Abstract
Multiferroic composites of ferromagnetic and ferroelectric phases are of importance for studies on mechanical strain mediated coupling between the magnetic and electric subsystems. This work is on DNA-assisted self-assembly of superstructures of such composites with nanometer periodicity. The synthesis involved oligomeric DNA-functionalized ferroelectric and ferromagnetic nanoparticles, 600 nm BaTiO3 (BTO) and 200 nm NiFe2O4 (NFO), respectively. Mixing BTO and NFO particles, possessing complementary DNA sequences, resulted in the formation of ordered core-shell heteronanocomposites held together by DNA hybridization. The composites were imaged by scanning electron microscopy and scanning microwave microscopy. The presence of heteroassemblies along with core-shell architecture is clearly observed. The reversible nature of the DNA hybridization allows for restructuring the composites into mm-long linear chains and 2D-arrays in the presence of a static magnetic field and ring-like structures in a rotating-magnetic field. Strong magneto-electric (ME) coupling in as-assembled composites is evident from static magnetic field H induced polarization and low-frequency magnetoelectric voltage coefficient measurements. Upon annealing the nanocomposites at high temperatures, evidence for the formation of bulk composites with excellent cross-coupling between the electric and magnetic subsystems is obtained by H-induced polarization and low-frequency ME voltage coefficient. The ME coupling strength in the self-assembled composites is measured to be much stronger than in bulk composites with randomly distributed NFO and BTO prepared by direct mixing and sintering.
Highlights
INTRODUCTIONStudies so far on nanocomposites have primarily focused on thin films and nanopillars in which substrate clamping weakens the strength of ME coupling.[47,48,49] Such clamping effects are expected to be absent in nanostructures of core-shell particles, and coaxial tubes and wires.[51,52,53,54] In a recent study 12-200 nm particles of barium titanate (BTO) and cobalt ferrite were functionalized by attaching carboxylate and amine groups, respectively, and a core-shell particulate composite was formed by covalent bonds between the two particles with the addition of a coupling agent.[54] In our recent work on chemical self-assembly we utilized the (CuAAC) “click” reaction to synthesize heteronanocomposites by functionalizing BTO and nickel ferrite NiFe2O4 (NFO) with complementary azide and alkyne reaction groups.[55,56,57,58,59] The assembled composite showed evidence for strong ME coupling.[57,58,59] But these efforts clearly indicated the strengths and weaknesses of pure chemical assembly
Manipulation of materials at the nanoscale has recently become an area of great interest to the materials science community.[1]
The reversible nature of the DNA hybridization allows for restructuring the composites into mm-long linear chains and 2D-arrays in the presence of a static magnetic field and ring-like structures in a rotating-magnetic field
Summary
Studies so far on nanocomposites have primarily focused on thin films and nanopillars in which substrate clamping weakens the strength of ME coupling.[47,48,49] Such clamping effects are expected to be absent in nanostructures of core-shell particles, and coaxial tubes and wires.[51,52,53,54] In a recent study 12-200 nm particles of barium titanate (BTO) and cobalt ferrite were functionalized by attaching carboxylate and amine groups, respectively, and a core-shell particulate composite was formed by covalent bonds between the two particles with the addition of a coupling agent.[54] In our recent work on chemical self-assembly we utilized the (CuAAC) “click” reaction to synthesize heteronanocomposites by functionalizing BTO and nickel ferrite NiFe2O4 (NFO) with complementary azide and alkyne reaction groups.[55,56,57,58,59] The assembled composite showed evidence for strong ME coupling.[57,58,59] But these efforts clearly indicated the strengths and weaknesses of pure chemical assembly. Characterization by several microscopy techniques and studies on ME coupling are provided in the sections that follow
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
