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In-situ magnetic force microscopy analysis of magnetization and demagnetization behavior in Al 3+ substituted Sr-hexaferrite

Rhein, F. and Helbig, T. and Neu, V. and Krispin, M. and Gutfleisch, O. (2018):
In-situ magnetic force microscopy analysis of magnetization and demagnetization behavior in Al 3+ substituted Sr-hexaferrite.
In: Acta Materialia, Elsevier Science Publishing, pp. 85-96, 146, ISSN 13596454,
DOI: 10.1016/j.actamat.2017.12.010,
[Online-Edition: https://doi.org/10.1016/j.actamat.2017.12.010],
[Article]

Abstract

The sintering temperature of an Al3+ substituted Sr-hexaferrite composite was systematically varied from 1180 °C to 1280 °C resulting in different microstructures. The grain size was found to range from a few hundred nanometers to several hundred micrometers depending on Al content and sintering temperature. Adding an Al substituted powder to a commercial powder increased the coercivity from 360 mT to 470 mT, at the same time, decreasing remanence from 350 mT to 305 mT. Magnetization and demagnetization processes from the thermally demagnetized state (TDS) and DC-demagnetized state (DCD) have been investigated systematically by in-situ magnetic force microscopy (MFM) under magnetic field. From the surface domain contrast a polarization was derived which quantitatively matches the global i.e. bulk polarization obtained by superconducting quantum interface device (SQUID) magnetometry. The shape of the initial polarization curve and the polarization from the DCD state were correlated with the in-situ MFM data revealing a distinctly different magnetization behavior depending on grain size. The presented results enable a better understanding of local nucleation mechanisms, global influences of pinning centers and further opportunities to improve rare earth (RE) free permanent magnets based on ferrites.

Item Type: Article
Erschienen: 2018
Creators: Rhein, F. and Helbig, T. and Neu, V. and Krispin, M. and Gutfleisch, O.
Title: In-situ magnetic force microscopy analysis of magnetization and demagnetization behavior in Al 3+ substituted Sr-hexaferrite
Language: English
Abstract:

The sintering temperature of an Al3+ substituted Sr-hexaferrite composite was systematically varied from 1180 °C to 1280 °C resulting in different microstructures. The grain size was found to range from a few hundred nanometers to several hundred micrometers depending on Al content and sintering temperature. Adding an Al substituted powder to a commercial powder increased the coercivity from 360 mT to 470 mT, at the same time, decreasing remanence from 350 mT to 305 mT. Magnetization and demagnetization processes from the thermally demagnetized state (TDS) and DC-demagnetized state (DCD) have been investigated systematically by in-situ magnetic force microscopy (MFM) under magnetic field. From the surface domain contrast a polarization was derived which quantitatively matches the global i.e. bulk polarization obtained by superconducting quantum interface device (SQUID) magnetometry. The shape of the initial polarization curve and the polarization from the DCD state were correlated with the in-situ MFM data revealing a distinctly different magnetization behavior depending on grain size. The presented results enable a better understanding of local nucleation mechanisms, global influences of pinning centers and further opportunities to improve rare earth (RE) free permanent magnets based on ferrites.

Journal or Publication Title: Acta Materialia
Volume: 146
Publisher: Elsevier Science Publishing
Uncontrolled Keywords: Hard magnetic materials, Sr-ferrite, Magnetization reversal mechanism, Domain structure, Magnetic force microscopy
Divisions: 11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences > Material Science > Functional Materials
11 Department of Materials and Earth Sciences
Date Deposited: 12 Mar 2018 10:24
DOI: 10.1016/j.actamat.2017.12.010
Official URL: https://doi.org/10.1016/j.actamat.2017.12.010
Funders: The authors wish to thank Dr. Thomas Berthold (Siemens AG) for the SEM analysis and Mathias Tonski (Tridelta Hartferitte GmbH) for provision of commercial ferrite powder., This work was supported by the German Federal Ministry of Education and Research (grant no 03X3582 - KomMa) and by the German federal state of Hessen through its LOEWE program "RESPONSE".
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