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Appl. Phys. Lett. 103, 132909 (2013).
Z. Wang, Y. Wang, W. Ge, J. Li ,D. Viehland.
Department of Materials Science and Engineering, Virginia Tech, Blacksburg, Virginia 24061, USA.
Abstract
We explored the relationship between phase transformation and magnetoelectric effect by depositing epitaxial CoFe2O4 films on ⟨110⟩ oriented Pb(Mg,Nb)O3-PbTiO3 (PMN-PT) with three different PbTiO3 contents (PMN-28PT, PMN-29.5PT, and PMN-30PT). Electric-field controlled rhombohedral to orthorhombic phase transformation was confirmed by bothpiezoelectric and dielectric constant measurements. A giant in-plane (IP) uniaxial strain in CoFe2O4 film was induced due to dramatic lattice parameter change trigged by phase transition. Magnetic easy axis can be rotated from IP⟨110⟩ to IP⟨001⟩. More importantly, thephase transformation could be either reversible or irreversible, resulting in either volatile or nonvolatile magnetic easy axis rotations.
Additional information:
In this work, we tried to build a relationship between the ferroelectric phase transition and the magnetoelectric effect which is realized though interface elastic strain coupling between ferroelectric and ferromagnetic components.
PMN-PT shows giant electromechanical coupling due to the electric field modulation of ferroelectric polarizations. Polarization can be rotated or reorientated by the external electric field and thus induce a strain during this process. The strain can be volatile or nonvolatile based on the stability of the electric field induced polarization state in the ferroelectric single crystals.
On the other hand, Mn doped CoFe2O4 (MCFO) has the largest magnetostriction among all the ferrites. More fortunately, we can grown epitaxial MCFO on single crystal PMN-PT single crystals, which guarantees a perfect interface elastic strain transferring.
By varying the composition of the PMN-PT substrates, we can get both volatile and nonvolatile modulated magnetic states in the MCFO/PMN-PT monolithic magnetoelectric heterostructure. This promises application potentials in magnetic memory and microwave devices.
In the picture, we show the coexistence of magnetic shape and strain anisotropy for MCFO thin film on PMN-PT. The change in the magnetization squareness (Mr/Ms) is due to the electric field controlled strain anisotropy. The magnetic shape anisotropy is constant during our measurement, but it can be easily controlled by patterning of the magnetic film for some special applications.
