Strongly exchange coupled inverse ferrimagnetic soft/hard, Mn_xFe_(3-x)O4/Fe_xMn_(3-x)O4, core/shell heterosrructured nanoparticles

摘要

Inverted soft/hard, in contrast to conventional hard/soft, bi-magnetic core/shell nanoparticles of Mn_xFe_(3-x)O4/Fe_xMn_(3-x)O4 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.