We describe how thermally induced spin fluctuations modify the electronic structures of two prototypical altermagnets, CrSb and MnTe, via application of the disordered local moment picture. For both materials, our self-consistent, ab initio calculations demonstrate that local magnetic moments persist on Cr and Mn atoms in their paramagnetic states, necessitating a spin-polarised description of the electronic structure even above the Néel temperature, $T_\mathrm{N}$. Moreover, Kramers' spin degeneracy, which is broken for both materials in their altermagnetic ground states, is shown to be smoothly restored - on the average - as the local moments thermally disorder. In metallic CrSb, this occurs at temperatures well below $T_\mathrm{N}$ and the signature effects of its altermagnetism are lost as the magnetic disorder induces heavy smearing of strongly dispersive electronic states around the Fermi energy. By contrast, in semiconducting MnTe, with its band gap largely unaffected by magnetic disorder, the spin degeneracy only returns at temperatures close to and above $T_\mathrm{N}$. We quantify the temperature dependence of the altermagnetic order parameter and the underlying electronic structures of both materials, with significant implications for their spin transport properties.

We investigate the spin dynamics of the non-collinear kagome triangular anti-ferromagnets Mn$_3$Rh using linear response time-dependent density functional theory. To this end, we present a novel first principles approach relying on the evaluation of dynamical susceptibility based on the non-collinear KKR Green's functions method. This approach enables us not only to treat spin and charge dynamics on an equal footing but also address the Landau damping of spin waves being inaccessible to adiabatic methods. Our calculations reveal three distinct Goldstone modes dispersing linearly in the long-wavelength regime. We discuss their non-trivial polarizations and proceed to an in-depth analysis of their Landau damping. The spin-waves turn out to be defined in the whole Brillouin zone but their damping become substantial away from the zone's center.

Magnetic tunnel junctions (MTJs), a key spintronic device, have shown rapid development recently using two-dimensional (2D) magnets. In particular, MTJs formed from twisted 2D antiferromagnets (AFMs) push nonvolatile magnetic information storage to the atomic limit. Here we demonstrate 2D twisted MTJs with multiple distinct nonvolatile states. Asymmetric MTJ structures formed by twisting a single ferromagnetic CrSBr monolayer and a single antiferromagnetic CrSBr bilayer exhibit two distinct states with up to 700% tunneling magnetoresistance in zero magnetic field at 2 K. By adding a second CrSBr monolayer to form a second twisted interface, four nonvolatile states can be accessed in zero magnetic field. More importantly, any one state among the four states can be switched to any other using magnetic fields. We further demonstrate all-antiferromagnetic MTJs with three twisted antiferromagnetic CrSBr bilayers that exhibit multiple nonvolatile states. Our work shows that it is possible to store multiple-state magnetic information in a single device by integrating several twisted interfaces in the atomic limit.

Harnessing symmetry-protected terahertz Dirac magnons would enable robust, low-loss magnonic transport, offering a compelling alternative to conventional information carriers. Here we propose a novel yet remarkably simple platform for hosting terahertz Dirac magnons in low-dimensional magnetic architectures. We demonstrate, through first-principles calculations and linear spin-wave theory, that atomically designed magnetic layers possessing C3v symmetry can exhibit Dirac magnon band crossings and a quantized Berry phase of ±π. The formation of the Dirac point, absent in their bulk counterpart, is a direct consequence of the reduced dimensionality. Our finding not only highlights the unique dimensionality-driven Dirac magnons in layered structures but also sheds light on the complex behavior of the Berry phase in such structures. We show that parameters such as surface symmetry, atomic layer composition, film thickness, epitaxial relationship, and chemical environment can be used to tune the Berry phase and the resulting symmetry-associated properties.

