Structure-Property Relationship of CoFe2O4 Thin Films
Structure-Property Relationship of CoFe2O4
tunnel junctions consisting of a ferroelectric tunnel barrier
between two ferromagnetic electrodes, have aroused intense interest
the interactions between the ferroelectric and ferromagnetic layers
lead to new spin-dependent electron tunneling phenomena. In order to couple the
properties across the
interfaces, high quality epitaxial growth is required, while
maintaining good magnetotransport behavior.
We are addressing this by using metalorganic chemical
(MOCVD) to grow suitable heterostructures, and using TEM and AFM to
have grown CoFe2O4 (CFO)
thin films epitaxially on (001)
SrTiO3 despite the large lattice mismatch. Electron diffraction
patterns and HREM images
confirm that the epitaxial relationship is CFO(004)//STO(002)
and CFO<100>//STO<100>. The magnetic anisotropy
measured in the CFO
thin films can thus be ascribed to lattice strain.
The TEM bright field images and AFM
topography images show that the CFO films deposited at high temperature
(>600°C) have very rough surfaces (~22 nm) and a columnar
resulting from an island growth mode (generally observed in MOCVD
for CFO films grown at lower
temperature (400-600°C), we observed that the surface roughness drops
orders of magnitude to 0.2 nm. This
suggests a change to a layer-by-layer growth mode, which occurs because
lower substrate temperature does not provide enough energy for the
to congregate to form large islands.
magnetic properties are relatively independent of deposition
although a rougher surface can result in pinning sites during the
have shown that we can use MOCVD to grow epitaxial CFO thin films, and
can control surface roughness without degrading magnetic properties
over a wide
range of deposition temperatures.
deposition temperature window will enable further development of
systems in the future, and also makes this potentially an
and economical deposition technique.
the future, we will focus on fabricating multiferroic heterostructures
as the ferromagnetic material and correlating the
properties with microstructure.