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Keynote Lecture

WEB Field-Dependence of Magnetic Disorder in Nanoparticles

Wednesday (23.09.2020)
16:10 - 16:40 Z: Special Symposia I
Part of:


Magnetic nanoparticles have peculiar magnetic properties that make them relevant for data storage, electronic and mechanical engineering, and biomedical applications. Being intrinsic to nanomaterials, disorder effects crucially determine the magnetization properties. It has been recently shown that the heating performance of magnetic nanoparticles is strongly impacted by disorder effects [1-3]. However, despite the great technological relevance and fundamental importance, it is challenging to isolate surface-related effects from the effective magnetic features of the bulk. Fundamentally, these issues demand to reveal the three-dimensional magnetic configuration and the nanoscale distribution of spin disorder within magnetic nanoparticles.

 

Polarized small-angle neutron scattering (SANS) is a versatile technique allowing us to investigate the nanoparticle magnetization with great detail [4]. Within this contribution, I will give an overview of our recent studies on the intraparticle spatial magnetization distribution in ferrite nanospheres [5]. I will show that we revealed a significant field-dependence of the integral nanoparticle moment, which is in contrast with the classical, static picture of a collinearly magnetized nanoparticle core with a structurally disordered shell accompanied by magnetically disordered surface spins. Moreover, we demonstrate how magnetic order can overcome the structural disorder. Polarized SANS extends the traditional macroscopic characterization by revealing the local magnetization response and allows us to quantitatively separate surface spin disorder from intra-particle disorder contributions. Finally, we clarify the internal nanoparticle spin structure, which gives us indirect insight into the structural defect density and distribution in magnetic nanoparticles.

 

References:

[1] P. Bender et al., J. Phys. Chem. C 122, 3068 (2018).

[2] A. Lak et al., Nano Lett. 18, 6856 (2018).

[3] A. Lappas et al., Phys. Rev. X 9, 041044 (2019).

[4] S. Mühlbauer, D. Honecker, E. A. Périgo, F. Bergner, S. Disch, A. Heinemann, S. Erokhin, D. Berkov, C. Leighton, M. R. Eskildsen, A. Michels, Rev. Mod. Phys. 91, 015004 (2019).

[5] D. Zákutná et al., Phys. Rev. X 10 (3), 031019 (2020).

Speaker:
Dr. Dominika Zákutná
Charles University
Additional Authors:
  • Dr. Dirk Honecker
    ISIS Pulsed Neutron and Muon Source
  • Dr. Sabrina Disch
    University of Cologne