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Antiferromagnets can encode information in their ordered magnetic structure, providing the basis for future spintronic devices1–3. The control and understanding of antiferromagnetic domain walls, which are the interfaces between domains with differing order parameter orientations, are key ingredients for advancing antiferromagnetic spintronic technologies. However, studies of the intrinsic mechanics of individual antiferromagnetic domain walls are difficult because they require sufficiently pure materials and suitable experimental approaches to address domain walls on the nanoscale. Here we nucleate isolated 180° domain walls in a single crystal of Cr2O3, a prototypical collinear magnetoelectric antiferromagnet, and study their interaction with topographic features fabricated on the sample. We demonstrate domain wall manipulation through the resulting engineered energy landscape and show that the observed interaction is governed by the surface energy of the domain wall. We propose a topographically defined memory architecture based on antiferromagnetic domain walls. Our results advance the understanding of domain wall mechanics in antiferromagnets.High-resolution magnetometry shows that the shape of domain walls in Cr2O3 is determined by the energetic cost of their surface area. The walls behave like elastic surfaces that avoid thicker parts of the sample where they would need to be larger.

Antiferromagnetic insulators are a prospective materials platform for magnonics, spin superfluidity, THz spintronics, and non-volatile data storage. A magnetomechanical coupling in antiferromagnets offers vast advantages in the control and manipulation of the primary order parameter yet remains largely unexplored. Here, we discover a new member in the family of flexoeffects in thin films of Cr 2 O 3 . We demonstrate that a gradient of mechanical strain can impact the magnetic phase transition resulting in the distribution of the Néel temperature along the thickness of a 50-nm-thick film. The inhomogeneous reduction of the antiferromagnetic order parameter induces a flexomagnetic coefficient of about 15  μ B  nm −2 . The antiferromagnetic ordering in the inhomogeneously strained films can persist up to 100 °C, rendering Cr 2 O 3 relevant for industrial electronics applications. Strain gradient in Cr 2 O 3 thin films enables fundamental research on magnetomechanics and thermodynamics of antiferromagnetic solitons, spin waves and artificial spin ice systems in magnetic materials with continuously graded parameters. Flexomagnetism refers to the modification of the magnetic properties of a material due to inhomogeneous strain, and offers a promising pathway to the control and manipulation of magnetism. Here, Makushko et al. explore flexomagnetism in antiferromagnetic thin films of Cr 2 O 3 , demonstrating a gradient of the Néel temperature as a result of an inhomogeneous strain.

Recirculating aquaculture system (RAS) technology is seen worldwide as a solution for sustainable fish production. However, there are still deficiencies in the process technology imperiling consistent operation and thus economic results. Drawbacks are linked to essential processes of the water treatment systems such as denitrification. Nitrogenous waste needs to be removed from RAS process water to maintain an adequate production environment for fish and to mitigate the environmental impact of discharged process water. At present, denitrification lacks reliable process control, especially regarding the organic carbon feed to heterotrophic denitrification processes. An investigation into heterotrophic denitrification in an experimental RAS resulted in the discovery of a virtual sensor based on measurements of the oxidation reduction potential (ORP). The virtual sensor responds to an insufficient carbon feed to denitrification. It is based on the oxidation of nitrite in an ozone-enhanced foam flotation installed downstream of the denitrification. The sensor essentially delivers a binary signal denoting either a complete or an incomplete denitrification process. The virtual sensor can be used for reliably controlling heterotrophic denitrification. It requires an upgraded process chain employing ozone-enhanced foam flotation (protein skimmer) downstream of the denitrification. However, the virtual sensor does not require any additional instrumentation.

Antiferromagnetic spin textures, compared to their ferromagnetic counterparts, innately possess high stability with respect to external disturbance and high-frequency dynamics compatible with ultrafast information processing. However, deterministic creation and reconfigurable switching of different antiferromagnetic spin textures have not been realized. Here, we demonstrate room-temperature deterministic switching between three antiferromagnetic textures identified by characteristically different high frequency dynamics in single-crystal hematite (α-Fe2O3). All three states are found to be remarkably stable and fully controllable, as confirmed by 1000 switching cycles and spatially resolved spectroscopy and they may be created by local magnetization switching in the nonlinear excitation regime. The switching to the following stable state requires only one microwave pulse (100 ns) with ultralow energy consumption (1 nJ). Our Brillouin light scattering (BLS) microscopy data reinforces that the detected magnon modes are associated to excitations of domain walls and circular spin textures. The progressive switching between the three distinct states imitates the weighted sum operation in neuromorphic computing, suggesting the possibility of using spin textures in antiferromagnets for information processing. Spin-waves have a variety of advantages for information processing, and here, Chen, Xu and coauthors demonstrate the deterministic switching of antiferromagnetic spin textures using non-linear spin-waves. The switching process is progressive, mirroring weighted sum operations in neuromorphic computing.

Magnons can transfer information in metals and insulators without Joule heating, and therefore are promising for low-power computation. The on-chip magnonics however suffers from high losses due to limited magnon decay length. In metallic thin films, it is typically on the tens of micrometre length scale. Here, we demonstrate an ultra-long magnon decay length of up to one millimetre in multiferroic/ferromagnetic BiFeO 3 (BFO)/La 0.67 Sr 0.33 MnO 3 (LSMO) heterostructures at room temperature. This decay length is attributed to a magnon-phonon hybridization and is more than two orders of magnitude longer than that of bare metallic LSMO. The long-distance modes have high group velocities of 2.5 km s −1 as detected by time-resolved Brillouin light scattering. Numerical simulations suggest that magnetoelastic coupling via the BFO/LSMO interface hybridizes phonons in BFO with magnons in LSMO to form magnon-polarons. Our results provide a solution to the long-standing issue on magnon decay lengths in metallic magnets and advance the bourgeoning field of hybrid magnonics. Long-distance magnon transport is highly desired for magnonics. Here, the authors demonstrate a millimetre-long magnon decay length in multiferroic heterostructures, which is attributed to magnon-polarons induced by the magnetoelastic coupling.

