Regensburg 2007 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 15: Poster:ThinFilms(1-33),Transp.(34-49),ExchBias(50-56),
Spindynamics(57-70),Micro-nanostr.Mat.(71-82),
Particles/Clust.(83-88), Mag.Imag./Surface(89-96),
Spinelectronics(97-109), Theory/Micromag.(110-116),
Spinstruct/Phasetr.(117-128),Magn.Mat.(129-139),
Aniso.+Measuring(140-145), MolMag.(146-152),
MSMA(153-156)
MA 15.83: Poster
Dienstag, 27. März 2007, 15:00–19:00, Poster A
Magnetism in confined geometry: Magnetic critical scattering of MnO nanoparticles — •Mikhail Feygenson1, Werner Schweika1, Serguei Vakhrushev2, Alexander Ioffe1, and Thomas Brückel1 — 1Institut für Festkörperforschung, Forschungszentrum Jülich GmbH, D-52425 Jülich — 2A. F. Ioffe Physico-Technical Institute, 194021, St. Petersburg, Russia
We studied the magnetic order and phase transition of MnO embedded in a porous glass by polarized neutron scattering using the DNS-instrument at the research center in Jülich. The nanopores filled with MnO are wormlike structures with a typical diameter of 70 Å. From the temperature dependence of the magnetic (1/2 1/2 1/2) Bragg intensity we obtained that for the MnO nanoparticles the phase transition is continuous with a Néel temperature TN=122K. This is in contrast to bulk MnO, which exhibits a first order phase transition at 118K. Furthermore, we observed that a part of the MnO nanoparticle material remains disordered even at 2K, which indicates frustration at the interface MnO to glass. We interpret the higher TN to be due to strain on MnO embedded in nanopores. The change in TN can be related to an effective pressure of 23 GPa according to the (p,T)-phasediagram of bulk MnO [1]. The continuous character of the transition and the unusual temperature dependence with a reduced order parameter can be described and modeled by surface induced disorder [2,3].
[1] C.S.Yoo et. al., PRL 94 115502 (2005) [2] R.Lipowsky, Ferroelectrics 73(1987) [3] W.Schweika et. al., PRB 53, 8937 (1996)