Ferrotoroidic structures: polar flux-closure, vortices and skyrmions

Lead Research Organisation: University of Warwick
Department Name: Physics

Abstract

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.

Planned Impact

Ferrotoroidic structures have become a very hot topic of research, having potential technological applications whilst also challenging fundamental theories. We expect to achieve an immediate impact by publishing our results in high impact broad interest and focused reviewed journals. The interplay between structure, strain, electric and magnetic field results in novel ferroic materials showing different ferroic order parameters and topologically protected states. This will lead to new science, developing the field of functional oxide materials in particular.
In addition to the significant scientific impact in the short to medium term, the research program will develop trained research personnel to fill positions available in Universities in the high technology areas such as thin film growth, micro- and nano-fabrication, transmission electron microscopy, etc., all in high demand in the UK. There will also be benefits in terms of this project's impact on the ability of the investigators of obtain funding for further research from European and US funding agencies, as well as to build collaborative links with new partners.
We will organise an international workshop focused on topologically protected state in ferroelectric materials that will ensure engagement with the scientific community and facilitate the establishment of new collaborations in the area. Outreach activities aimed particularly at local school pupils will be organize in collaboration with the Warwick Ogden Trust Teaching Fellow.
Our Regional Development Agency, Advantage West Midlands (and the European Regional Development Fund) funded in the past the Science City Initiative between Universities of Warwick and Birmingham for research into Advanced Materials. The aim of this initiative was to establish the region as an international competitor in materials Physics, undertaking world-class research in the development and characterisation of new materials for applications in a diverse range of industries. The present proposal will enhance the present capabilities in the area of Advanced Materials and stimulate research that will be beneficial to local, UK and European companies.

Publications

10 25 50
 
Description Significant outcome is revealed in the field of exotic phenomena in size-confined multiferroic systems, including topological domain states such as vortices, centre domains, and skyrmion and bubble domains. It has then been shown that polarisation induces interfacial breaking symmetry and polar phase in several neighbouring materials. The results are astonishing. For instance, polar ferromagnetic manganite and ruthenate layers are induced over significant thickness from their interface with ferroelectrics. This change the general picture of interfacial magnetoelectric effects based interface Dzyaloshinskii-Moriya interaction (iDMI). We have shown that not only skyrmions are induced in the ferromagnetic layers, but also more exotic ice spin phases found only in a handful of systems so far. Important influence this metal-ferroelectric interface, especially of the effective electronic properties including density of states, was shown in antiferroelectric and biferroic tunnel junctions.
A novel phase has been discovered in metal-ferroelectric-metal heterostructures with the thickness of ferroelectric layer in a narrow region of 8-12 unit cell. The ferroelectric arranges in a so-called incommensurate spin crystal phase mimicking the similar phase found in ferromagnetic materials under iDMI. This ferroelectric phase is the result of a newly discovered interaction namely electric DMI which is the analogous if magnetic DMI. The result is a highly ordered polar phase in which an initial periodic vortex state is modulated by a second periodicity normal on the direction of the first vortex periodicity. The result is cycloidally-modulated vortex phase.
Strain was discovered as playing a significant role in both electronic properties and domain structure. An emergent antipolar phase has been discovered that it is forming in bismuth ferrite - maganite superlattices. The emergent phase is characterized by an arrangement of a two unit cell thick lamella-like structure featuring antiparallel polarization, resulting an antiferroelectric-like structure typically associated with a morphotropic phase transition.
We have also shown that in PbTiO3 (PTO)-based multiferroic tunnel junctions (MFTJs) the ferroelectric domain pattern for PTO at a thickness of 9 unit cells (u.c.) is generally classic antiparallel (180°) with Ising type domain walls decorated with coupled clockwise and anti-clockwise vortices. For 6 u.c., a peculiar domain pattern with curling flux-closure type structures and incommensurate phase was observed. For only 3-u.c.-thick PTO films, domain structure is widely suppressed with polarization pointing out of plane and remanent domain structure.
Exploitation Route The polar vortices can in principle be at the basis of novel non-volatilel memory devices in which the information is encoded in the toroidal moment or chirality of the vortices instead of polarisation, is in the classical ferroelectric memories (FeRAMs), or magnetisation in MRAMs.
Sectors Digital/Communication/Information Technologies (including Software)

