MSE Seminar Series: Dwight Viehland

Friday, April 1, 2016
1:00 p.m.-2:00 p.m.
Room 2110, Chemical and Nuclear Engineering Building
JoAnne Kagle

Dwight Viehland
Jack E. Cowling Professor, Materials Science and Engineering
Virginia Tech

Mesoscale Interfacial Dynamics in Magnetoelectric Nanocomposites

Both heterostructural and vertically integrated two phase ME epitaxial thin layers have been fabricated by various deposition methods. With regards to vertically integrated nanostructures, our investigations have shown various phase architectures of self-assembled BiFeO3-CoFe2O4 (BFO-CFO) thin films on differently oriented SrTiO3 (STO) and Pb(Mg1/3Nb2/3)O3-xat%PbTiO3 (PMN-x%PT) substrates [40]. CFO forms segregated square, stripe, and triangular nanopillars embedded in a coherent BFO matrix on (001)-, (110)- and (111)-oriented substrates, respectively. Nanostructures with an aspect ratio of up to 5:1 with a prominent magnetic anisotropy were obtained on both (001) and (110) substrates along out-of-plane and in-plane directions. Magnetic easy axis rotation from in-plane to out-of-plane directions was realized through aspect ratio control. These studies established a detailed relationship of magnetic anisotropy with specific shapes and dimensions of ordered magnetic arrays. The results suggest a way to effectively control the magnetic anisotropy in patterned ferromagnetic oxide arrays with tunable shape, aspect ratio, and elastic strain conditions of the nanostructures. Using an epitaxial engineering approach, many different types of nanostructures are seemingly possible. It offers the ability to change the balance of terms in the free energy by which to tune the magnetic anisotropy via shape, and also as we will show by electric field.

These two phase layers, and of CFO heterostructures, on PMN-x%PT have pronounced magnetoelectric effects. In particular, large E-field tunable magnetic anisotropies were found. For PMN-x%PT substrate compositions near a morphotropic phase boundary (MPB), both volatile and non-volatile effects have been reported, which can be tuned with substrate composition. This opens up the unique possibility to develop giant ME materials with unique multi-state reconfigurable properties, with and without memory.

Audience: Public 

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