Academic Communication

Academic Report:Studying the long-range magnetic interactions between nanoparticles in hierarchical structures2019-03-12

Source: cnu       Clicks:       Size: small     middle       big

  Time: Friday, March 15, 2019, from 10:00 to 11:00 a.m.

  Location: Room 321, Third Teaching Building

  Speaker: Peter J. Klar

  Organizer: Department of Physics

  Activity/Lecturer Profile:

  Abstract:

  By combining top-down lithographic techniques with the meniscus-force deposition method, hierarchical structures consisting of defined regular elements on length scales from a few tens of nanometers to millimeters can be assembled out of magnetic nanoparticles. The long-range dipolar interaction between the nanoparticles determines the macroscopic magnetic response of the sample. Varying the size and shape of the regular elements as well as the distances between them offers the possibility to study magnetic coupling phenomena on different length scales. We study hierarchical arrangements of magnetite nanoparticles (Fe3O4) with diameters of about 20 nm by ferromagnetic resonance measurements. We demonstrate that the macroscopic properties of the structures are dominated by the assemblies of densely packed nanoparticles on the sub μm scale rather than by the interactions between these assemblies which are arranged on a grid with μm spacings or than by the macroscopic outer shape of the grid on the mm scale. The situation changes when the distances between the assemblies are reduced. We use ferromagnetic resonance (FMR) measurements to probe the magnetic interactions between the nanoparticles. Micro-magnetic simulations of the FMR spectra are carried out and allow us to relate the variation of the magnetic interactions with subtle lineshape changes of the spectra.