Flexoelectric nanodomains in rare-earth iron garnet thin films under strain gradient

Flexoelectricity is a universal property associated with dielectric materials, wherein they exhibit remanent polarization induced by strain gradient. Rare-earth iron garnets, R3Fe5O12, are ferrimagnetic insulators with useful magnetic properties. However, they are unlikely to show remanent dielectric polarization because of their centrosymmetric structure. Here, to induce flexoelectricity, we investigate various rare-earth iron-garnet thin films deposited on lattice-mismatched substrates. Atomic-resolution scanning transmission electron microscopy demonstrates the presence of 15 nm-thick strain gradients in Sm3Fe5O12 films between epitaxially strained tetragonal and relaxed cubic structures. Furthermore, negatively polarized nanodomains are imaged by scanning nonlinear dielectric microscopy. It suggests a generation of flexoelectricity, where the polarization points down toward the substrate in the out-of-plane direction. X-ray magnetic circular dichroism demonstrates hysteresis with a large coercive field originating from the strain-gradient layer. We believe that our study will pave the way for achieving dielectric polarization even in nonpolar centrosymmetric materials by strain-gradient engineering.

Hydrothermal Synthesis of Various Magnetic Properties of Controlled Micro/Nanostructured Powders and Films of Rare-Earth Iron Garnet

In this study, the synthesis and magnetic properties of the rare-earth iron garnets Sm3Fe5O12, Pr3Fe5O12, and Er3Fe5O12 (in the form of powders and thin films) are reported. According to the composition, shape, and size of particles, the optimal precipitant for the synthesis of Sm3Fe5O12, Pr3Fe5O12, and Er3Fe5O12 films is an aqueous solution. The parameters for the synthesis of powders and films of the rare-earth iron garnets with micro- and nano-particles have been investigated and selected. The magnetic properties of these materials were studied; field dependencies of the magnetic moment (hysteresis loops) of nanostructured powders of iron garnets of samarium, praseodymium, and erbium in the range of +20 kOe to −20 kOe were obtained. The structural features of the Al2O3 substrate on which the films were formed are also shown.