SLS) & thermal neutron powder diffraction (NPD performed using HRPT diffractometer at SINQ spallation source @ PSI). The difference in the scattering interaction for X-rays and neutrons allowed for complementary, robust & accurate structural analysis.[5,6] Combined Rietveldrefinement of SR-XRD and NPD data of the nanocomposites enabled extraction of accurate values for lattice parameters, atomic positions, thermal motion, cation distribution, magnetic moments and microstructure. A detailed understanding of these correlated magnetostructural properties would be instrumental towards improving the performance of permanent magnets based on exchange-spring nanocomposites.


References:

[1]       R. C. Pullar, Prog.Mater.Sci. 2012,57, 1191.

[2]       E.F. Kneller, R. Hawig, IEEE Trans. Magn. 1991, 27, 3588.

[3]       F. Liu, Y.Hou, S. Gao, Chem. Soc. Rev. 2014, 43, 8098.

[4]       S. Hirosawa, J.Magn. Soc. Japan 2015, 39, 85.

[5]       S. M. Yusuf,A. Kumar, Appl. Phys. Rev. 2017, 4, 031303.

[6]       E. Solano, C.Frontera, T. Puig, X. Obradors, S. Ricart, J. Ros, J. Appl. Crystallogr.2014, 47, 414.

Original languageEnglish
Publication date27 Aug 2019
Publication statusPublished - 27 Aug 2019
EventJoint European Magnetic Symposia 2019 - Uppsala Konsert & Kongress, Uppsala, Sweden
Duration: 26 Sept 201930 Sept 2019
https://jems2019.se/

Conference

ConferenceJoint European Magnetic Symposia 2019
LocationUppsala Konsert & Kongress
Country/TerritorySweden
CityUppsala
Period26/09/201930/09/2019
Internet address

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