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Magnetoelastic effects in antiferromagnetic CuMnAs are investigated by applying dynamic strain in the 0.01% range through surface acoustic waves in the GaAs substrate. The magnetic state of the CuMnAs/GaAs is characterized by a multitude of submicron-sized domains which we image by x-ray magnetic linear dichroism combined with photoemission electron microscopy. Within the explored strain range, CuMnAs shows magnetoelastic effects in the form of N\'eel vector waves with micrometer wavelength, which corresponds to an averaged overall spin-axis rotation up to 2.4 deg driven by the time-dependent strain from the surface acoustic wave. Measurements at different temperatures indicate a reduction of the wave amplitude when lowering the temperature. However, no domain wall motion has been detected on the nanosecond timescale

Antiferromagnetic materials hold potential for use in spintronic devices with fast operation frequencies and field robustness. Despite the rapid progress in proof-of-principle functionality in recent years, there has been a notable lack of understanding of antiferromagnetic domain formation and manipulation, which translates to either incomplete or non-scalable control of the magnetic order. Here, we demonstrate simple and functional ways of influencing the domain structure in CuMnAs and Mn2Au, two key materials of antiferromagnetic spintronics research, using device patterning and strain engineering. Comparing x-ray microscopy data from two different materials, we reveal the key parameters dictating domain formation in antiferromagnetic devices and show how the non-trivial interaction of magnetostriction, substrate clamping and edge anisotropy leads to specific equilibrium domain configurations. More specifically, we observe that patterned edges have a significant impact on the magnetic anisotropy and domain structure over long distances, and we propose a theoretical model that relates short-range edge anisotropy and long-range magnetoelastic interactions. The principles invoked are of general applicability to the domain formation and engineering in antiferromagnetic thin films at large, which will pave the way towards realizing truly functional antiferromagnetic devices., Comment: 31 pages, 7 figures

We describe measurements of the uniaxial magnetic anisotropy and spin-flop rotation of the N\'eel vector in antiferromagnetic CuMnAs thin films using neutron diffraction. The suppression of the magnetic (100) peak under magnetic fields is observed for films as thin as 20 nm indicating that they undergo a spin-flop transition. Good agreement is found between neutron diffraction and electron transport measurements of the spin-flop rotation in the same layer, with a similar shape and hysteresis of the obtained curves, while the neutron measurements provide a quantitative determination of the spin flop extent throughout the antiferromagnet layer., Comment: 5 pages, 4 figures, includes supplementary information

Tetragonal CuMnAs is a room temperature antiferromagnet with an electrically reorientable N\'eel vector and a Dirac semimetal candidate. Direct measurements of the electronic structure of single-crystalline thin films of tetragonal CuMnAs using angle-resolved photoemission spectroscopy (ARPES) are reported, including Fermi surfaces (FS) and energy-wavevector dispersions. After correcting for a chemical potential shift of $\approx-390$ meV (hole doping), there is excellent agreement of FS, orbital character of bands, and Fermi velocities between the experiment and density functional theory calculations. Additionally, 2x1 surface reconstructions are found in the low energy electron diffraction (LEED) and ARPES. This work underscores the need to control the chemical potential in tetragonal CuMnAs to enable the exploration and exploitation of the Dirac fermions with tunable masses, which are predicted to be above the chemical potential in the present samples., Comment: Submitted to Physical Review X. 20 pages. 9 figures

Efficient manipulation of antiferromagnetic (AF) domains and domain walls has opened up new avenues of research towards ultrafast, high-density spintronic devices. AF domain structures are known to be sensitive to magnetoelastic effects, but the microscopic interplay of crystalline defects, strain and magnetic ordering remains largely unknown. Here, we reveal, using photoemission electron microscopy combined with scanning X-ray diffraction imaging and micromagnetic simulations, that the AF domain structure in CuMnAs thin films is dominated by nanoscale structural twin defects. We demonstrate that microtwin defects, which develop across the entire thickness of the film and terminate on the surface as characteristic lines, determine the location and orientation of 180 degree and 90 degree domain walls. The results emphasize the crucial role of nanoscale crystalline defects in determining the AF domains and domain walls, and provide a route to optimizing device performance.

