Regensburg 2016 – scientific programme
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MA: Fachverband Magnetismus
MA 39: Magnetic Particles
MA 39.7: Talk
Thursday, March 10, 2016, 11:15–11:30, H31
Experimental investigation of the spin structure in MnO nanoparticles, powder and single crystal — •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 at Heinz Maier-Leibnitz Zentrum MLZ, Forschungszentrum Jülich GmbH, Garching — 3Institut für Anorganische und Analytische Chemie, Johannes Gutenberg-Universität Mainz, Mainz
We have studied the magnetic spin structure of antiferromagnetic (AF) MnO nanoparticles (NPs), powder and single crystal using both magnetometry and polarized neutron scattering. MnO NPs show a peculiar peak at low temperatures (ca. 25K) instead at the Néel temperature of 120K in the magnetization curves. However, polarized neutron scattering results show the expected behavior of the AF order parameter of MnO. For MnO powder and single crystal, features at both the low temperature and Néel temperature have been found in magnetometry. A phase transition at the peak temperature in the MnO single crystal has been observed in neutron scattering. This peak temperature matches the Tc of Mn2O3 or Mn3O4. 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 Mn2O3 or Mn3O4 shell.