Abstract
Large changes in the magnetization of ferromagnetic films can be electrically driven by non-180° ferroelectric domain switching in underlying substrates, but the shear components of the strains that mediate these magnetoelectric effects have not been considered so far. Here we reveal the presence of these shear strains in a polycrystalline film of Ni on a 0.68Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 substrate in the pseudo-cubic (011)pc orientation. Although vibrating sample magnetometry records giant magnetoelectric effects that are consistent with the hitherto expected 90° rotations of a global magnetic easy axis, high-resolution vector maps of magnetization (constructed from photoemission electron microscopy data, with contrast from X-ray magnetic circular dichroism) reveal that the local magnetization typically rotates through smaller angles of 62-84°. This shortfall with respect to 90° is a consequence of the shear strain associated with ferroelectric domain switching. The non-orthogonality represents both a challenge and an opportunity for the development and miniaturization of magnetoelectric devices.
Highlights
For ME heterostructures based on PMN-PT, whose polarization lies locally along a pseudocubic pc direction, early studies[22] tended to exploit the (001)pc orientation
Given that XMCD-PEEM images of a single magnetization component have likewise been used to infer that the local magnetization undergoes electrically driven rotations of 90, no discrepancy between macroscopic and microscopic ME effects has been hitherto identified in the literature, implying that device performance would not be modified by the miniaturization required for data-storage applications[40,41,42] (PEEM is photoemission electron microscopy, XMCD is x-ray magnetic circular dichroism)
Our analysis reveals that this shortfall arose because the ferroelectric domain switching was accompanied by shear strains, whose magnitude we identify from the PMN-PT unit cell given in ref
Summary
For ME heterostructures based on PMN-PT, whose polarization lies locally along a pseudocubic pc direction, early studies[22] tended to exploit the (001)pc orientation. We report global and local ME effects in a 10 nm-thick polycrystalline film of Ni on a substrate of PMN-PT (x = 0.32) (011)pc, whose ferroelectric domains possessed out-of-plane components of polarization that were electrically switched on and off.
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