Noncollinear spin structures have attracted tremendous attention because they offer a versatile platform for spin control and manipulation, essential in spintronics. Realizing noncollinearity in ferrimagnetic insulators is of particular interest as they can be potentially utilized in low-damping spintronics with tunable magnetic order. Within the spinel-ferrite family, Zn and Al-substituted nickel ferrite (NiZAF) has emerged as an excellent choice for low-damping spintronics. However, realizing noncollinearity in such systems remains challenging. Here, we present evidence of noncollinear spin structure in the NiZAF thin films induced by the rare earth Dy-doping, utilizing the soft x-ray spectroscopy methods such as magnetic circular dichroism and x-ray resonant magnetic reflectivity (XRMR). In particular, XRMR reveals a spiral-type spin structure, which is attributed to the Dzyaloshinskii-Moriya interaction, arising due to broken inversion symmetry by the Dy-induced local strain field as confirmed by our theoretical calculations. The realization of noncollinearity in the spinel-ferrite opens pathway to explore the possibility of chiral magnetic domains and topological spin textures exhibiting promise for oxide-based spintronics

A distinct difference between graphene—an atomic layer of carbon—and conventional semiconductors is that its electrons behave as massless Dirac fermions, giving rise to unprecedented physical properties. Magnetically ordered solids host magnons, quasiparticles associated with magnetic degrees of freedom. While Dirac magnons have recently been predicted in specific insulating or rare-earth magnets, their existence in thin 3d magnets remains elusive because of the complex nature of itinerant magnetism and dimensionality effects. Here, we demonstrate the presence of Dirac magnons in a thin itinerant elemental ferromagnet. By investigating atomically designed hexagonal close-packed cobalt films, we establish that magnons in such structures resemble the Dirac electrons in graphene. We explain the physical nature of these Dirac magnons and discuss the consequences of symmetry, dimensionality, magnetic interactions, the number of atomic layers, and cobalt’s itinerant magnetism on the properties of the Dirac points. Our results pave the way for finding and engineering Dirac magnons in a variety of low-dimensional layered 3d ferromagnets and metamaterials.

Heusler compounds constitute a large family of intermetallic materials notable for their wide variety of properties such as magnetism, multi-ferroicity, nontrivial band topology, superconductivity and so on. Among their magnetic properties one finds a tremendous variety of states from simple ferromagnetism to skyrmion crystals. In most Mn _2 -based Heuslers the magnetism is typically collinear. An exception is Mn _2 RhSn in which an unusual ground state with magnetic canting and a temperature-induced spin re-orientation into the collinear ferrimagnetic phase has been reported from experiments. In this work, we employ first-principles calculations and the classical Heisenberg model simulations to provide a simple account of the unusual phase diagram in this magnet. We also highlight Weyl points in the computed band structure of Mn _2 RhSn and the resulting Fermi arcs.

Abstract A wide variety of chiral non-collinear spin textures have been discovered and have unique properties that make them highly interesting for technological applications. However, many of these are found in complex materials and only in a narrow window of temperature. Here, we show the formation of Néel-type skyrmions in thin layers of simple ferromagnetic alloys, namely Co-Al and Co-Ni-Al, over a wide range of temperature up to ~773 K, by imposing a strain gradient perpendicular to the sample plane via epitaxy with an Ir-Al underlayer. The Néel skyrmions are directly observed using Lorentz transmission electron microscopy in freestanding membranes at high temperatures and the strain gradient is directly measured from x-ray diffraction asymmetric peak profiles. Our concept allows for simple centrosymmetric ferromagnets with high magnetic ordering temperatures to exhibit skyrmions at temperatures well above room temperature, thereby, bringing closer skyrmionic electronics.

A novel implementation of the linear response time-dependent density functional theory addressing spin excitations in non-collinear magnets based on the Korringa-Kohn-Rostoker Green's function method is presented. Following the exposition of the formalism based on the adiabatic local spin density approximation to the exchange-correlation kernel generalized to the non-collinear case, the computational scheme is discussed in detail. The formation of the Goldstone modes in non-collinear susceptibility calculations is elaborated on formally and from the numerical convergence point of view. The scheme is deployed to study the dispersion, Landau damping, and spatial shapes of magnons for the representative members of the kagome non-collinear antiferromagnets.

