Anisotropic Fe3O4/Mn3O4 Hybrid Nanocrystals with Unique Magnetic Properties

This work explores novel nanomagnets by site- and facet-selective epitaxy of Mn3O4 nanodomains onto colloidal Fe3O4 nanoprisms in solution. At 190 C, the Mn3O4 nanodomains epitaxially grow at three vertexes of the Fe3O4 nanoprisms in solution and form horns-on-prism hybrid nanocrystals. At 240 C and in the same reaction solution, the epitaxy occurs on the top facet of the Fe3O4 nanoprisms, which results in prism-on-prism hybrid nanocrystals. As the temperature increases from 190 to 240 C, the ratio between the prism-on-prism and horns-on-prism nanocrystals increases. A possible formation mechanism of Fe3O4/Mn3O4 hybrid nanocrystals is proposed. Novel magnetic behaviors, such as compensation point, large positive (or negative) exchange bias, and unusual hysteresis loop character (constricted at low field and expanded at high field), have been observed for both types of anisotropic hybrid nanomagnets. These unique magnetic properties are consistent with controlled switch of relative magnetization orientations between Fe3O4 and Mn3O4 nanodomains from parallel to antiparallel exchange-coupled configurations.