Education

Electronics

 
Description This grant has facilitated the emergence of several noteworthy scientific discoveries with significance in the field topological structures in ferroelectrics and connected ordered materials. Notable achievements are: An international research team, under the leadership of the Principal Investigator (PI) of the current grant, has made substantial strides in the identification and classification of topological entities integral to the overall properties of ferroic materials. Notably, topological domains such as vortex and skyrmion have been investigated for their potential role in enhancing the properties of ferroic materials. The primary focus of this endeavour is the development of high-density memory or logic devices, with the anticipation that these topological domains could provide benefits such as increased density, rapid switching, and energy-efficient read/write functionalities. Furthermore, the research initiative aims to deepen our understanding of metal-ferroelectric interfaces. The competition between the structures of these two materials is observed to be strongly influenced by the polarization direction and interface termination. This comprehensive exploration is anticipated to contribute valuable insights into the intricate dynamics governing metal-ferroelectric interfaces, paving the way for advancements in materials science and device applications. The grant has catalysed a flourishing research activity focused on polar interfaces, yielding highly creative outcomes, notably encapsulated in a pair of influential publications in Nature. One of these publications delves into polar interfaces, demonstrating notable interface piezoelectric and pyroelectric effects characterized by substantial coefficients and, significantly, freedom from symmetry limitations. These effects have been observed across a diverse spectrum of materials, encompassing conventional semiconductors, oxides, halide perovskites, and two-dimensional materials. The versatility of these effects renders them applicable in practical contexts within the realms of electromechanical and thermal phenomena. This includes applications in energy conversion and infrared sensors, exhibiting distinctive mechanisms and offering additional tuning feasibility. Importantly, these capabilities stand apart from those inherent in intrinsic non-centrosymmetric materials, thereby broadening the horizons of potential applications in the field. The second publication is centred around the revelation of a ground-breaking topological structure termed Ferroelectric Spin Ice. This discovery, coupled with the prior identification of polar vortices and skyrmions, contributes to the diminishing distinction between emergent ferromagnetic and ferroelectric dipole topologies. This development holds paramount significance as it offers a potential avenue for technological applications and establishes a rich framework for continued fundamental investigations into physical phenomena. These studies open up possibilities for exploring intricate ferroelectric topologies instigated by locally induced symmetry breaking through electric means. This parallels the investigation of topological spin textures observed in ferromagnetic materials, presenting a promising trajectory for expanding our understanding of the interplay between topology and ferroelectricity. Such advancements not only have implications for technological exploitation but also provide fertile ground for in-depth explorations into the fundamental aspects of these novel physical phenomena.
First Year Of Impact 2021
Sector Electronics
Impact Types Cultural

 
Description SiliNano
Geographic Reach Europe 
Policy Influence Type Participation in a guidance/advisory committee
URL https://www.sili-nano.de/advisory-board.html
 
Title Dataset for A Fast Frozen Phonon Algorithm Using Mixed Static Potentials 
Description Multislice simulation dataset for "A Fast Frozen Phonon Algorithm Using Mixed Static Potentials" 
Type Of Material Database/Collection of data 
Year Produced 2021 
Provided To Others? Yes  
URL https://zenodo.org/record/4883688
 
Title Dataset for Interlacing in atomic resolution scanning transmission electron microscopy 
Description Dataset for the publication: Interlacing in atomic resolution scanning transmission electron microscopy 
Type Of Material Database/Collection of data 
Year Produced 2023 
Provided To Others? Yes  
URL https://zenodo.org/record/7137494
 
Description Contributed talk XXI International Workshop on Physics of Semiconductor Devices (IWPSD 2021) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Contributed talk by Bhera Ram Tak, MM Yang, Vinay Gupta, YH Chu, Rajendra Singh, and Marin Alexe, "Flexible deep UV photodetectors on ß-Ga2O3 epitaxy", XXI International Workshop on Physics of Semiconductor Devices (IWPSD 2021) held at Indian Institute of Technology Delhi during December 14-17, 2021
Year(s) Of Engagement Activity 2021
 
