Static and Dynamic Magnetic Properties of Composite Au-Fe$_{3}$O $_4$Nanoparticles

Fe
₃
O
₄
(9 nm) grown epitaxially on one or several facets of a seed Au particle (8 nm) leads to two distinct composite nanoparticle structures dubbed "dumbbell-" and "flower-like." These particles exhibit novel magnetic behavior such as large magnetic anisotropy compared to the single component Fe
₃
O
₄
. We have studied the static and dynamic magnetic properties using temperature and field-dependent dc magnetization and RF transverse susceptibility. While the magnetic properties of dumbbell-like particles are relatively conventional, field-cooled M-H loops of flower-shaped particles as well as the transverse susceptibility show large shifts along the field axis indicative of exchange bias