Molecular Beam Epitaxy of Ferrite Superlattices and Their Properties

Complex oxide superlattices are under study to develop novel magnetic magneto-optical magneto-electric functionalities using traditional ferroic materials. For these applications superlattices with highly abrupt interfaces are required. High quality epitaxial spinel ferrrite superlattices have been synthesized by oxide molecular beam epitaxy (MBE). SIMS depth profiling indicates that the superlattices have sharp interfaces, limited by instrumental broadening (Fig. 1).

The coercivity of a 7-period CoFe₂O₄/Fe₃O₄ superlattice is 200 times larger than that of the structure containing the same amount of CoFe₂O₄ and Fe₃O₄, indicating layers are strongly coupled (Fig. 2). This coupling is tentatively attributed  to an antiferromagnetic interfacial layer that magnetically couples the ferrimagnetic ferrite layers. This provides a unique route to achieving high-coercivity magnetic and magneto-optical materials for real applications.

Fig. 1 SIMS profiling of a 7 period CoFe₂O₄/MgFe₂O₄ superlattice.

Fig. 2 Hysteresis loop of a 7 period CoFe₂O₄/Fe₃O₄ superlattice.

Ji Cheng and Bruce W. Wessels