The interest in understanding scaling limits of magnetic textures such as domain walls spans the entire field of magnetism from its relativistic quantum fundamentals to applications in information technologies. The traditional focus of the field on ferromagnets has recently started to shift towards antiferromagnets which offer a rich materials landscape and utility in ultra-fast and neuromorphic devices insensitive to magnetic field perturbations. Here we report the observation that domain walls in an epitaxial crystal of antiferromagnetic CuMnAs can be atomically sharp. We reveal this ultimate domain wall scaling limit using differential phase contrast imaging within aberrationcorrected scanning transmission electron microscopy, which we complement by X-ray magnetic dichroism microscopy and ab initio calculations. We highlight that the atomically sharp domain walls are outside the remits of established spin-Hamiltonian theories and can offer device functionalities unparalleled in ferromagnets., Comment: 8 pages, 4 figures, Supplementary information

Antiferromagnets offer spintronic device characteristics unparalleled in ferromagnets owing to their lack of stray fields, THz spin dynamics, and rich materials landscape. Microscopic imaging of aniferromagnetic domains is one of the key prerequisites for understading physical principles of the device operation. However, adapting common magnetometry techniques to the dipolar-field-free antiferromagnets has been a major challenge. Here we demonstrate in a collinear antiferromagnet a thermoelectric detection method by combining the magneto-Seebeck effect with local heat gradients generated by scanning far-field or near-field techniques. In a 20 nm epilayer of uniaxial CuMnAs we observe reversible 180 deg switching of the N\'eel vector via domain wall displacement, controlled by the polarity of the current pulses. We also image polarity-dependent 90 deg switching of the N\'eel vector in a thicker biaxial film, and domain shattering induced at higher pulse amplitudes. The antiferromagnetic domain maps obtained by our laboratory technique are compared to measurements by the established synchrotron microscopy using X-ray magnetic linear dichroism.

We present a detailed study of the growth of the tetragonal polymorph of antiferromagnetic CuMnAs by the molecular beam epitaxy technique. We explore the parameter space of growth conditions and their effect on the microstructural and transport properties of the material. We identify its typical structural defects and compare the properties of epitaxial CuMnAs layers grown on GaP, GaAs and Si substrates. Finally, we investigate the correlation between the crystalline quality of CuMnAs and its performance in terms of electrically induced resistance switching., Comment: 10 pages, 8 figures and supplementary material

Ultra-fast dynamics, insensitivity to external magnetic fields, or absence of magnetic stray fields are examples of properties that make antiferromagnets of potential use in the development of spintronic devices. Similar to their ferromagnetic counterparts, antiferromagnets can store information in the orientations of the collective magnetic order vector. However, also in analogy to ferromagnets, the readout magnetoresistivity signals in simple antiferromagnetic films have been weak and the extension of the electrical reorientation mechanism to optics has not been achieved. Here we report reversible and reproducible quenching of an antiferromagnetic CuMnAs film by either electrical or ultrashort optical pulses into nano-fragmented domain states. The resulting resistivity changes approach 20\% at room temperature, which is comparable to the giant magnetoresistance ratios in ferromagnetic multilayers. We also obtain a signal readout by optical reflectivity. The analog time-dependent switching and relaxation characteristics of our devices can mimic functionality of spiking neural network components.

Epitaxial thin films of CuMnAs have recently attracted attention due to their potential to host relativistic antiferromagnetic spintronics and exotic topological physics. Here we report on the structural and electronic properties of a tetragonal CuMnAs thin film studied using scanning tunneling microscopy (STM) and density functional theory (DFT). STM reveals a surface terminated by As atoms, with the expected semi-metallic behavior. An unexpected zigzag step edge surface reconstruction is observed with emerging electronic states below the Fermi energy. DFT calculations indicate that the step edge reconstruction can be attributed to an As deficiency that results in changes in the density of states of the remaining As atoms at the step edge. This understanding of the surface structure and step edges on the CuMnAs thin film will enable in-depth studies of its topological properties and magnetism.

Louis Neel pointed out in his Nobel lecture that while abundant and interesting from a theoretical viewpoint, antiferromagnets did not seem to have any applications. Indeed, the alternating directions of magnetic moments on individual atoms and the resulting zero net magnetization make antiferromagnets hard to control by tools common in ferromagnets. Remarkably, Neel in his lecture provides the key which, as we show here, allows us to control antiferromagnets by electrical means analogous to those which paved the way to the development of ferromagnetic spintronics applications. The key noted by Neel is the equivalence of antiferromagnets and ferromagnets for effects that are an even function of the magnetic moment. Based on even-in-moment relativistic transport phenomena, we demonstrate room-temperature electrical switching between two stable configurations combined with electrical read-out in antiferromagnetic CuMnAs thin film devices. Our magnetic memory is insensitive to and produces no magnetic field perturbations which illustrates the unique merits of antiferromagnets for spintronics., Comment: 16 pages, 4 figures