Spin-Polarized Flexoelectricity

Flexoelectricity describes the coupling between electric polarization and a strain gradient. Because it is represented by an even parity rank-4 tensor, it is not prohibited by the presence of inversion symmetry in a crystal in the same way as piezoelectricity. First-principles methods for calculating flexoelectric tensor components have been developed that involve calculating electronic and lattice contributions using various charge-moment and force tensors.¹ In magnetic materials, these charge moments can be spin-polarized – that is, the densities of spin up and down electrons can respond differently to atomic displacement. Based on this principle, we developed a method for calculating spin-polarized flexoelectric tensor components. The existence of spin-polarization in the flexoelectric tensor could be used to create spin-polarized channels of surface charge. We apply our technique to several rock-salt materials with various magnetic orderings to calculate spin-polarized flexoelectric tensor components. We outline a method for experimental confirmation of our work by calculating effective spin-polarized flexoelectric coefficients for particular cases of beam-bending. This work predicts a novel method for developing spin-channels which may be of use in spintronics.<br/>Acknowledgements: This work was sponsored in part by the National Science Foundation through CBET-1729787 and by the Department of Navy, Office of Naval Research, under ONR Award number N00014-16-1-2280. The US Government has a royalty-free license throughout the world on all copyrightable material contained herein.<br/>1. Hong, J. and D. Vanderbilt, <i>First-principles theory and calculation of flexoelectricity.</i> Physical Review B, 2013. <b>88</b>(17): p. 174107.