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

Abstract

<p class="MsoNoSpacing" style="text-align:justify">An ideal permanent magnet should be highly resistant to demagnetization (high coercivity <i>H</i>_C) and have a high value of maximum internal magnetization (high saturation magnetization <i>M</i>_S). 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 <i>H</i>_Cwith low <i>M</i>_S (‘hard’ magnet– hard to demagnetize) or, low <i>H</i>_Cwith high <i>M</i>_S (‘soft’ magnet). The hexaferrite compound SrFe₁₂O₁₉ has relatively high <i>H</i>_C (due to pronounced magnetocrystalline anisotropy) – making it a ‘hard magnetic’ phase, but a higher <i>M</i>_S value would be highly appreciated.^[1] Spinel ferrites (AB₂O₄type) on the other hand, are ‘soft magnetic’ phases <i>i.e. </i>low <i>H</i>_C, but potentially strongly magnetic. Enhancement of <i>H</i>_C and <i>M</i>_Svalues 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 Zn_0.2Co_0.8Fe₂O₄(ZCFO – soft magnet) prepared by two different synthesis routes: mechanical powder mixing and sol-gel coating. <i>M</i>-<i>H</i> 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) &amp; 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 &amp; 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.</p><p class="MsoNoSpacing" style="text-align:justify"><br/></p><p class="MsoNoSpacing" style="text-align:justify">References:</p><p class="MsoNormal" style="margin-left:32.0pt;text-indent:-32.0pt;mso-pagination:none;mso-layout-grid-align:none;text-autospace:none">[1]       R. C. Pullar, <i>Prog.</i><i>Mater.Sci.</i> <b>2012</b>,<i>57</i>, 1191.</p><p class="MsoNormal" style="margin-left:32.0pt;text-indent:-32.0pt;mso-pagination:none;mso-layout-grid-align:none;text-autospace:none">[2]       E.F. Kneller, R. Hawig, <i>IEEE Trans. Magn.</i> <b>1991</b>, <i>27</i>, 3588.</p><p class="MsoNormal" style="margin-left:32.0pt;text-indent:-32.0pt;mso-pagination:none;mso-layout-grid-align:none;text-autospace:none">[3]       F. Liu, Y.Hou, S. Gao, <i>Chem. Soc. Rev.</i> <b>2014</b>, <i>43</i>, 8098.</p><p class="MsoNormal" style="margin-left:32.0pt;text-indent:-32.0pt;mso-pagination:none;mso-layout-grid-align:none;text-autospace:none">[4]       S. Hirosawa, <i>J.Magn. Soc. Japan</i> <b>2015</b>, <i>39</i>, 85.</p><p class="MsoNormal" style="margin-left:32.0pt;text-indent:-32.0pt;mso-pagination:none;mso-layout-grid-align:none;text-autospace:none">[5]       S. M. Yusuf,A. Kumar, <i>Appl. Phys. Rev.</i> <b>2017</b>, <i>4</i>, 031303.</p><p class="MsoNormal" style="margin-left:32.0pt;text-indent:-32.0pt;mso-pagination:none;mso-layout-grid-align:none;text-autospace:none">[6]       E. Solano, C.Frontera, T. Puig, X. Obradors, S. Ricart, J. Ros, <i>J. Appl. Crystallogr.</i><b>2014</b>, <i>47</i>, 414.</p>

Topics

• nanocomposite
• impedance spectroscopy
• morphology
• compound
• phase
• extraction
• mass spectrometry
• magnetization
• saturation magnetization
• coercivity
• neutron scattering
• static light scattering
• synchrotron radiation X-ray diffraction