Correlating material-specific layers and magnetic distributions within onion-like Fe3O4/MnO/γ-Mn2O3 core/shell nanoparticles

J. Appl. Phys. 113, 17B531 (2013)

K. L. Krycka; J. A. Borchers; M. Laver; G. Salazar-Alvarez; A. López-Ortega; M. Estrader; S. Suriñach; M. D. Baró; J. Sort; J. Nogués

DOI: 10.1063/1.4801423

Abstract
The magnetic responses of two nanoparticle systems comprised of Fe₃O₄/γ-Mn₂O₃ (soft ferrimagnetic, FM/hard FM) and Fe₃O₄/MnO/γ-Mn₂O₃ (soft FM/antiferromagnetic, AFM/hard FM) are compared, where the MnO serves to physically decouple the FM layers. Variation in the temperature and applied field allows for Small Angle Neutron Scattering (SANS) measurements of the magnetic moments both parallel and perpendicular to an applied field. Data for the bilayer particle indicate that the graded ferrimagnetic layers are coupled and respond to the field as a single unit. For the trilayer nanoparticles, magnetometry suggests a Curie temperature (T_C) ≈ 40 K for the outer γ-Mn₂O₃component, yet SANS reveals an increase in the magnetization associated with outer layer that is perpendicular to the applied field above T_C during magnetic reversal. This result suggests that the γ-Mn₂O₃ magnetically reorients relative to the applied field as the temperature is increased above 40 K.