Size dependent magnetic properties of bi-magnetic "core-shell" passivated MnO nanoparticles

ALBERTO LÓPEZ-ORTEGA; MARTA ESTRADER; DINA TOBIA; ELIN WINKLER; GERMAN SALAZAR-ALVAREZ; IGOR GOLOSOVSKY; JORDI SORT; SANTIAGO SURIÑACH; ROBERTO ZYSLER; MARÍA DOLORS BARÓ; JOSEP NOGUÉS

Karlsruhe, Alemania

Conferencia; International Conference on Magnetism; 2009

The study of bi-magnetic core-shell nanoparticles with double-inverted antiferromagnetic(AFM)-core/ferrimagnetic(FiM)-shell structure with TC < TN (TC and TN, Curie and Néel temperatures, respectively) is presented, as opposed to the typical FM-core/AFM-shell with TC > TN. The nanoparticles are synthesized by thermolysis of metal organic salt leading to the AFM-core (MnO) which is passivated under air yielding to the FiM- shell (gamma-Mn2O3 or Mn3O4). Different core sizes from 2 to 20 nm with a roughly constant shell of 2-3 nm have been analyzed through different methods such as TEM, X-ray andneutron diffraction, magnetization, ac-susceptibility and ESR. These samples show a range of novel magnetic properties such as size dependent passivation shell, non-monotonic dependence of exchange bias and coercitivity with the AFM-core size, enhanced core TN, induced moments above TC of the shell due to the coupling to the core (i.e. a magnetic proximity effect).