A magnetic field typically suppresses superconductivity by either breaking Cooper pairs via the Zeeman effect or inducing vortex formation. However, under certain circumstances, a magnetic field can stabilize superconductivity instead. This seemingly counterintuitive phenomenon is associated with magnetic interactions and has been extensively studied in three-dimensional materials. By contrast, this phenomenon, hinting at unconventional superconductivity, remains largely unexplored in two-dimensional systems, with moiré-patterned graphene being the only known example. Here, we report the observation of reentrant superconductivity at the epitaxial (110)-oriented LaTiO 3 -KTaO 3 interface. This phenomenon occurs across a wide range of charge carrier densities, which, unlike in three-dimensional materials, can be tuned in situ via electrostatic gating. We propose that the observed reentrant superconductivity can arise from an interplay between strong spin-orbit coupling and a magnetic field–driven modification of the Fermi surface. Our findings provide insight into reentrant superconductivity and establish a robust platform for exploring unconventional superconducting phenomena in two-dimensional systems.

Using density functional theory, we characterize crystal and electronic structures as well as the topology of the XSb4Te4 family of materials (X =Ge, Sn, Pb) that are composed of the XSb2Te4 septuple layers interleaved by Sb bilayers. We first demonstrate that all these compounds are dynamically stable by means of phonon spectra calculations. Then, our electronic structure calculations, performed within the modified Becke-Johnson potential approximation, predict GeSb4Te(4) and SnSb4Te(4) to be semimetals, while PbSb4Te4 to be an insulator with a narrow gap of about 50 meV. Further, we find all XSb4Te4 to show both the strong Z(2) topology and the crystalline topology provided by the time-reversal and mirror reflection symmetries, respectively. We demonstrate the stability of this dual topological nature with respect to a considerable X-Sb intermixing previously found experimentally.

Studying and understanding many-body interactions, particularly electron-boson interactions, is essential for a deeper elucidation of fundamental physical phenomena and the development of novel material functionalities. Here, this aspect is explored in the weak itinerant ferromagnet LaCo2P2 by means of momentum-resolved photoelectron spectroscopy (ARPES) and first-principles calculations. The detailed ARPES patterns enable to unveil bulk and surface bands, spin splittings due to Rashba and exchange interactions, as well as the evolution of bands with temperature, which altogether creates a solid foundation for theoretical studies. The latter has allowed to establish the impact of electron-boson interactions on the electronic structure, that are reflected in its strong renormalization driven by electron-magnon interaction and the emergence of distinctive kinks of surface and bulk electron bands due to significant electron-phonon coupling. Our results highlight the distinct impact of electron-boson interactions on the electronic structure, particularly on the itinerant d states. Similar electronic states are observed in the isostructural iron pnictides, where electron-boson interactions play a crucial role in the emergence of superconductivity. It is believed that further studies of material systems involving both magnetically active d- and f-sublattices will reveal more advanced phenomena in the bulk and at distinct surfaces, driven by a combination of factors including Rashba and Kondo effects, exchange magnetism, and electron-boson interactions.

We report the emergence of two-dimensional itinerant half-metallicity in a two-atomic-layer thick iron-palladium alloy. Against the common belief that spin-orbit coupling is adverse to half-metallicity, the complex interplay between exchange and spin-orbit coupling counterintuitively enables it via electronic band hybridization. The 2D ferromagnet is engineered directly via controlled alloying and is verified experimentally via spin-resolved band structure analyses. First-principles calculations corroborate its tunability by providing a systematic bottom-up approach through stepwise ground-state construction. The appearance of hybridization points at specific k points, via interplay between exchange and spin-orbit interactions, is responsible for the emergence of half-metallicity.