We present a study on nanoscale skyrmionic spin textures in , a rare-earth complex noncollinear ferromagnet. We confirm, using X-ray microscopy, that can host lattices of metastable skyrmion bubbles at room temperature in the absence of a magnetic field, after applying a suitable field cooling protocol. The skyrmion bubbles are robust against temperature changes from room temperature to 330 K. Furthermore, the skyrmion bubbles can be distorted, deformed, and recovered by varying strength and orientation of the applied magnetic field. We have used nitrogen-vacancy nanoscale magnetic imaging to estimate and map the magnetic stray fields originating from our lamella samples and find stray field magnitudes on the order of a few mT near the sample surface. Micromagnetic simulations show an overall agreement with the observed behaviour of the sample under different magnetic field protocols. We also find that the presence of the Dzyaloshinskii-Moriya interaction is not required to reproduce our experimental results. Its inclusion in the simulation leads to a reversal of the skyrmionic object core polarity, which is not experimentally observed. Our results further corroborate the stability and robustness of the skyrmion bubbles formed in and their potential for future spintronic applications.

Spin Hall oscillators (SHO) are promising candidates for the generation, detection and amplification of high frequency signals, that are tunable through a wide range of operating frequencies. They offer to be read out electrically, magnetically and optically in combination with a simple bilayer design. Here, we experimentally study the spatial dependence and spectral properties of auto-oscillations in SHO devices based on Pt(7 nm)/Ni 80 Fe 20 (5 nm) tapered nanowires. Using Brillouin light scattering microscopy, we observe two individual self-localized spin-wave bullets that oscillate at two distinct frequencies (5.2 GHz and 5.45 GHz) and are localized at different positions separated by about 750 nm within the SHO. This state of a tapered SHO has been predicted by a Ginzburg-Landau auto-oscillator model, but not yet been directly confirmed experimentally. We demonstrate that the observed bullets can be individually synchronized to external microwave signals, leading to a frequency entrainment, linewidth reduction and increase in oscillation amplitude for the bullet that is selected by the microwave frequency. At the same time, the amplitude of other parasitic modes decreases, which promotes the single-mode operation of the SHO. Finally, the synchronization of the spin-wave bullets is studied as a function of the microwave power. We believe that our findings promote the realization of extended spin Hall oscillators accomodating several distinct spin-wave bullets, that jointly cover an extended range of tunability.

This study examined the performance of three independently operated denitrifying moving bed biofilm reactors (MBBRs) in a zero-exchange marine recirculating aquaculture system (RAS) stocked with European seabass (Dicentrarchus labrax). A semi-automated control strategy was applied to foster spontaneous denitrification. Process automation consisted of a pulsed carbon supply and an inflow of nitrate-rich, aerated process water controlled by the oxidation-reduction potential (ORP) in the MBBR. Carbon dosing frequency was adjusted manually if the process produced unwanted products (i.e., nitrite or ammonia). OPR-controlled inflow stimulated bacterial activities in the MBBRs until inflow reached the pre-set maximum at a hydraulic retention time (HRT) of 0.75 h. This allowed for a quick start-up of the denitrification processes in spite of high initial variability of process water inflow and of nitrate removal efficiency (NRE). A start-up with glycerol did not induce a stable denitrification process; however, after the process had been established with acetate, glycerol promoted efficient denitrification with NRE close to one. The successive application of the two carbon sources resulted in a high nitrate removal rate (NRR) of 2 kg nitrate-N m−3 day−1 in the biofilters. This diminished the concentration of nitrate-nitrogen (nitrate-N) in the RAS (volume 9 m3) from 176 to 36 g m−3 in 42 days with biofilters comprising only 1% of the RAS volume. The implications for the development of an automated denitrification process are discussed.

A Correction to this paper has been published: https://doi.org/10.1038/s41567-021-01205-3.

Despite numerous efforts, drug based treatments for patients suffering from lung cancer remains poor. As a promising alternative, we investigated the therapeutic potential of BC-819 for the treatment of lung cancer in mouse tumor models. BC-819 is a novel plasmid DNA which encodes for the A-fragment of Diphtheria toxin and has previously been shown to successfully inhibit tumor growth in human clinical study of bladder carcinoma. In a first set of experiments, we examined in vitro efficacy of BC-819 in human lung cancer cell-lines NCI-H460, NCI-H358 and A549, which revealed >90% reduction of cell growth. In vivo efficacy was examined in an orthotopic mouse xenograft lung cancer model and in a lung metastasis model using luminescent A549-C8-luc adenocarcinoma cells. These cells resulted in peri- and intra-bronchiolar tumors upon intrabronchial application and parenchymal tumors upon intravenous injection, respectively. Mice suffering from these lung tumors were treated with BC-819, complexed to branched polyethylenimine (PEI) and aerosolized to the mice once per week for a period of 10 weeks. Using this regimen, growth of intrabronchially induced lung tumors was significantly inhibited (p = 0.01), whereas no effect could be observed in mice suffering from lung metastasis. In summary, we suggest that aerosolized PEI/BC-819 is capable of reducing growth only in tumors arising from the luminal part of the airways and are therefore directly accessible for inhaled BC-819.