Giant localised spin-Peltier effect due to ultrafast domain wall motion in antiferromagnetic metals

AbstractSpin thermo-electric phenomena have attracted wide attention recently, e.g., the spin Peltier effect—heat generation by magnonic spin currents. Here, we find that the spin Peltier effect also manifests as a heat wave accompanying fast moving magnetic textures. High speed and extreme magnetic excitation localisation are paramount for efficient transfer of energy from the spin-degrees of freedom to electrons and lattice. While satisfying both conditions is subject to severe restrictions in ferromagnets, we find that domain walls in antiferromagnets can overcome these limitations due to their ultrahigh mobility and ultra-small widths originating from the relativistic contraction. To illustrate our findings, we show that electric current driven domain wall motion in the antiferromagnetic metal Mn2Au can carry a localised heat wave with temperature up to 1 K. Since domain walls are localised magnetic objects, this effect has the potential for nanoscale heating sensing and functionalities.</jats:p

Giant localised spin-Peltier effect due to ultrafast domain wall motion in antiferromagnetic metals

AbstractSpin thermo-electric phenomena have attracted wide attention recently, e.g., the spin Peltier effect—heat generation by magnonic spin currents. Here, we find that the spin Peltier effect also manifests as a heat wave accompanying fast moving magnetic textures. High speed and extreme magnetic excitation localisation are paramount for efficient transfer of energy from the spin-degrees of freedom to electrons and lattice. While satisfying both conditions is subject to severe restrictions in ferromagnets, we find that domain walls in antiferromagnets can overcome these limitations due to their ultrahigh mobility and ultra-small widths originating from the relativistic contraction. To illustrate our findings, we show that electric current driven domain wall motion in the antiferromagnetic metal Mn2Au can carry a localised heat wave with temperature up to 1 K. Since domain walls are localised magnetic objects, this effect has the potential for nanoscale heating sensing and functionalities.</jats:p

Inertial displacement of a domain wall excited by ultra-short circularly polarized laser pulses.

Domain wall motion driven by ultra-short laser pulses is a pre-requisite for envisaged low-power spintronics combining storage of information in magnetoelectronic devices with high speed and long distance transmission of information encoded in circularly polarized light. Here we demonstrate the conversion of the circular polarization of incident femtosecond laser pulses into inertial displacement of a domain wall in a ferromagnetic semiconductor. In our study, we combine electrical measurements and magneto-optical imaging of the domain wall displacement with micromagnetic simulations. The optical spin-transfer torque acts over a picosecond recombination time of the spin-polarized photo-carriers that only leads to a deformation of the initial domain wall structure. We show that subsequent depinning and micrometre-distance displacement without an applied magnetic field or any other external stimuli can only occur due to the inertia of the domain wall

Nanocontact size dependence of the properties of vortex-based spin torque oscillators

We study the frequency, linewidth, and power of spin torque driven vortex oscillators, based on a nanocontacted spin-valve (SV). The oscillation frequency strongly decreases with the contact size, and increases with the current. The power delivered by the oscillator is not quadratic with the current, in contrast with the behavior expected from the rigid vortex model (RVM). The linewidth is almost independent of the current at low current and does not strongly depend on the nanocontact size. We compare our findings with the outcomes of the RVM. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheimstatus: publishe

Antiferromagnetic domain wall memory with neuromorphic functionality

Acknowledgements: This work was supported in part by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) through Project-ID 314695032 – SFB 1277 (Subprojects A010) “Emergente relativistische Effekte in der Kondensierten Materie”, Project-ID452301518 “Investigation of quench switching of antiferromagnets with high spatial and temporal resolution” and by the European Union’s Horizon 2020 research and innovation program under the Marie Sk lodowska- Curie Grant Agreement No. 861300 “Cold Opto-Magnetism for Random Access Devices”. The work had also the support from the Czech Science Foundation within the Project GACR 21-28876J.AbstractAntiferromagnetic materials have unique properties due to their alternating spin arrangements. Their compensated magnetic order, robust against external magnetic fields, prevents long-distance crosstalk from stray fields. Furthermore, antiferromagnets with combined parity and time-reversal symmetry enable electrical control and detection of ultrafast exchange-field enhanced spin manipulation up to THz frequencies. Here we report the experimental realization of a nonvolatile antiferromagnetic memory mimicking an artificial synapse, in which the reconfigurable synaptic weight is encoded in the ratio between reversed antiferromagnetic domains. The non-volatile memory is “written” by spin-orbit torque-driven antiferromagnetic domain wall motion and “read” by nonlinear magnetotransport. We show that the absence of long-range interacting stray magnetic fields leads to very reproducible electrical pulse-driven variations of the synaptic weights.</jats:p

