Nanoscale, 2012,4, 5138-5147
Marta Estrader , Alberto López-Ortega , German Salazar-Alvarez, Igor Golosovsky , Marianna Vasilakaki , Kalliopi Trohidou , David Keavney , Randy Dumas , Jordi Sort , Sonia Estrade , Dolors Baro , Santiago Suriñach , Francesca Peiro and Josep Nogués
Inverted soft|hard, in contrast to conventional hard|soft, bi-magnetic core|shell nanoparticles of MnxFe3-xO4|FexMn3-xO4 with two different core sizes (7.5 and 11.5 nm) and fixed shell thickness (~ 0.6 nm) have been synthesized. The structural characterization suggests that the particles have an interface with a graded composition. The magnetic characterization confirms the inverted soft|hard structure and evidences a strong exchange coupling between the core and the shell. Moreover, larger soft core sizes exhibit smaller coercivities and loop shifts, but larger blocking temperatures, as expected from spring-magnet or graded anisotropy structures. The results indicate that, similar to thin film systems, the magnetic properties of soft|hard core|shell nanoparticles can be fine tuned to match specific applications.
