Berlin 2015 – scientific programme
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MA: Fachverband Magnetismus
MA 38: Magnetic Nanoparticles
MA 38.2: Talk
Thursday, March 19, 2015, 09:45–10:00, H 0110
Experimental investigation and modeling of the spin structure in MnO nanoparticles — •Xiao Sun1, Alice Klapper1, Yixi Su2, Kirill Nemkovski2, Oskar Köhler3, Heiko Bauer3, Anna Schilmann3, Wolfgang Tremel3, Oleg Petracic1, and Thomas Brückel1 — 1Jülich Centre for Neutron Science JCNS and Peter Grünberg Institut PGI, JARA-FIT, Forschungszentrum Jülich GmbH, Jülich — 2Jülich Centre for Neutron Science JCNS, Forschungszentrum Jülich GmbH, Outstation at MLZ, Garching — 3Institut für Anorganische und Analytische Chemie, Johannes Gutenberg-Universität Mainz, Mainz
The spin structure of antiferromagnetic (AF) MnO nanoparticles (NPs) has been investigated for various NP diameters (5-20nm) using both magnetometry and polarized neutron scattering. Magnetization curves show a peculiar peak at low temperatures (ca. 25K) instead at the Néel temperature of 120K. However, the AF order parameter of MnO shows the expected behavior from polarized neutron scattering studies. In MnO powder, features at both the low temperature (ca. 25K) and the Néel temperature can be found. To understand the observed behavior further magnetometry studies using hysteresis curves, memory effect and susceptibility measurements were employed. We conclude that the magnetic behavior of MnO NPs can be explained by a superposition of superparamagnetic-like thermal fluctuations of the AF Néel vector inside an AF core and a strong magnetic coupling to a FM shell. Moreover, we employed Monte-Carlo simulations of the spin structure to model the observed behavior.