Speaker: Young-Gwan Choi, Post-Doctoral Researcher, Max Planck Institute for Chemical Physics of Solids, Dresden, Germany.

The experimental observation of the orbital Hall effect (OHE) in a light metal Ti using the magneto-optical Kerr effect (MOKE) will be presented. The OHE is the generation of electron orbital angular momentum flow transverse to an external electric field, and although circumstantial evidence has been growing, direct detection has remained elusive. Previously, theoretical studies predicted that the OHE is a fundamental origin of the spin Hall effect (SHE) in many transition metals. Our experimental results confirm the existence of the OHE in a light element metal Ti with an unexpectedly long orbital relaxation length, ~70 nm. We found that the MOKE signal due to the OHE -induced orbital moment is orders of magnitude larger than that due to the spin moment induced by the SHE in Ti. Moreover, we examined the torque efficiency and the orbital relaxation length using orbital torque experiments with a ferromagnet layer. This observation challenges the belief that orbital angular momentum is quenched in solids. The presentation will also discuss the potential of using the orbital degree of freedom as an information carrier and the importance of studying the orbital degree of freedom. The findings significantly impact the electrical control of magnetism and underscore the need for an improved understanding of OHE dynamics in various materials. Moreover, this presentation will also explore further directions for OHE studies using other techniques such as nitrogen-vacancy scanning and x-ray circular dichroism.

http://talks.cam.ac.uk/talk/index/216436

Speaker: Dr Wenshuo Xu, Department of Materials Science & Metallurgy, University of Cambridge

25 minutes plus questions unless stated otherwise (please arrive a few minutes early to start on time)

Drop in and explore the world of materials science through our table-top displays and interactive activities. Find out how we can make electricity from colourful windows, investigate how our technology wastes energy, see a wire change shape by itself and use a microscope to look at what’s inside a piece of metal.

Our activities are suitable for all ages, and researchers will be on hand to answer your questions! Come along and see how our world-leading science will power tomorrow’s technologies and have an impact on the world we live in.

Suitable for ages 5yrs+.

Speaker: James Moloney, Department of Materials Science & Metallurgy, University of Cambridge

25 minutes plus questions unless stated otherwise (please arrive a few minutes early to start on time)

Speaker: Dr Chiara Gattinoni, Dept. of Physics, Kings College, London

The behaviour of nanoscale forms of matter, such as thin films or nanocrystal, is strongly influenced by the structure and behaviour of their surfaces and interfaces. In nanoscale ferroelectrics, a surface charge arises as a consequence of the ferroelectric polarization itself, and this surface charge leads to an electrostatic instability – the so-called “polar catastrophe” – if it is not compensated. Here we show how the properties of ferroelectric materials at the nanoscale are intimately linked to the compensation mechanism that takes place at their surface. We also demonstrate how the structural and electronic properties of PbTiO₃, BiFeO₃ and KTaO₃ lead to a different compensation mechanism in each case, and we discuss how to harness the properties of these nanoscale materials for applications in microelectronics and catalysis.

http://talks.cam.ac.uk/talk/index/211096

Speaker: Dr Mehmet Egilmez, American University of Sharjah, UAE

High/medium entropy alloys have attracted great scientific and industrial interest during the last two decades. In general, these alloys consist of 3 to 7 (or more) elements in large percentages, which leads to a high degree of disorder and hence a very large configurational entropy. In these alloys, the utilization of a large number of elements results in rich compositional tuning, which in turn results in exciting mechanical, electrochemical, magnetic, and electronic functionalities.  The talk will present our recent efforts on the CoNiCr(V) medium-entropy system and TiZrNbSn shape memory alloy superconductor. The CoNiCr system is particularly interesting because it possesses exceptional mechanical properties across a wide range of temperatures, excellent corrosive resistance, electrochemical functionalities, and unique transport and magnetic properties. The extraordinary properties of this system not only are due to differences in atomic radii and electronic configurations of constituent elements but are also dependent on the magnetically driven chemical short-range order.

25 minutes plus questions unless stated otherwise (please arrive a few minutes early to start on time)

Speaker: Dr Mengfan Guo, Department of Materials Science & Metallurgy, University of Cambridge

25 minutes plus questions unless stated otherwise (please arrive a few minutes early to start on time)

Speaker: Dr Lutz Kirste, Fraunhofer Institute for Applied Solid State Physics (IAF), Freiburg, Germany.

http://talks.cam.ac.uk/talk/index/211093

Speaker: Professor Bilge Yildiz, Massachusetts Institute of Technology, Cambridge, USA

Abstract:

Exsolution is an effective approach to fabricating oxide-supported metal nanoparticle (electro-)catalysts via phase precipitation out of a host oxide. A fundamental understanding and control of the exsolution kinetics are needed to engineer the size, density and composition of exsolved nanoparticles to obtain higher catalytic activity toward clean energy and fuel conversion reactions, such as in solid oxide fuel and electrolysis cells. Since oxygen release via oxygen vacancy formation in the host oxide is behind oxide reduction and metal exsolution, we hypothesize that the kinetics of metal exsolution should depend on the kinetics of oxygen release. In this work, we probe the surface exsolution kinetics both experimentally and theoretically using thin-film perovskite oxide model systems, show its relation to the oxygen evolution kinetics, and tune it by external drivers including elastic strain and ion irradiation. Using both drivers, we couple to the formation of point defects and defect clusters, that serve as nucleation sites for nanoparticle exsolution. As a result, we can controllably tune size, density, composition and position of the exsolved metal nanoparticles. This finding can guide the design of exsolution electrocatalysts to advance the performance and durability of solid oxide electrochemical cells.

http://talks.cam.ac.uk/talk/index/211003

Speaker: Dr Remko Fermin, Department of Materials Science & Metallurgy, University of Cambridge

Abstract:
Generally, superconductivity and magnetism are two antagonistic processes. However, advances of the last 20 years have shown that, utilizing non-collinear magnetic layers or spin-orbit coupling, unconventional supercurrents can be generated that can penetrate ferromagnets over long length scales (so called long-range spin-triplet supercurrents). Even though the alternative generation of spin-triplet supercurrents using magnetic structures, such as domain walls and vortices, has been the subject of intense theoretical discussions, the relevant experiments remain scarce. During this talk, I will present our results on nanostructured Josephson junctions with a highly controllable spin texture, based on disk- and ellipse-shaped Nb/Co bilayers. We use the vortex magnetization of the cobalt in disk-shaped junctions to induce long-range triplet (LRT) superconductivity in the ferromagnet. Surprisingly, the LRT correlations emerge in highly localized (sub-80 nm) channels at the rim of the ferromagnet, despite its trivial band structure. We show that these robust rim currents arise from the magnetization texture acting as an effective spin–orbit coupling, which results in spin accumulation at the bilayer–vacuum boundary. Our approach, that combines micromagnetic modeling with microstructured SF-hybrids, presents a novel route towards studying effective spin-orbit coupling of magnetic textures, LRT generation and, realizing superconducting memory applications.

25 minutes plus questions unless stated otherwise (please arrive a few minutes early to start on time)