Gerina Marianna, Sanna Angotzi Marco, Mameli Valentina, Gajdošová Veronika, Rainer Daniel N, Dopita Milan, Steinke Nina-Juliane, Aurélio David, Vejpravová Jana, Zákutná Dominika
Department of Inorganic Chemistry, Faculty of Science, Charles University Hlavova 2030/8 128 43 Prague 2 Czech Republic
Department of Chemical and Geological Sciences, University of Cagliari S.S. 554 bivio per Sestu, 09042 8 Monserrato CA Italy.
Nanoscale Adv. 2023 Aug 3;5(17):4563-4570. doi: 10.1039/d3na00266g. eCollection 2023 Aug 24.
The magnetic properties of nanoscale magnets are greatly influenced by surface anisotropy. So far, its quantification is based on the examination of the blocking temperature shift within a series of nanoparticles of varying sizes. In this scenario, the surface anisotropy is assumed to be a particle size-independent quantity. However, there is no solid experimental proof to support this simplified picture. On the contrary, our work unravels the size-dependent magnetic morphology and surface anisotropy in highly uniform magnetic nanoparticles using small-angle polarized neutron scattering. We observed that the surface anisotropy constant does not depend on the nanoparticle's size in the range of 3-9 nm. Furthermore, our results demonstrate that the surface spins are less prone to polarization with increasing nanoparticle size. Our study thus proves the size dependence of the surface spin disorder and the surface anisotropy constant in fine nanomagnets. These findings open new routes in materials based on a controlled surface spin disorder, which is essential for future applications of nanomagnets in biomedicine and magnonics.
纳米级磁体的磁性受到表面各向异性的极大影响。到目前为止，其量化是基于对一系列不同尺寸纳米颗粒内阻塞温度偏移的研究。在这种情况下，表面各向异性被假定为与颗粒尺寸无关的量。然而，并没有确凿的实验证据支持这一简化的图景。相反，我们的工作利用小角极化中子散射揭示了高度均匀的磁性纳米颗粒中与尺寸相关的磁形态和表面各向异性。我们观察到，在3 - 9纳米范围内，表面各向异性常数并不依赖于纳米颗粒的尺寸。此外，我们的结果表明，随着纳米颗粒尺寸的增加，表面自旋极化的倾向降低。因此，我们的研究证明了精细纳米磁体中表面自旋无序和表面各向异性常数对尺寸的依赖性。这些发现为基于可控表面自旋无序的材料开辟了新途径，这对于纳米磁体在生物医学和磁子学中的未来应用至关重要。
