Massively parallel symplectic algorithm for coupled magnetic spin dynamics and molecular dynamics

Tranchida, Julien; Plimpton, Steven J.; Thibaudeau, Pascal; Thompson, Aidan P.

doi:10.1016/j.jcp.2018.06.042

Cited by 114 publications

(125 citation statements)

References 99 publications

(114 reference statements)

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“…4b of the main text. The simulations have been carried out using the SPIN package of LAMMPS [36,37] which assesses spin textures and their dynamics by solving the Landau-Lifshitz-Gilbert (LLG) equation :…”

Section: Atomistic Spin Dynamic Computationmentioning

confidence: 99%

“…Interestingly, the measured hot spots on the scanning NV magnetometry image can be considered as the embryos of multi-q topological objects, especially as the dichroic diffraction patterns evidence their chirality. In order to better illustrate this DW effect, we have carried out numerical simulations using a dynamical atomistic magnetic simulations code 28 . We minimized the convergence time by dividing all distances by 10 and correspondingly multiplying by 10 the magnetoelectric interactions.…”

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confidence: 99%

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Electric and antiferromagnetic chiral textures at multiferroic domain walls

et al. 2019

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Chirality, a foundational concept throughout science, may arise at ferromagnetic domain walls 1 and in related objects such as skyrmions 2. However, chiral textures should also exist in other types of ferroics such as antiferromagnets for which theory predicts that they should move faster for lower power 3 , and ferroelectrics where they should be extremely small and possess unusual topologies 4,5. Here we report the concomitant observation of antiferromagnetic and electric chiral textures at domain walls in the room-temperature ferroelectric antiferromagnet BiFeO 3. Combining reciprocal and real-space characterization techniques, we reveal the presence of periodic chiral antiferromagnetic objects along the domain walls as well as a priori energetically unfavorable chiral ferroelectric domain walls. We discuss the mechanisms underlying their formation and their relevance for electrically controlled topological oxide electronics and spintronics. Metallic ferromagnets have been the elemental bricks of spintronics for the last three decades and continue to hold promises on the basis of non-collinear chiral spin textures such as skyrmions. These topologically protected objects are envisioned to be the future of magnetic data storage thanks to their specific stability, dynamics, and scalability 2. In parallel, antiferromagnets (AFs) are emerging as a new paradigm for spintronics 6. They are intrinsically stable (being insensitive to spurious magnetic fields), scalable (no cross talk between neighbouring memory cells), and fast (switching frequencies in the THz regime). The opportunity of gathering the best of these two worlds and realize "antiferromagnetic skyrmions" is then tremendously appealing but faces at least two major challenges. The first one is to achieve antiferromagnetic chirality and the second one is to identify appropriate control stimuli to create, annihilate and move these chiral objects. On one hand, chirality may naturally emerge at domain walls. The antiferromagnetic domain wall structure is a virtually uncharted territory but this is where translational symmetry is broken and spin rotation favoured. On the other hand, AF manipulation is hampered by the intrinsic lack of net magnetization, which prevents a straightforward magnetic actuation. This fundamental issue may be

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Section: Atomistic Spin Dynamic Computationmentioning

confidence: 99%

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confidence: 99%

Electric and antiferromagnetic chiral textures at multiferroic domain walls

et al. 2019

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“…(1)), coupled to white-noise processes. For a single magnetic moment, getting that equation for ASD simulations has been considered from a quantum perspective [18,32,33], and several numerical implementations have been reported [17,34,35], including the exchange interaction, the treatment of external and anisotropic magnetic fields and temperature.…”

Section: A Reference Modelmentioning

confidence: 99%

“…More details of this integration method have been provided in previous works [35,39]. These ASD simulations are performed for different noise realizations and averages are taken.…”

Section: A Reference Modelmentioning

confidence: 99%

Hierarchies of Landau-Lifshitz-Bloch equations for nanomagnets: A functional integral framework

2018

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We propose a functional integral framework for the derivation of hierarchies of Landau-Lifshitz-Bloch (LLB) equations that describe the flow towards equilibrium of the first and second moments of the magnetization. The short scale description is defined by the stochatic Landau-Lifshitz-Gilbert equation, under both Markovian or non-Markovian noise, and takes into account interaction terms that are of practical relevance. Depending on the interactions, different hierarchies on the moments are obtained in the corresponding LLB equations. Two closure Ansätze are discussed and tested by numerical methods that are adapted to the symmetries of the problem. Our formalism provides a rigorous bridge between the atomistic spin dynamics simulations at short scales and micromagnetic descriptions at larger scales.

