TY - JOUR A1 - Bender, P. A1 - Bogart, L.K. A1 - Posth, O. A1 - Szczerba, Wojciech A1 - Rogers, S.E. A1 - Castro, A. A1 - Nilsson, L. A1 - Zeng, L. J. A1 - Sugunan, A. A1 - Sommertune, J. A1 - Fornara, A. A1 - Gonzales-Alonso, D. A1 - Fernandez Barquin, L. A1 - Johansson, C. T1 - Structural and magnetic properties of multi-core nanoparticles analysed using a generalised numerical inversion method N2 - The structural and magnetic properties of magnetic multi-core particles were determined by numerical inversion of small angle scattering and isothermal magnetisation data. The investigated particles consist of iron oxide nanoparticle cores (9 nm) embedded in poly(styrene) spheres (160 nm). A thorough physical characterisation of the particles included transmission electron microscopy, X-ray diffraction and asymmetrical flow field-flow fractionation. Their structure was ultimately disclosed by an indirect Fourier transform of static light scattering, small angle X-ray scattering and small angle neutron scattering data of the colloidal dispersion. The extracted pair distance distribution functions clearly indicated that the cores were mostly accumulated in the outer surface layers of the poly(styrene) spheres. To investigate the magnetic properties, the isothermal magnetisation curves of the multi-core particles (immobilised and dispersed in water) were analysed. The study stands out by applying the same numerical approach to extract the apparent moment distributions of the particles as for the indirect Fourier transform. It could be shown that the main peak of the apparent moment distributions correlated to the expected intrinsic moment distribution of the cores. Additional peaks were observed which signaled deviations of the isothermal magnetisation behavior from the non-interacting case, indicating weak dipolar interactions. KW - Numerical inversion KW - Magnetic nanoparticles KW - Iron oxides KW - Magnetic properties KW - Structural properties PY - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-400952 SN - 2045-2322 VL - 7 SP - Article 45990, 1 EP - 14 AN - OPUS4-40095 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bender, P A1 - Balceris, C. A1 - Ludwig, F A1 - Posth, O A1 - Bogart, L. K. A1 - Szczerba, Wojciech A1 - Castro, A A1 - Nilsson, L A1 - Costo, R A1 - Gavilan, H A1 - Gonzalez-Alonso, D A1 - de Pedro, I A1 - Barquin, L. F. A1 - Johansson, C T1 - Distribution functions of magnetic nanoparticles determined by a numerical inversion method N2 - In the present study, we applied a regularized inversion method to extract the particle size, magnetic moment and relaxation-time distribution of magnetic nanoparticles from small-angle x-ray scattering (SAXS), DC magnetization (DCM) and AC susceptibility (ACS) measurements. For the measurements the particles were colloidally dispersed in water. At first approximation the particles could be assumed to be spherically shaped and homogeneously magnetized single-domain particles. As model functions for the inversion, we used the particle form factor of a sphere (SAXS), the Langevin function (DCM) and the Debye model (ACS). The extracted distributions exhibited features/peaks that could be distinctly attributed to the individually dispersed and non-interacting nanoparticles. Further analysis of these peaks enabled, in combination with a prior characterization of the particle ensemble by electron microscopy and dynamic light scattering, a detailed structural and magnetic characterization of the particles. Additionally, all three extracted distributions featured peaks, which indicated deviations of the scattering (SAXS), magnetization (DCM) or relaxation (ACS) behavior from the one expected for individually dispersed, homogeneously magnetized nanoparticles. These deviations could be mainly attributed to partial agglomeration (SAXS, DCM, ACS), uncorrelated surface spins (DCM) and/or intra-well relaxation processes (ACS). The main advantage of the numerical inversion method is that no ad hoc assumptions regarding the line shape of the extracted distribution functions are required, which enabled the detection of these contributions. We highlighted this by comparing the results with the results obtained by standard model fits, where the functional form of the distributions was a priori assumed to be log-normal shaped. KW - SAXS KW - Small-angle X-ray scattering KW - Nanoparticle PY - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-429373 SN - 1367-2630 VL - 19 SP - 073012, 1 EP - 073012, 19 PB - IOP Publ. Ltd. AN - OPUS4-42937 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -