New Publication: Time-domain imaging of curling modes in a confined magnetic vortex and a micromagnetic study exploring the role of spiral spin waves emitted by the core

Congratulations to David Osuna, whose paper, ‘Time-domain imaging of curling modes in a confined magnetic vortex and a micromagnetic study exploring the role of spiral spin waves emitted by the core’, was published this month in Physical Review B. David has recently finished his PhD in the CDT and is now a postdoctoral research fellow at University of Exeter, as part of the Electromagnetic and Acoustic Materials Group (EMAG).

David explains the paper’s topic:

“This was a very fruitful collaboration with Dr. Paul Keatley, finally published after about 3 years of hard work!

Generally speaking, we have modeled and ‘filmed’ oscillations of the atomic magnetic spins in microscopic magnets and related them to other dynamics revealed from simulations. Understanding this type of dynamics as a whole is key to design spintronic devices, that may be essential for processing information in quantum computers, for example.


The curling spin wave modes of a ferromagnetic vortex confined to a microscale disk have been directly imaged in response to a microwave field excitation using time-resolved scanning Kerr microscopy. Micromagnetic simulations have been used to explore the interaction of gyrotropic vortex core dynamics with the curling modes observed in the region of circulating in-plane magnetization. Hybridization of the fundamental gyrotropic mode with the degenerate, lowest frequency, azimuthal modes has previously been reported to lead to their splitting and counterpropagating motion, as we observe in our spectra and measured images. The curling nature of the modes can be ascribed to asymmetry in the static and dynamic magnetization across the disk thickness, but here we also present evidence that spiral spin waves emitted by the core can influence the spatial character of higher frequency curling modes for which hybridization is permitted only with gyrotropic modes of the same sense of azimuthal motion. While it is challenging to identify if such modes are truly hybridized from the mode dispersion in a confined disk, our simulations reveal that spiral spin waves from the core may act as mediators of the interaction between the core dynamics and azimuthal modes, enhancing the spiral nature of the curling mode. At higher frequency, modes with radial character only do not exhibit marked curling, but instead show evidence of interaction with spin waves generated at the edge of the disk. The measured spatiotemporal character of the observed curling modes is accurately reproduced by our simulations, which reveal the emission of propagating short-wavelength spiral spin waves from both core and edge regions of the disk. Our simulations suggest that the propagating modes are not inconsequential, but may play a role in the dynamic overlap required for hybridization of modes of the core and in-plane magnetized regions. These results are of importance to the fields of magnonics and spintronics that aim to utilize spin wave emission from highly localized, nanoscale regions of nonuniform magnetization, and their subsequent interaction with modes that may be supported nearby.

Fig. Time sequence of a radial-azimuthal spin wave mode simulated and experimentally imaged in a 2 micrometres diameter, 40 nm thick Permalloy disc with an in-plane RF excitation field at 10.24 GHz. Timestep is approximately 24 ps.

New Publication: An in situ investigation of the thermal decomposition of metal-organic framework NH2-MIL-125 (Ti)

Zahid Hussain

Congratulations to Zahid Hussain for his new paper, ‘An in situ investigation of the thermal decomposition of metal-organic framework NH2-MIL-125 (Ti)’ , recently published in Microporous and Mesoporous Materials.

Zahid explains the paper’s findings:

Metal-organic frameworks (MOFs) are exceptionally porous and highly crystalline coordination polymers. Since the late 1990s, MOFs have been intensively investigated for a large variety of applications such as gas separation and storage, energy storage and conversion, batteries, fuel cells, optoelectronics, sensing, supercapacitors, drug delivery and catalysis. However, many key questions need to be answered to optimize the synthesis of these materials for industrial-scale applications. In this study, we present an in-situ investigation of thermal conversion of a titanium-based MOF, NH2-MIL-125(Ti) under an inert atmosphere. In situ thermal analysis of NH2-MIL-125(Ti) reveals the presence of 3 defined stages of thermal transformation in the following order: phase-pure, highly porous, and crystalline MOF → intermediate amorphous phase without accessible porosity → recrystallized porous phase. The three stages occur from room temperature till 300 °C, between 350 and 550 °C and above ∼550 °C respectively. The derived disc-like particles exhibit a 35% volume shrinkage compared to the pristine MOF precursor. Highly crystalline N and/or C self-doped TiO2 nanoparticles are homogeneously distributed in the porous carbon matrix. The original 3D tetragonal disc-like morphology of the NH2-MIL-125(Ti) remains preserved in derived N and/or C doped TiO2/C composites. This study will provide an in-depth understanding of the thermal conversion behaviour of MOFs to rationally select and design the derived composites for the relevant applications.

The crystalline structure of Ti-MOF, NH2-MIL-125(Ti) and mechanism of its thermal decomposition.



We would also like to congratulate Zahid on passing his viva, and wish him the best of luck for his future career.

New Publication: Electrical Detection of DC Spin Current Propagation Through an Epitaxial Antiferromagnetic NiO Layer

David Newman

Congratulations to third year PGR David Newman, whose paper ‘Electrical Detection of DC Spin Current Propagation Through an Epitaxial Antiferromagnetic NiO Layer’ has recently been published in IEEE Transactions on Magnetics.

David explains this work and the impact of its findings:

Spin currents (net transfer of spin angular momentum) have been suggested as potential successors to charge currents in areas like magnetic data storage. A spin current can be generated by a mechanism known as ‘spin pumping’ whereby a ferromagnetic (FM) layer is excited into resonance and then ‘pumps’ a spin current into an adjacent nonmagnetic (NM) layer. Recently, work has even found that antiferromagnetic (AFM) layers could even be used to amplify the amount of spin current produced.


The main issue comes with the difficulty in observing a pure spin current. Current techniques mainly consist of detecting the spin transfer torque exerted on an additional FM layer (AC spin current). Alternatively, the DC spin current can be observed by the transverse charge current generated by a spin current propagating through a heavy metal (like Pt) via the inverse spin Hall effect (ISHE).


In our work, we measure the ISHE on a sample with an AFM layer where the AC spin current has already been detected (see separate publication: and, with some experimental considerations, extract the DC spin current. By showing AC and DC spin current components can be observed in the same sample, this work provides the pathway to a more complete perspective of spin current propagation through an AFM layer which is important in the development of spintronic technologies in areas such as magnetic data storage.

New Publication: Graphene coated fabrics by ultrasonic spray coating for wearable electronics and smart textiles

Kavya Sadanandan

Congratulations to third year PGR Kavya Sadanandan, whose paper ‘Graphene coated fabrics by ultrasonic spray coating for wearable electronics and smart textiles’ was recently published in Journal of Physics: Materials.


The seamless incorporation of electronics in textiles have the potential to enable various applications ranging from sensors for the internet of things to personalised medicine and human-machine interfacing. Graphene electronic textiles are a current focus for the research community due to the exceptional electrical and optical properties combined with the high flexibility of this material, which makes it the most effective strategy to achieve ultimate mechanical robustness of electronic devices for textile integrated electronics. An efficient way to create electronic textiles is to fabricate devices directly on the fabric. This can be done by coating the textile fabric with graphene to make it conductive. Here we discuss successful and efficient methods for coating graphene nanoplatelets on textile substrates of nylon, polyester and meta-aramid using ultrasonic spray coating technique. These coatings are characterised by scanning electron microscopy, contact angle and electrical conductivity measurements in order to identify the optimal textile electrode.  Our study provides the foundation for the large-area fabrication of graphene electronic textiles.

New Publication: Bimetal-organic framework derived multi-heterostructured TiO2/CuxO/C nanocomposites with superior photocatalytic H2 generation performance

Congratulations to final year PGR Zahid Hussain for his new publication ‘Bimetal-organic framework derived multi-heterostructured TiO2/CuxO/C nanocomposites with superior photocatalytic H2 generation performance’, which was recently published in Journal of Materials Chemistry A (JMCA).

In this work, In-situ formation of p-n heterojunctions between TiO2 and CuxO in heteroatoms-doped carbon nanocomposites and their applications in photocatalytic H2 evolution were demonstrated. One-step pyrolysis of bimetal-organic-frameworks NH2-MIL-125(Ti/Cu) in water steam at 700 ºC forms phasejunction between nitrogen/carbon co-doped anatase and rutile TiO2, accompanied by the formation of CuxO heterostructures. Moreover, p-n heterojunction is also formed between TiO2/CuxO nanoparticles. These multi-heterostructures are embedded in N-containing and hydrophilic carboxyl functionalised carbon. The optimised TiO2/CuxO/C composites absorb more visible light and offer multiple pathways for photoinduced electrons and holes migration. Also, these nanocomposites provide increased active sites for photocatalytic reactions. Without loading expensive noble metals, TiO2/CuxO/C nanocomposites exhibited superior photocatalytic H2 generation activity of 3298 µmol gcat-1 h-1 under UV-Visible light, 40 times higher than commercial TiO2. This work offers a simple approach to fabricate novel photocatalytic nanocomposites for efficient H2 generation.

Zahid’s previous publications include a translation of Carlo Rovelli’s “Seven Brief Lessons on Physics” into Urdu and ‘Surface functionalized N-C-TiO2/C nanocomposites derived from metal-organic framework in water vapour for enhanced photocatalytic H2 generation’ , of which he was lead author, published in Journal of Energy Chemistry.

New Publication: Tunable pseudo-magnetic fields for polaritons in strained metasurfaces

Congratulations to final year PhD student Charlie-Ray Mann whose theory paper, entitled ‘Tunable pseudo-magnetic fields for polaritons in strained metasurfaces’, has been published in the prestigious journal Nature Photonics.

The work has also been featured on the University of Exeter’s news website.

Charlie-Ray Mann, the lead scientist and author of the study, explains:

Charlie-Ray Mann- lead scientist and author of the paper published in Nature Photonics

The interaction between charged particles and magnetic fields gives rise to some of the most fascinating phenomena in physics, ranging from the beautiful Aurora Borealis to the famous quantum-Hall effect. Unfortunately, because photons do not have an electric charge they are inert to real magnetic fields as they do not experience a Lorentz force.

Taking inspiration from graphene physics, we have shown that you can generate `artificial’ magnetic fields for light by distorting honeycomb metasurfaces in a specific way. These distortions generate a ‘synthetic’ Lorentz force which can deflect the surface polaritons into effective cyclotron orbits, and for larger distortions one can also observe Landau quantization of the polaritons — phenomena once thought to be exclusive to charged particles.

However, the main drawback with this approach is that to change the artificial magnetic field one is usually required to modify the distortion in the lattice. This is extremely challenging, if not impossible to do with photonic structures, hindering our ability to tune the artificial magnetic field after the structure has been fabricated — that is, the artificial magnetic fields are usually fixed by design.

In this theoretical work we have proposed an alternative mechanism to tune the artificial magnetic fields, which requires no change to the metasurface distortion. By exploiting the hybrid light-matter character of the surface polaritons, we show that one can tune the artificial magnetic field by modifying the real electromagnetic environment surrounding the metasurface.

Specifically, we’ve shown that by embedding the metasurface inside a photonic cavity or waveguide, one can tune the artificial magnetic field by modifying a single external parameter: the cavity width. In fact, we’ve even demonstrated that you can switch off the artificial magnetic entirely at a critical cavity width, without having to remove the distortion in the metasurface — something that is impossible to do in graphene or any system that emulates graphene.

Using this new mechanism you can bend the trajectory of the polaritons using a tunable Lorentz-like force that can be switched on/off, and you can drastically reconfigure the polariton Landau level spectrum by simply changing the cavity width.

Earlier this year, Charlie-Ray Mann was awarded a £5,000 prize from the Rank Prize Funds 2020.

New Publication: Calcium-stannous oxide solid solutions for solar devices

Ned Taylor

Congratulations to final year PGR Ned Taylor, who is lead author of ‘Calcium-stannous oxide solid solutions for solar devices’, published in Applied Physics Letters last week.

Ned gives a short summary of his work:

In this work, the potential of calcium-doped stannous oxide is explored for its potential as an active layer in an all-oxide solar cell design. The authors find an alloy formed of doping Sn:Ca with ratio 7:1 in SnO to exhibit favourable electronic and optical properties for a photovoltaic material. A potential design is proposed for an all-oxide solar cell based around the aforementioned solid solution being the active layer, where TiO2 and CaO are the adjacent transport layers. This study is performed using first principles density functional theory methods to explore the systems. This work was funded jointly be the CDT and Solaris Photonics, with the work being conducted by Ned Taylor and Steve Hepplestone.

Ned’s previous publications include ‘The Fundamental Mechanism Behind Colossal Permitivity in Oxides’, which he co-authored with fellow CDT PGRs Francis Davies, Shane Davies and Conor Price.