Description Interfacial coupling in BFO/LSMO superlattices 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Contributed talk at IEEE ISAF-EMF-ICE-IWPM-PFM, EPFL, Switzerland, July 2019 presented by Wen Dong
Year(s) Of Engagement Activity 2019
URL https://ieee-uffc.org/news/2019-ieee-isaf-lausanne-july-2019/
 
Description Invited Talk 6th Workshop on Materials Physics 2021 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Invited talk to 6th Workshop on Materials Physics. Latest results on domain walls, vortices, and topological structures were reports and received a massive interest.
Year(s) Of Engagement Activity 2021
URL https://infim.ro/event/6th-edition-of-the-international-workshop-of-materials-physics-first-announce...
 
Description Invited Talk at at Young scientist PACE conference, Luxembourg 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Postgraduate students
Results and Impact Invited talk at a conference organised by and for young postgraduate students.
Year(s) Of Engagement Activity 2022
 
Description Invited Tlak Halle 2021 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Invited talk the Martin Luther University Halle, Germany
Year(s) Of Engagement Activity 2021
 
Description Loughborough University 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Postgraduate students
Results and Impact scientific talk presenting latest achievement at Warwick.
Year(s) Of Engagement Activity 2021,2022
 
Description Organisation of conference 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Organisation of the conference of the European Meeting on Ferroelectricity (EMF) part of the IEEE International Symposium on the Applications of Ferroelectrics (ISAF) was held at the Swiss Tech Convention Center near the EPFL in Lausanne, Switzerland, from July 14th to 19th, 2019 within the joint Conference, "F2cp2 2019", that united ISAF with several other international and European symposia :
-International Conference on Electroceramics (ICE);
-European Meeting on Ferroelectricity (EMF);
-International Workshop on PiezoMEMS (IWPM);
-Piezoresponse Force Microscopy Workshop (PFM).
Year(s) Of Engagement Activity 2019
URL https://ieee-uffc.org/news/2019-ieee-isaf-lausanne-july-2019/
 
Description Plenary lecture ISAF2021 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact This was a plenary lecture to the most important conference of the field of ferroelectrics.
Year(s) Of Engagement Activity 2021
URL https://isaf-isif-pfm2021.org
 
Description Polar exploration: Quantitative polarisation measurements in ferroelectric films 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Seminar to Trinity College Dublin presented by Jonathan JP Peters.
Year(s) Of Engagement Activity 2020
 
Description Polar exploration: Quantitative polarisation measurements in ferroelectric films 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Postgraduate students
Results and Impact Contributed talk to Oxford Microscopy (ATOM) XV workshop (24th Sep) presented by Jonathan JP Peters.
Year(s) Of Engagement Activity 2020
 
Description Property Optimization of Novel Dielectric Functional Materials and Devices 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Seminar at Yunnan University, Kunming, Yunnan, China, November 2020 presented by Wen Dong
Year(s) Of Engagement Activity 2020
 
Description Stabilising novel ferroic phases though interface engineering: The role of the TEM 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Contributed presentation to at Microscopy Society of Ireland Symposium 2021 (7th January)
Year(s) Of Engagement Activity 2018,2021
 
Description TU Dresden seminar 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Postgraduate students
Results and Impact Talk given by Samuel Seddon within the regular departmental seminar at TU Dresden. Attended by >50 people including undergraduate and postgraduate students. The latest results regarding the low-temperature AFMN investigations have been reported.
Year(s) Of Engagement Activity 2022
 
Description Talk APS March meeting 2021 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Talk presented by Sam Seddon et al., Real-space Observation of Ferroelectrically Induced Magnetic Spin Crystal in SrRuO3, at the APS march meeting 2021
Year(s) Of Engagement Activity 2021
URL https://meetings.aps.org/Meeting/MAR21/Session/J40.8
 
Description Talk attcube Munich 2022 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Professional Practitioners
Results and Impact Talk given by Samuel Seddon to attcube GmbH. Attended by >20 people mostly professional. The latest results regarding the low-temperature AFMN investigations have been reported.
Year(s) Of Engagement Activity 2022