Magnetic properties of crystalline solids are fundamental to a wide range of applications, capturing the attention of a vast scientific community. Thus, engineering magnetic order in materials such as ferromagnetism and antiferromagnetism holds great scientific and technological interest. Defects such as vacancies, interstitials, and dopants induce local perturbations within the crystal lattice. These perturbations locally disturb the entire symmetry of crystals, resulting in symmetry breaking. Oxides, in particular, exhibit intriguing properties when subjected to defects, which can lead to significant modifications in their structural, electronic, and magnetic properties. Such defects in non-magnetic oxides can induce magnetic symmetry breaking, leading to the formation of emergent magnetic domains and orderings. In this review, we focus on the recent progress in magnetic breaking symmetries in materials via defect engineering and present our perspectives on how these may lead to new understanding and applications.

Freestanding strongly correlated complex oxide thin films hold great potential in next-generation electronic and energy applications. Their high integrability and tunable properties may surpass those in bulk or epitaxial films. Water-assisted lift-off method is widely used to produce single-crystalline complex oxide membranes. It involves utilizing water-soluble sacrificial oxides such as Sr3Al2O6 (SAO), incorporated during multilayer growth. A key challenge is the incompatibility of direct growth between certain functional oxides (e.g., ferroics) and SAO, along with limited understanding of how film growth impacts both SAO dissolution and subsequent membrane quality. Here, we demonstrate how epitaxial strain engineering of SAO-based heterostructures, combined with overlying oxide layers (SrTiO3 and La0.7Sr0.3MnO3) grown via pulsed laser deposition, yields scalable, high-quality single-crystalline membranes through rapid, reproducible fabrication. Our findings reveal that the epitaxial strain of SAO layer is strongly affected by the subsequent growth condition (e.g., oxygen partial pressure) of upper oxide layers. Minimizing the strain relaxation of the SAO layer is crucial for both the layer-by-layer growth of upper oxide films and efficient dissolution dynamics of SAO. The use of a tetragonally strained SAO layer, remaining under oxygen-reduced conditions throughout the multilayer growth, allows for uniform and rapid (≤10 min) dissolution in water, producing millimeter-scale, microcrack-free, functional single-crystalline oxide membranes. This work provides key insights into how epitaxial growth affects membrane release and quality, providing a robust pathway for reliable, high-performance integration of freestanding oxide membranes using water-soluble layers.

We demonstrate atomic-scale mapping of local magnetic moments and doping effects in Ti-doped barium hexaferrite (BaFe11TiO19) using atom-sized electron vortex beams (EVBs) with controlled orbital angular momentum (OAM) in a scanning transmission electron microscope. By measuring electron energy loss magnetic circular dichroism (EMCD) at the Fe-L2,3 edges, we directly resolve the spatial distribution of antiparallel-aligned magnetic sublattices and quantify the impact of non-magnetic Ti4+ substitution. The EMCD signal, detected from single atomic Fe columns, reveals a marked reduction and sign reversal in the magnetic moment at Ti-rich 4f2 sites, corroborated by inelastic scattering simulations and density functional theory calculations that indicate induced Fe2+ formation and modified exchange interactions. Our results show that EVBs enable direct, element-specific, and atomically resolved magnetic characterization, opening new avenues for investigating local magnetic phenomena and dopant effects in nano-structured magnetic materials, such as those used in spintronic devices. This method paves the way for detailed studies of complex spin textures, magnetic interfaces, and dynamic processes at the atomic scale.