New Publication: Zahid Hussain translates “Seven Brief Lessons on Physics” into Urdu

Final year PGR Zahid Hussain in partnership with Fasi Malik, University of California has translated Carlo Rovelli’s “Seven Brief Lessons on Physics” into Urdu. Their translation has just been published by Mashal Books, Lahore. Below, Zahid discusses his motivations and the importance of the book:

I am pleased to announce that our translation of Carlo Rovelli’s book “Seven Brief Lessons on Physics” into Urdu (Pakistan’s national language) has been published by Mashal Books, Lahore. This work is a part of my outreach activities under CDT Metamaterials XM2 to promote science to inspire young students and also, the general public. The reason for translating this interesting book into Urdu is to introducing new scientific developments and concepts of physics in a simple and easy-to-understand language. Secondly, I find it very useful to promote such work to those curious readers who cannot access them in English. A short description of the book is given below:

The book provides a very brief overview of the most fascinating aspects of the great intellectual revolution that has occurred in physics in the twentieth century. In a very simple language, Carlo Rovelli explains to us that the image of the world our ancestors carried with them in prehistoric times, was challenged by the Greek philosophers. Later on, Galileo, Copernicus and Newton’s scientific contributions caused a paradigm shift in our perception of the reality. Afterwards, in the wake of the 20th century, the birth of Quantum mechanics and Albert Einstein’s theory of relativity provided us with a new understanding of the physical world we live in. Now, we know that either it’s a world of very small objects (at the atomic scale) or the world of bigger objects which we can see with our eyes, the reality is quantized. Everything, known in this material universe and even all the fundamental forces of nature interact with matter through the particles. The most fascinating aspect of this simple book is that it leaves the reader with this conclusion that science shows us how to better understand the world and also reveals to us that just how vast is the extent of what is still not known.

Zahid began his translation in 2018, with three chapters published online, so this is the culmination of years of dedication. Congratulations to Zahid for this great achievement.

New Publication: ‘Surface functionalized N-C-TiO2/C nanocomposites derived from metal-organic framework in water vapour for enhanced photocatalytic H2 generation’

Congratulations to PGR Zahid Hussain, who is lead author of the paper  ‘Surface functionalized N-C-TiO2/C nanocomposites derived from metal-organic framework in water vapour for enhanced photocatalytic H2 generation’, published in the Journal of Energy Chemistry.

Zahid’s previous publications include ‘MOF Derived Porous ZnO/C Nanocomposites for Efficient Dye Photodegradation’
published in ACS Applied Energy Materials, and ‘Structural, optical, electronic and magnetic properties of multiphase ZnO/Zn(OH)2/ZnO2 nanocomposites and hexagonal prism shaped ZnO nanoparticles synthesized by pulse laser ablation in Heptanes’  published in Elsevier Materials Chemistry and Physics.


In this work, we have successfully demonstrated that nitrogen/carbon co-doped (anatase and rutile) TiO2 phase junction nanoparticles, homogeneously distributed in N and carboxyl group functionalized porous carbon matrix can be synthesized via simple one-step pyrolysis of titanium-based metal-organic framework (Ti-MOFs), NH2-MIL-125(Ti). Introducing water vapour at high temperature during the pyrolysis of NH2-MIL-125(Ti) results in the functionalization of the carbon matrix with carboxyl groups as well as the creation of additional localized oxygen-rich N like interstitial/intraband states above the valence band of polymorphic TiO2 nanoparticles that further narrowed the energy bandgap. The derived N-C-TiO2/C phase junction composites retain the disc-like tetragonal morphologies and textural properties inherited from the NH2-MIL-125(Ti) precursor. Without loading any noble metal co-catalyst such as Pt, Au, Pd, the sample N–C-TiO2/CArW exhibits very promising photocatalytic H2 generation from water splitting.

New Publication: Coupling and confinement of current in thermoacoustic phased arrays

Credit: David Tatnell

Congratulations to third year PGR David Tatnell, whose publication ‘Coupling and confinement of current in thermoacoustic phased arrays’ has just been published in Science Advances and featured on the University’s research news webpage.

David, lead author of this study into thermoacoustic arrays, says:

This work is the first experimental demonstration of thermoacoustic sources in acoustic phased arrays.

We find that thermoacoustic arrays are capable of reproducing all of the effects of traditional speaker arrays, such as beam forming and steering, but also have additional characteristics unique to this generation mechanism.

We show that we can exploit these characteristics to radically simplify array design, allowing for thermoacoustic phased arrays to be made smaller, and more economically, than traditional speakers. This includes creating a fully controlled array from nothing more than a thin metal film attached to some metal wires. Combined with the ability to make the speakers flexible and transparent, thermoacoustic arrays have many potential applications, such as haptic feedback systems in smartphones and other wearables.

This paper represents two and a half years of hard work, sponsored by QinetiQ and EPSRC.

Check out the University’s main research news webpage, which explores these findings and their significance in further detail.