We have investigated self-template control of Fe3O4 thin film orientation on SrTiO3(001) substrates. The growth orientation of Fe3O4 films on SrTiO3(001) is dependent on the preparation temperature, with a crossover from the (001) to (111) grain orientation occurring at around 600 °C. In order to grow high-quality (001)-oriented Fe3O4 thin films at high temperature, a self-template technique was used, where an 8-nm-thick nucleation layer was deposited on a SrTiO3(001) substrate at 400 °C, followed by main film growth at 700 °C. This method achieved films that showed pure (001) grain orientation with bulk-like magnetic and transport behavior.
We have investigated the spontaneous polarization in Fe 3 O 4 thin films by using dynamic and static pyroelectric measurements. The magnetic and dielectric behavior of Fe 3 O 4 thin films grown on Nb:SrTiO 3 (001) substrates was consistent with bulk crystals. The well-known metal-insulator (Verwey) transition was observed at 120 K. The appearance of a pyroelectric response in the Fe 3 O 4 thin films just below the Verwey temperature shows that spontaneous polarization appeared in Fe 3 O 4 at the charge-ordering transition temperature. The polar state characteristics are consistent with bond-and site-centered charge ordering of Fe 2+ and Fe 3+ ions sharing the octahedral B sites. The pyroelectric response in Fe 3 O 4 thin films was dependent on the dielectric constant. Quasistatic pyroelectric measurement of Pd/Fe 3 O 4 /Nb:SrTiO 3 junctions showed that magnetite has a very large pyroelectric coefficient of 735 nC cm −2 K −1 at 60 K.
Temperature-driven dewetting of a self-template layer has been exploited to spontaneously grow epitaxial magnetic Fe 3 O 4 nanocrystals by pulsed laser deposition. A 10 unit cell thick Fe 3 O 4 template layer was deposited at 400 °C on a perovskite SrTiO 3 (001) substrate, followed by heating at 1100 °C, which induced dewetting of the Fe 3 O 4 template layer, forming three-dimensional islands that were uniformly distributed over the substrate surface area. These islands were used as seed crystals for the growth of spatially separated quasi-epitaxial Fe 3 O 4 nanopyramids. Structural analysis by scanning transmission electron microscopy and X-ray diffraction revealed incoherent growth of fully relaxed (001)-oriented Fe 3 O 4 nanocrystals on the SrTiO 3 (001) substrate. Higher-order epitaxial matching of the substrate and film lattices appears to be responsible for the well-defined in-plane orientation of the Fe 3 O 4 (001) nanopyramids despite the large nominal lattice mismatch of −7.5%. The nanopyramid structure strongly affected the magnetic characteristics of magnetite, dramatically reducing the coercive field compared to conventional magnetite thin films. The coercivity of the Fe 3 O 4 nanopyramids was also strongly size dependent. This is attributed to a transition between poly-and monodomain states. A superparamagnetic phase was detected for the smallest pyramid sizes.
We have investigated the effect of growth temperature on the structure, surface morphology, and magnetic properties of Fe3O4 thin films grown on SrTiO3(001) substrates by a self-template method. To eliminate the intermixing of (001) and (111) orientations that usually occurs in spinel films grown on perovskite substrates, a thin self-template layer of (001)-oriented Fe3O4 was deposited on a SrTiO3(001) substrate at 400 °C prior to the main film growth at temperatures of up to 1100 °C. Increasing the growth temperature from 400 °C to 1100 °C resulted in greatly improved crystallinity of the Fe3O4 thin films, with the rocking curve width dropping from 1.41° to 0.28°. Surface analysis by atomic force microscopy showed that raising the growth temperature increased the grain size and the surface roughness, ultimately leading to the formation of regular nanopyramid arrays at 1100 °C. The surface roughening and pyramid formation are caused by the dominance of the lowest surface energy spinel (111) crystal facet. The nanopyramids were fully relaxed but still perfectly (001)-oriented in the out-of-plane direction. The largest pyramids had the lowest coercivity due to a reduction of the demagnetization effect.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.