Phase Formation and Exchange Bias in LuFeO₃–Co_xFe_3–xO₄ Nanocomposite Films

Abstract

Vertically aligned nanocomposite thin films comprising antiferromagnetic and ferroelectric LuFeO 3 and ferrimagnetic Co x Fe 3−x O 4 are synthesized by a codeposition method using pulsed laser deposition from two or three targets of different composition. The phases that form (perovskite, spinel, and rocksalt), their compositions, and the magnetic anisotropy of the nanocomposites are strongly influenced by the selection of targets from the group of Lu-rich LuFeO 3 , Fe-rich LuFeO 3 , CoFe 2 O 4 , and Co 3 O 4 . When the Co and Fe are delivered from different targets, the spinel crystals have a range of compositions. Owing to the crystallographic relationship between the perovskite LuFeO 3 and spinel Co x Fe 3−x O 4 in the nanocomposites, a negative exchange bias of −5.3 mT at room temperature is demonstrated upon field cooling a 31 nm thick LuFeO 3 −Co 1.2 Fe 1.8 O 4 film.