Ferrotoroidic structures: polar flux-closure, vortices and skyrmions

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The impressive amount of data produced daily by modern society requires more efficient information storage. Current capabilities need not only to be increased to meet demand, but also to be fundamentally changed to offer better density, power consumption, access speed and time stability. Existing data encoding is based on switching of ferroic order parameters such as magnetisation and polarisation that exist in ferromagnetic and ferroelectric materials, respectively. The effect of finite size sets a fundamental limit of the data density and retention that is being rapidly approached by current technologies. Therefore, there is critical need for novel data encoding mechanisms. One alternative is offered by ferrotoroidic structures that show multiple order parameters, related to properties such as chirality and winding number, which can be used to encode extra information. Not only do these additional parameters multiply the achievable information density, but they are predicted to exist exactly at the characteristic length where classical ferroic parameters are no longer effective for data encoding. Thus, ferrotoroidics provide an alternative way to overcome the limits of classical data storage. Ferrotoroidic structures have been theoretically predicted but only very recently have they been experimentally observed. Besides the enormous application potential, especially in non-volatile memories, these exotic polar entities may require new physics to be fully understood. The present research aims to experimentally elucidate the origin of the ferrotoroidic structures through a comprehensive program of work. By understanding this complex phenomena, we will gain control of and tune the ferrotoroidicity in terms of density, chirality and spatial positioning. We are especially targeting oxide polar ferrotoroidics in which the reorientation of the spontaneous polarization is a result of atomic displacement. For this reason, transmission electron microscopy is the technique of choice to determine the oxide properties at nanoscopic scale by measuring the displacement of atoms relative to each other. In-situ electron microscopy will provide real time information to investigate the effective interactions between electric fields and polar entities as well as potentially switch the toroidal moment chirality to demonstrate data encoding.