We study the ultrafast demagnetization dynamics of LnRh_2Si_2 (Ln = Pr, Nd, Sm, Gd, Tb, Dy, Ho) antiferromagnets (AFM) after excitation by a laser pulse, using a combination of density functional theory and atomistic spin and spin-lattice dynamics simulations. First, we calculate the Heisenberg interactions using the magnetic force theorem and compare two approaches, where the 4f states of the rare earths are treated as frozen core states or as valence states with added correlation corrections. We find marked quantitative differences in terms of predicted Curie temperature for most of the systems, especially for those with large orbital moment of the rare earth cations. This can be attributed to the importance of indirect interactions of the 4f states through the Si states, which depend on the binding energy of the 4f states and coexists with RKKY-type interactions mediated by the conduction states. However, qualitatively, both approaches agree in terms of the predicted AFM ordering at low temperatures. In the second step, the atomistic dynamics simulations are combined with a heat-conserving two-temperature model, allowing for the calculation of spin and electronic temperatures during the magnetization dynamics simulations. Despite quite different demagnetization times, magnetization dynamics of all studied LnRh_2Si_2 AFM exhibit similar two-step behavior, in particular, the first fast drop followed by slower demagnetization. We observe that the demagnetization amplitude depends linearly on laser fluence for low fluences, which is in agreement with experimental observations. We also investigate the impact of lattice dynamics on ultrafast demagnetization using coupled atomistic spin-lattice dynamics simulations and a heat-conserving three-temperature model, which confirm linear dependence of magnetisation on laser fluence.

Utilizing ultrafast terahertz (THz) magnons, the quanta of collective magnetic excitations, as carriers may provide a promising alternative to overcome the problems associated with electrical losses in nanoelectronic devices and circuits. However, efficient excitation of propagating coherent THz magnons in magnonic nanowaveguides is an essential requirement for the development of such devices. Here, by growing ultrathin ferromagnetic nanostructures on a reconstructed surface, we create well-ordered periodic magnetic nanostripes. We demonstrate that such atomically architectured nanowaveguides not only provide a versatile platform for an efficient generation of THz magnons but also allow for their fast propagation. Our results reveal the complex nature of the spin dynamics within such designed nanowaveguides and pave the way for designing ultrafast magnon-based logic devices with THz operation frequencies.

Based on ab initio calculations, we demonstrate that a Mott insulator LaTiO3 (LTO), not inspected previously as an altermagnetic material, shows the characteristic features of altermagnets, i.e., (i) fully compensated antiferromagnetism and (ii) k-dependent spin-split electron bands in the absence of spin-orbit coupling. The altermagnetic ground state of LTO is protected by the crystal symmetry and specifically ordered d orbitals of Ti ions with the orbital momentum l = 2. The altermagnetism occurs when sites of Ti pairs in the unit cell are occupied by single electrons with m = -1, sz = +1/2 and m = +1, sz = -1/2 per site, with m and sz- being the z-component of the orbital momentum and spin, respectively. By further simulating orbital disorder within the Green's function method, we disclose its damaging character on the spin splitting and the resulting altermagnetism. When the single-electron spin-polarized state at each Ti site is contributed almost equally by two or three t2g orbitals, LTO becomes antiferromagnetic. The effect of the spin-orbit coupling, which can cause orbital disorder and suppress altermagnetism, is discussed.

Intrinsic magnetic topological insulators, in which magnetism and topology are inherently combined, are excellent systems to realize exotic phenomena such as the quantum anomalous Hall effect. However, there are many reports that show that the experimental samples are not so ideal and the effect of the unintentional disorder in these systems needs to be considered carefully. In this study, we investigate the role of misplaced magnetic atoms as well as nonmagnetic elements in the intrinsic magnetic topological insulator heterostructures based on MnBi2Se4 and Bi2Se3. We find that Mn atoms are not only placed at the central layer of the MnBi2Se4 septuple layer (SL) but also intermix with Bi (antisite Mn) as well as reside in the van der Waals (vdW) gap. Through a detailed comparison between the experimental and theoretical x-ray magnetic circular dichroism (XMCD) spectra, we find that the antisite Mn is coupled ferromagnetically, whereas the vdW Mn couple antiferromagnetically to the Mn in the central atomic plane of the SL. Furthermore, we detect a clear XMCD signal in nonmagnetic Se, providing unambiguous evidence of its magnetic interaction with Mn.