000200791 001__ 200791 000200791 005__ 20240619091948.0 000200791 0247_ $$2doi$$a10.1103/PhysRevB.91.094421 000200791 0247_ $$2Handle$$a2128/8613 000200791 0247_ $$2WOS$$aWOS:000351426000001 000200791 037__ $$aFZJ-2015-03186 000200791 082__ $$a530 000200791 1001_ $$0P:(DE-HGF)0$$aLefmann, K.$$b0$$eCorresponding Author 000200791 245__ $$aDynamic rotor mode in antiferromagnetic nanopartciles 000200791 260__ $$aCollege Park, Md.$$bAPS$$c2015 000200791 3367_ $$0PUB:(DE-HGF)16$$2PUB:(DE-HGF)$$aJournal Article$$bjournal$$mjournal$$s1431956687_3907 000200791 3367_ $$2DataCite$$aOutput Types/Journal article 000200791 3367_ $$00$$2EndNote$$aJournal Article 000200791 3367_ $$2BibTeX$$aARTICLE 000200791 3367_ $$2ORCID$$aJOURNAL_ARTICLE 000200791 3367_ $$2DRIVER$$aarticle 000200791 520__ $$aWe present experimental, numerical, and theoretical evidence for an unusual mode of antiferromagnetic dynamics in nanoparticles. Elastic neutron scattering experiments on 8-nm particles of hematite display a loss of diffraction intensity with temperature, the intensity vanishing around 150 K. However, the signal from inelastic neutron scattering remains above that temperature, indicating a magnetic system in constant motion. In addition, the precession frequency of the inelastic magnetic signal shows an increase above 100 K. Numerical Langevin simulations of spin dynamics reproduce all measured neutron data and reveal that thermally activated spin canting gives rise to an unusual type of coherent magnetic precession mode. This “rotor” mode can be seen as a high-temperature version of superparamagnetism and is driven by exchange interactions between the two magnetic sublattices. The frequency of the rotor mode behaves in fair agreement with a simple analytical model, based on a high-temperature approximation of the generally accepted Hamiltonian of the system. The extracted model parameters, such as the magnetic interaction and the axial anisotropy, are in excellent agreement with results from Mössbauer spectroscopy. 000200791 536__ $$0G:(DE-HGF)POF3-551$$a551 - Functional Macromolecules and Complexes (POF3-551)$$cPOF3-551$$fPOF III$$x0 000200791 536__ $$0G:(DE-HGF)POF3-6G4$$a6G4 - Jülich Centre for Neutron Research (JCNS) (POF3-623)$$cPOF3-623$$fPOF III$$x1 000200791 536__ $$0G:(DE-HGF)POF3-6215$$a6215 - Soft Matter, Health and Life Sciences (POF3-621)$$cPOF3-621$$fPOF III$$x2 000200791 542__ $$2Crossref$$i2015-03-19$$uhttp://link.aps.org/licenses/aps-default-license 000200791 7001_ $$0P:(DE-HGF)0$$aJacobsen, H.$$b1 000200791 7001_ $$0P:(DE-HGF)0$$aGarde, J.$$b2 000200791 7001_ $$0P:(DE-HGF)0$$aHedegard, P.$$b3 000200791 7001_ $$0P:(DE-Juel1)131040$$aWischnewski, Andreas$$b4$$ufzj 000200791 7001_ $$0P:(DE-HGF)0$$aAncona, S. N.$$b5 000200791 7001_ $$0P:(DE-HGF)0$$aJacobsen, H. S.$$b6 000200791 7001_ $$0P:(DE-HGF)0$$aBahl, C. R. 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