Exploring altermagnetism in RuO2: from conflicting experiments to emerging consensus.

The magnetic microstructure of rolled-up magnetic nanomembranes is revealed both theoretically and experimentally. Two types of nanomembranes are considered, one with a non-magnetic spacer layer and the other without. Experimentally, by using different materials and tuning the dimensions of the rolled-up nanomembranes, domain patterns consisting of spiral-like and azimuthally magnetized domains are observed, which are in qualitative agreement with the theoretical predictions.

Available reports mentioned that the magnetic ground state in the AA-stacked bilayer zigzag graphene nanoribbons is the non-magnetic state. As a consequence, it is impossible to exploit magnetism for future electronic devices. This paper aims to show how to generate magnetism in the AA-stacked bilayer zigzag graphene nanoribbons by employing ?rst-principles calculations. As we stacked different ribbon widths, the magnetic ground states appeared for all the thicknesses. In general, the G-type antiferromagnetic state, which is the antiferromagnetic alignment between both intraplane- and interplane-edge carbon atoms, is the ground state for all the thicknesses. We also found that the degenerate magnetic ground states and excited states may appear under certain thicknesses, thus yielding the richness of the magnetic state. As hole-electron doping was applied, a phase transition of magnetic ground state emerged for certain thicknesses, indicating that a new magnetic ground state in the AA-stacked bilayer zigzag graphene nanoribbons can be tuned by the doping.

We employ the locally self-consistent Green's function technique and exact muffin-tin orbital method to investigate magnetic state and ground state properties of Invar ${\mathrm{Fe}}_{65}{\mathrm{Ni}}_{35}$ alloy. We show that it is in a chemically disordered state, characterized by a relatively small amount of atomic short-range order, above the magnetic ordering temperature. We speculate that it should remain in this state below the Curie temperature upon applying usual heat treatment for the Invar alloys. The magnetic state at the experimental lattice spacing is shown to be sensitive to the type of approximation for the exchange-correlation functional: While the magnetic ground state is purely ferromagnetic in the generalized gradient approximation, there is a small amount of Fe atoms with magnetic moment antiferromagnetically aligned relative to the global magnetization in the local density approximations. The local spin-density approximation, however, fails to yield correctly the equilibrium lattice spacing, whereas the generalized gradient approximation reproduces it reasonably well. The anomalous spontaneous volume magnetostriction leading to the Invar effect is found to be $\ensuremath{\approx}3%$, in fair agreement with the experimental estimate of $\ensuremath{\approx}2.2%$.

By the local density approximation with on-site Coulomb repulsion U (LDA +U) method with spin-orbit coupling (LDA+U+SO) the magnetic state and electronic structure have been investigated for plutonium in δ and α phases and for the Pu compounds PuN, PuCo Ga5, Pu Rh2, Pu Si2, PuTe, and PuSb. In agreement with experiment we found for metallic plutonium in both phases a nonmagnetic ground state with Pu ions in f6 configuration with zero values of spin, orbital, and total moments. This result is determined by a strong spin-orbit coupling in the 5f shell. It leads to the clear splitting of 5f states into f52 and f72 subbands even in the LDA calculation. The Fermi level is in a pseudogap between them, so that the f52 subshell is already almost completely filled with six electrons before Coulomb correlation effects are taken into account. The competition between spin-orbit coupling and the exchange (Hund) interaction (favoring a magnetic ground state) in the 5f shell is so delicately balanced that a small increase (less than 15%) of the exchange interaction parameter value from JH =0.48 eV obtained in the constrained LDA calculation would result in a magnetic ground state with nonzero spin and orbital moment values. For the Pu compounds investigated in the present work, a predominantly f6 configuration with nonzero magnetic moments was found in PuCo Ga5, Pu Si2, and PuTe, while PuN, Pu Rh2, and PuSb have the f5 configuration with sizable magnetic moment values. Whereas the pure jj coupling scheme was found to be valid for metallic plutonium, an intermediate coupling scheme is needed to describe the 5f shell in Pu compounds. The results of our calculations show that the exchange interaction term in the Hamiltonian should be treated in a general matrix form for Pu and its compounds. © 2005 The American Physical Society.

Magnetic properties of multiferroic Eu1-xYxMnO3 with x = 0.2, 0.3 were studied by μSR and Mossbauer spectroscopy. Both compounds are known to become antiferromagnetic with Mn3+ being the only magnetic ion. We find TN = 47±0.5K for x = 0.2 and 45±0.5K for x = 0.3. Below TN three different magnetic states (AFM-1, AFM-2, AFM-3) are formed. The μSR parameters of the uppermost magnetic state (AFM-1) are alike in both compounds, and compatible with a commensurate modulated collinear spin structure. The magnetic ground state in x = 0.2 (AFM-3) is shown to be single phase. Its spectral parameters support the proposal of a cone-like spin structure, yet with incommensurate modulation. The ground state for x = 0.3 is found to have an incommensurate spiral spin structure. 151Eu Mössbauer spectroscopy measured the Eu hyperfine field induced by the Mn3+ ions. Its low value (~4T) means that mixing with higher Eu electronic states is small and that the Mn-Eu exchange coupling is weak (~0.5K). The various magnetic transitions appear as small irregularities in the temperature dependence of the hyperfine fields. The present results are discussed in terms of different published magnetic phase diagrams of Eu1-xYxMnO3.

