Low Pressure Metalorganic Chemical Vapor Deposition of Nickel Ferrite Thin Films On Ferroelectric Substrates

Multiferroic magnetoelectric (ME) materials have been the focus of active research in the recent years. Although some single-phase materials exhibit ME effect, these suffer from problems such as current leakages, weak ME coupling and low ordering temperatures. Furthermore, since most of these compounds have definite compositions, the possibility of optimization of magnetoelectric property through ion substitution or doping is very limited.  However, heterostructures such as bilayered / multilayered thin films, nanopillars and nanowires are more promising for the future on-chip integration applications since the coupling in such structures is many orders of magnitude stronger. One of the most promising approaches is to synthesize composites of magnetostrictive and piezoelectric materials. In such composites the mechanical strain between the two materials is employed to induce the magnetoelectric effect. However, the ME effect in this case may be non-linear unlike in the case of single-phase materials. Also, the interfacial mechanical strain should be transferred between the components with minimal losses.

Our work focuses on the fabrication of bilayered/multilayered heterostructures of magnetostrictive NiFe₂O₄ (NFO) and piezoelectric materials. NFO is a promising magnetic phase for ME heterostructures due to its low anisotropy, high permeability with high resistivity, low eddy current losses and smaller coercive field. The ferromagnetic NFO thin films were deposited using low-pressure metalorganic chemical vapor deposition (MOCVD) method as it is a suitable technique preferred for production by industry due to its advantages such as large conformal coverage, stoichiometric control and high yield. N-butylferrocene and nickelocene were used as precursors. The films were deposited on piezoelectric lead-zironium titanate substrates at pressure of 10-20 Torr and temperature of 350-500 ºC. The heterostructures were characterized for composition, structure, morphology and magnetoelectric effect.