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Antiferromagnets (AFMs) are strong candidates for the future spintronic and memory applications largely because of their inherently fast dynamics and lack of stray fields, with Mn2Au being one of the most promising. For the numerical modelling of magnetic material properties, it is common to use ab-initio methods, atomistic models and micromagnetics. However, each method alone describes the physics within certain limits. Multiscale methods bridging the gap between these three approaches have been already proposed for ferromagnetic materials. Here, we present a complete multiscale model of the AFM Mn2Au as an exemplar material, starting with results from ab-initio methods going via atomistic spin dynamics (ASD) to an AFM Landau-Lifshitz-Bloch (AFM-LLB) model. Firstly, bulk is modelled using a classical spin Hamiltonian constructed based on earlier first-principles calculations. Secondly, this spin model is used in the stochastic Landau-Lifshitz-Gilbert (LLG) to calculate temperature-dependent equilibrium properties, such as magnetization and magnetic susceptibilities. Thirdly, the temperature dependent micromagnetic parameters are used in the AFM-LLB. We validate our approach by comparing the ASD and AFM-LLB models for three paradigmatic cases; (i) Damped magnetic oscillations, (ii) magnetization dynamics following a heat pulse resembling pump-probe experiments, (iii) magnetic domain wall motion under thermal gradients., Comment: 14 pages, 12 figures

In this work, we present evidence for the existence of a magnonic current on the sub-picosecond time-scale in a ferrimagnetic bilayer and its effect on ultrafast spin dynamics. The ferrimagnet, GdFeCo, is a material known to undergo ultrafast switching within 1-2ps after excitation with femtosecond laser pulses. Here, we show that the strong thermal gradients induced by applying femtosecond laser pulses and the presence of chemical inhomogeneities lead to local imbalances in the effective temperatures of the spins that produces a rapid transfer of spin angular momentum, which we interpret as an ultrafast spin Seebeck effect. We have quantified the typical magnon propagation in such a system. The results show ballistic magnon propagation with 30nm/ps velocities. The characteristic time scale of such magnon propagation indicates that this magnon transport can play an important role in switching, a crucial piece of understanding towards realising next generation data processing devices that operate at much higher frequencies., Comment: 6 pages, 4 figures

The complex magnetic properties of Fe/Ir/Fe sandwiches are studied using a hierarchical multi-scale model. The approach uses first principles calculations and thermodynamic models to reveal the equilibrium spinwave, magnetization and dynamic demagnetisation properties. Finite temperature calculations show a complex spinwave dispersion and an initially counter-intuitive, increasing exchange stiffness with temperature (a key quantity for device applications) due to the effects of frustration at the interface, which then decreases due to magnon softening. Finally, the demagnetisation process in these structures is shown to be much slower at the interface as compared with the bulk, a key insight to interpret ultrafast laser-induced demagnetization processes in layered or interface materials., Gino Hrkac (GH) acknowledges support from the Vienna Science and Technology Fund (WWTF) under Grant No. MA14-44, through the EPSRC Grant No. EP/K008412/1, and from the Royal Society under Grant No. UF080837. Thomas A Ostler (TAO) gratefully acknowledges the support of the Marie Curie incoming BeIPD-COFUND fellowship program at the University of Liège. Ramon Cuadrado (RC) acknowledges the funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodoswa-Curie grant agreement No. 665919. ICN2 is supported by the Severo Ochoa program from Spanish MINECO (Grant No. SEV-2013-0295). László Oroszlány (LO) and László Szunyogh (LS) are grateful for the support by the Hungarian National Scientific Research Fund (NKFIH) under project Nos. K115575, K108676, K115608 and FK124723. L. O. also acknowledges support from the Janos Bolyai Scholarship of the Hungarian Academy of Sciences as well as the National Quantum Technologies Program 2017-1.2.1-NKP-2017-00001 of the NRDI Office of Hungary. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 737093, FEMTOTERABYTE as well as the financial support of the Advanced Storage Technology Consortium and Seagate Technology.