Ultrafast antiferromagnetic switching of Mn<inf>2</inf>Au with laser-induced optical torques

Acknowledgements: The authors acknowledge funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie International Training Network COMRAD (grant agreement No 861300). The atomistic simulations were undertaken on the VIKING cluster, which is a high performance compute facility provided by the University of York. F.F. and Y.M. acknowledge the funding by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) − TRR 173/2 − 268565370 (project A11) and Sino-German research project DISTOMAT (MO 1731/10-1) of the DFG. The work of O.C.-F. has been supported by DFG via CRC/TRR 227, project ID 328545488 (Project MF).AbstractUltrafast manipulation of the Néel vector in metallic antiferromagnets most commonly occurs by generation of spin-orbit (SOT) or spin-transfer (STT) torques. Here, we predict another possibility for antiferromagnetic domain switching by using novel laser optical torques (LOTs). We present results of atomistic spin dynamics simulations from the application of LOTs for all-optical switching of the Néel vector in the antiferromagnet Mn2Au. The driving mechanism takes advantage of the sizeable exchange enhancement, characteristic of antiferromagnetic dynamics, allowing for picosecond 90 and 180-degree precessional toggle switching of the Néel vector with laser fluences on the order of mJ/cm2. A special symmetry of these novel torques greatly minimises the over-shooting effect common to precessional spin switching by SOT and STT methods. We demonstrate the opportunity for LOTs to produce deterministic, non-toggle switching of single antiferromagnetic domains. Lastly, we show that even with sizeable ultrafast heating by laser in metallic systems, there exist a large interval of laser parameters where the LOT-assisted toggle and preferential switchings in magnetic grains have probabilities close to one. The proposed protocol could be used on its own for all-optical control of antiferromagnets for computing or memory storage, or in combination with other switching methods to lower energy barriers and/or to prevent over-shooting of the Néel vector.</jats:p

Microglia‐leucocyte axis in cerebral ischaemia and inflammation in the developing brain

Development of the Central Nervous System (CNS) is reliant on the proper function of numerous intricately orchestrated mechanisms that mature independently, including constant communication between the CNS and the peripheral immune system. This review summarizes experimental knowledge of how cerebral ischaemia in infants and children alters physiological communication between leucocytes, brain immune cells, microglia and the neurovascular unit (NVU)-the "microglia-leucocyte axis"-and contributes to acute and long-term brain injury. We outline physiological development of CNS barriers in relation to microglial and leucocyte maturation and the plethora of mechanisms by which microglia and peripheral leucocytes communicate during postnatal period, including receptor-mediated and intracellular inflammatory signalling, lipids, soluble factors and extracellular vesicles. We focus on the "microglia-leucocyte axis" in rodent models of most common ischaemic brain diseases in the at-term infants, hypoxic-ischaemic encephalopathy (HIE) and focal arterial stroke and discuss commonalities and distinctions of immune-neurovascular mechanisms in neonatal and childhood stroke compared to stroke in adults. Given that hypoxic and ischaemic brain damage involve Toll-like receptor (TLR) activation, we discuss the modulatory role of viral and bacterial TLR2/3/4-mediated infection in HIE, perinatal and childhood stroke. Furthermore, we provide perspective of the dynamics and contribution of the axis in cerebral ischaemia depending on the CNS maturational stage at the time of insult, and modulation independently and in consort by individual axis components and in a sex dependent ways. Improved understanding on how to modify crosstalk between microglia and leucocytes will aid in developing age-appropriate therapies for infants and children who suffered cerebral ischaemia