(533d) 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.