Antiferromagnetic (AFM) skyrmions are envisioned as ideal localized topological magnetic bits in future information technologies. In contrast to ferromagnetic (FM) skyrmions, they are immune to the skyrmion Hall effect, might offer potential terahertz dynamics while being insensitive to external magnetic fields and dipolar interactions. Although observed in synthetic AFM structures and as complex meronic textures in intrinsic AFM bulk materials, their realization in non-synthetic AFM films, of crucial importance in racetrack concepts, has been elusive. Here, we unveil their presence in a row-wise AFM Cr film deposited on PdFe bilayer grown on fcc Ir(111) surface. Using first principles, we demonstrate the emergence of single and strikingly interpenetrating chains of AFM skyrmions, which can co-exist with the rich inhomogeneous exchange field, including that of FM skyrmions, hosted by PdFe. Besides the identification of an ideal platform of materials for intrinsic AFM skyrmions, we anticipate the uncovered knotted solitons to be promising building blocks in AFM spintronics.

We analyze an electron-hole asymmetry model for simultaneous two-state operation in semiconductor quantum dot lasers. From the linearized equations, we determine simple analytical expressions for the relaxation oscillation (RO) frequencies. Of particular interest is the fact that different expressions for the RO frequencies are obtained depending on the relative values of the photon lifetime and the basic time scale of the nonlinear intradot interaction. If comparable, we find only one frequency that depends on a combination of the two-state intensities.

Nuclear spins are among the potential candidates prospected for quantum information technology. A recent breakthrough enabled to atomically resolve their interaction with the electron spin, the so-called hyperfine interaction, within individual atoms utilizing scanning tunneling microscopy (STM). Intriguingly, this was only realized for a few species put on a two-layers thick MgO. Here, we systematically quantify from first-principles the hyperfine interactions of the whole series of 3d transition adatoms deposited on various thicknesses of MgO, NaF, NaCl, h–BN, and Cu2N films. We identify the adatom-substrate complexes with the largest hyperfine interactions and unveil the main trends and exceptions. We reveal the core mechanisms at play, such as the interplay of the local bonding geometry and the chemical nature of the thin films, which trigger transitions between high- and low-spin states accompanied with subtle internal rearrangements of the magnetic electrons. By providing a general map of hyperfine interactions, our work has immediate implications in future STM investigations aiming at detecting and realizing quantum concepts hinging on nuclear spins.

Skyrmions are prospected as the potential future of data storage due to their topologically protected spin structures. However, traditional ferromagnetic (FM) skyrmions experience deflection when driven with an electric current, hindering their usage in spintronics. Antiferromagnetic (AFM) skyrmions, consisting of two FM solitons coupled antiferromagnetically, are predicted to have zero Magnus force, making them promising candidates for spintronic racetrack memories. Currently, they have been stabilized in synthetic AFM structures, i.e., multilayers hosting FM skyrmions, which couple antiferromagnetically through a non-magnetic spacer, while recent first-principle simulations predict their emergence in an intrinsic form, within a row-wise AFM single monolayer of Cr deposited on a PdFe bilayer grown on Ir (111) surfaces. The latter material forms a triangular lattice, where single and interlinked AFM skyrmions can be stabilized. Here, we explore the minimal Heisenberg model, enabling the occurrence of such AFM solitons and the underlying phase diagrams by accounting for the interplay between the Dzyaloshinskii–Moriya and Heisenberg exchange interactions, as well as the magnetic anisotropy and impact of the magnetic field. By providing the fundamental basis to identify and understand the behavior of intrinsic AFM skyrmions, we anticipate our model to become a powerful tool for exploring and designing new topological magnetic materials to conceptualize devices for AFM spintronics.