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“…Next, we extend the equilibrium calculations to a ferromagnetic quench. We go on to study the equilibrium and out of equilibrium properties using a combination of Monte Carlo simulations -already widely applied in the characterization of bulk systems [12,13] -and atomistic spin dynamics, [14,15], respectively. The dynamics are explored through the numerical implementation of the Landau-Lifshitz-Gilbert [16] equation extended to deal with finite temperatures within a Langevin dynamics framework.…”

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confidence: 99%

Nanoscopic time crystal obtained by nonergodic spin dynamics

Lupo

Weber

2019

Phys. Rev. B

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We study the far-from-equilibrium properties of quenched magnetic nanoscopic classical spin systems. In particular, we focus on the interplay between lattice vibrations and magnetic frustrations induced by surface effects typical of an antiferromagnet. We use a combination of Monte Carlo simulations and explore the dynamical behaviours by solving the stochastic Landau-Lifshitz-Gilbert equation at finite temperature. The Monte Carlo approach treats both the ionic degrees of freedom and spin variables on the same footing, via an extended Lennard-Jones Hamiltonian with a spinlattice coupling. The zero temperature phase diagram of the finite size nanoscopic systems with respect to the range of the Heisenberg interaction and the Lennard-Jones coupling constant shows two main structures with non-trivial magnetisation triggered by antiferromagnetism: a simple cubic and a body-centred cubic. At non zero temperature, the competition between spins and the ionic vibrations considerably affects the magnetization of the system. Exploring the dynamics reveals a non-trivial structural induced behaviour in the spin relaxation with a concomitant memory of the initially applied ferromagnetic quench. We report the observation of a non-trivial dynamical scenario, obtained after a ferromagnetic magnetic quench at low temperature. Furthermore, we observe long-lived non-thermal states which could open new avenues for nano-technology.Many-body systems comprise a wide range of systems, from simple metals, organic molecules, all the way up to cells. While their physics can be extremely rich, this complexity is however often irrelevant, as such systems will typically -at equilibrium -thermalise, a process through which most information about their preparation history and their initial state is lost [1,2]. This behaviour is typical for ergodic systems in the thermodynamic limit and allows to calculate physical observables and make predictions that can be measured and tested. However, ergodicity can be broken out-of-equilibrium [3], in particular by inducing non-thermal states that keep a memory of their initial condition for long times. Those peculiar behaviours have been explored in novel nonequilibrium phases of matter, which includes Floquet symmetry protected topological phases [4] and time crystals [5,6]. While bulk systems have been extensively investigated, nanoscopic systems remain open to questions. Recent progress in nano-engineering and the design of nanoscopic systems, such as nano-magnets made of single atoms arrays as memory devices [7], has opened new possibilities to explore quantum states in systems where thermalisation is not obtained, in particular for quenched and periodically-driven systems. Indeed, it has been observed that finite size effects allow these systems to keep a much better local memory of their initial conditions [8]. Experimental advances in manipulation and switching of the magnetization -possible even at the femtosecond level [9]-have triggered new studies in spin dynamics towards the microscopic underst...

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Massively parallel symplectic algorithm for coupled magnetic spin dynamics and molecular dynamics

Cited by 114 publications

References 99 publications

Electric and antiferromagnetic chiral textures at multiferroic domain walls

Electric and antiferromagnetic chiral textures at multiferroic domain walls

Hierarchies of Landau-Lifshitz-Bloch equations for nanomagnets: A functional integral framework

Nanoscopic time crystal obtained by nonergodic spin dynamics

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