arXiv subjects

T. Thomson

Publications and source records attributed to T. Thomson.

6 recordsLinked to original sources

arXiv2025

Ultrafast Laser-Induced Magnetic Relaxation in Artificial Spin Ice Driven by Dipolar Interactions

It is of great interest to develop methods to rapidly and effectively control the magnetic configurations in artificial spin ices, which are arrangements of dipolar coupled nanomagnets that have a variety of fascinating collective magnetic phenomena associated with them. This is not only valuable in terms of acquiring fundamental understanding but is also important for future high-performance applications. Here, we demonstrate ultrafast control of magnetic relaxation in square artificial spin ice through femtosecond laser pulsed excitation, enabling rapid access to low-energy states via dipolar interactions. Time-resolved magneto-optical Kerr effect measurements reveal that, after laser-induced demagnetization, the magnetization recovers within picoseconds. During this brief transient window, dipolar coupling drives a collective magnetic ordering. Ex-situ magnetic force microscopy confirms the emergence of extended Type I vertex domains, characteristic of ground-state ordering, thus establishing ultrafast laser-driven relaxation as a route to attain the low-energy states. Through complementary energy barrier calculations and micromagnetic simulations incorporating Landau-Lifshitz-Bloch dynamics, we elucidate the underlying mechanism: transient ultrafast demagnetization followed by rapid remagnetization that enables a dipolar-driven collective rearrangement. Moreover, a tailored decreasing-fluence laser annealing protocol is shown to enhance ground-state ordering, consistently achieving over 92% ground-state vertex populations. This work opens the way to ultrafast and spatially selective control of magnetic states in artificial spin ice for spin-based computation and memory technologies, and highlights the critical interplay of thermal fluctuations, magnetostatic coupling, and transient magnetization dynamics.

cond-mat.mes-hall↗

arXiv2024

Materials for Quantum Technologies: a Roadmap for Spin and Topology

In this Perspective article, we explore some of the promising spin and topology material platforms (e.g. spins in semi- and superconductors, skyrmionic, topological and 2D materials) being developed for such quantum components as qubits, superconducting memories, sensing, and metrological standards and discuss their figures of merit. Spin- and topology-related quantum phenomena have several advantages, including high coherence time, topological protection and stability, low error rate, relative ease of engineering and control, simple initiation and read-out. However, the relevant technologies are at different stages of research and development, and here we discuss their state-of-the-art, potential applications, challenges and solutions.

cond-mat.mes-hall↗

arXiv2024

Tunable Ultra-Strong Magnon-Magnon Coupling Approaching the Deep-Strong Regime in a van der Waals Antiferromagnet

Antiferromagnetic (AFM) magnons in van der Waals (vdW) materials offer substantial potential for applications in magnonics and spintronics. In this study, we demonstrate ultra-strong magnon-magnon coupling in the GHz regime within a vdW AFM, achieving a maximum coupling rate of 0.91. Our investigation shows the tunability of coupling strength through temperature-dependent magnetic anisotropies. We compare coupling strength values derived from the gap size from the measured spectrum with those calculated directly through the coupling parameter and show that the gap size as a measure of coupling strength is limited for the ultra-strong coupling regime. Additionally, analytical calculations show the possibility to reach the deep-strong coupling regime by engineering the magnetic anisotropy. These findings highlight the potential of vdW AFMs as a model case to study magnetisation dynamics in low-symmetry magnetic materials.

cond-mat.mes-hall↗

arXiv2020

Anisotropy induced spin re-orientation in chemically-modulated amorphous ferrimagnetic films

The ability to tune the competition between the in-plane and out-of-plane orientation of magnetization provides a means to construct thermal sensors with a sharp spin re-orientation transition at specific temperatures. We have observed such a tuneable, temperature driven spin re-orientation in structurally amorphous, ferrimagnetic rare earth-transition metal (RE-TM) alloy thin films using scanning transmission X-ray microscopy (STXM) and magnetic measurements. The nature of the spin re-orientation transition in FeGd can be fully explained by a non-equilibrium, nanoscale modulation of the chemical composition of the films. This modulation leads to a magnetic domain pattern of nanoscale speckles superimposed on a background of in-plane domains that form Laudau configurations in micron-scale patterned elements. It is this speckle magnetic structure that gives rise to a sharp two step-reversal mechanism that is temperature dependent. The possibility to balance competing anisotropies through the temperature opens opportunities to create and manipulate topological spin textures.

cond-mat.mtrl-sci↗

arXiv2012

Spin-half paramagnetism in graphene induced by point defects

Using magnetization measurements, we show that point defects in graphene - fluorine adatoms and irradiation defects (vacancies) - carry magnetic moments with spin 1/2. Both types of defects lead to notable paramagnetism but no magnetic ordering could be detected down to liquid helium temperatures. The induced paramagnetism dominates graphene's low-temperature magnetic properties despite the fact that maximum response we could achieve was limited to one moment per approximately 1000 carbon atoms. This limitation is explained by clustering of adatoms and, for the case of vacancies, by losing graphene's structural stability.

cond-mat.mes-hall↗

arXiv2011

Tunable Magnonic Frequency and Damping in [Co/Pd]8 Multilayers with Variable Co Layer Thickness

We report the experimental observation of collective picosecond magnetization dynamics in [Co/Pd]8 multilayers with perpendicular magnetic anisotropy. The precession frequency shows large and systematic variation from about 5 GHz to about 90 GHz with the decrease in the Co layer thickness from 1.0 nm to 0.22 nm due to the linear increase in the perpendicular magnetic anisotropy. The damping coefficient 'alpha' is found to be inversely proportional to the Co layer thickness and a linear relation between the perpendicular magnetic anisotropy and 'alpha' is established. We discuss the possible reasons behind the enhanced damping as the d-d hybridization at the interface and spin pumping. These observations are significant for the applications of these materials in spintronics and magnonic crystals.

cond-mat.mes-hall↗