The magnetic ground state of (Sr$_{1-x}$Ca$_x$)$_3$Ru$_2$O$_7$ (0 $\\leq x\n\\leq$ 1) is complex, ranging from an itinerant metamagnetic state (0 $\\leq x <$\n0.08), to an unusual heavy-mass, nearly ferromagnetic (FM) state (0.08 $< x <$\n0.4), and finally to an antiferromagnetic (AFM) state (0.4 $\\leq x \\leq$ 1). In\nthis report we elucidate the electronic properties for these magnetic states,\nand show that the electronic and magnetic properties are strongly coupled in\nthis system. The electronic ground state evolves from an AFM\nquasi-two-dimensional metal for $x =$ 1.0, to an Anderson localized state for\n$0.4 \\leq x < 1.0$ (the AFM region). When the magnetic state undergoes a\ntransition from the AFM to the nearly FM state, the electronic ground state\nswitches to a weakly localized state induced by magnetic scattering for $0.25\n\\leq x < 0.4$, and then to a magnetic metallic state with the in-plane\nresistivity $\\rho_{ab} \\propto T^\\alpha$ ($\\alpha >$ 2) for $0.08 < x < 0.25$.\nThe system eventually transforms into a Fermi liquid ground state when the\nmagnetic ground state enters the itinerant metamagnetic state for $x < 0.08$.\nWhen $x$ approaches the critical composition ($x \\sim$ 0.08), the Fermi liquid\ntemperature is suppressed to zero Kelvin, and non-Fermi liquid behavior is\nobserved. These results demonstrate the strong interplay between charge and\nspin degrees of freedom in the double layered ruthenates.\n

First principles calculations reveal that the antiferromagnetic double layer (AFMD) along the magnetization direction of 〈0 0 1〉 is the magnetic ground state of face-centered-cubic (FCC) structure of iron (Fe) due to its lowest total energy among all the studied magnetic states. This magnetic ground state of AFMD-〈0 0 1〉 is fundamentally due to a stronger chemical bonding in terms of electronic structure, and could be confirmed by its mechanical properties for the first time. Calculations also show that lattice constant has an important effect to determine the magnetic state of FCC Fe, and a transition of magnetic state between AFMD-〈0 0 1〉 and ferromagnetic happens at the critical lattice constant of 3.666 Å. The derived results are in good agreement with experimental and theoretical observations, and could clarify the controversy regarding magnetic ground state of FCC Fe in the literature.

This paper discusses the prospects for using magnetic nanostructures as elements of neural networks. At present neural network learning programs are actively used in analyzing and processing large data arrays; however, the development of computer technologies based on the neural network principle still remains open. Possibilities for using magnetic elements as physical carriers of information bits in these systems attract much attention from researchers and technologists due to the presence of several easily controlled parameters (order parameter) in the magnetic system, possibilities for the dimensionality reduction in magnetic elements by using magnetic nanostructures (domain boundaries, vortices, ckyrmions), superquick switching between magnetic states and some other factors. One of the key aspects of research in this regard is to determine basic controlled magnetic parameters in restricted geometries and to identify ways of controlling these parameters through internal and external factors. The paper presents a research on the magnetic ground state in restricted geometries. It deals with the magnetic state rebuilding in the system under changes in both external factors (applied magnetic field, sample dimensions) and internal ones (magnetic anisotropy constant, Dzyaloshinskii-Moriya interaction constant). Calculations were performed within the framework of micromagnetic modelling using the Object Oriented MicroMagnetic Framework ( OOMMF) sogtware. It is shown that the anisotropic exchange interaction (Dzyaloshinskii-Moriya interaction) has a significant effect on the magnetization distribution in restricted geometries. Namely, when changing the value of the Dzyaloshinskii-Moriya constant in the system with uniaxial magnetic anisotropy there is a series of phase transitions observed between magnetic states of different types: transitions from the homogenous magnetic state into the skyrmion-type vortex state (domain structure with the skyrmion-type unidomain state) with subsequent domain structure reversal when changing the value of the Dzyaloshinskii-Moriya constant. In the case of magnetic anisotropy of easy -axis type, chirality and properties of the structures in question do not depend on the constant symbol of the Dzyaloshinskii-Moriya interaction.

The success of descriptor-based material design relies on eliminating bad candidates and keeping good candidates for further investigation. While DFT has been widely successfully for the former, often times good candidates are lost due to the uncertainty associated with the DFT-predicted material properties. Uncertainty associated with DFT predictions has gained prominence and has led to the development of exchange correlation functionals that have built-in error estimation capability. In this work, we demonstrate the use of built-in error estimation capabilities within the BEEF-vdW exchange correlation functional for quantifying the uncertainty associated with the magnetic ground state of solids. We demonstrate this approach by calculating the uncertainty estimate for the energy difference between the different magnetic states of solids and compare them against a range of GGA exchange correlation functionals as is done in many first principles calculations of materials. We show that this estimate reasonably bounds the range of values obtained with the different GGA functionals. The estimate is determined as a post-processing step and thus provides a computationally robust and systematic approach to estimating uncertainty associated with predictions of magnetic ground states. We define a confidence value (c-value) that incorporates all calculated magnetic states in order to quantify the concurrence of the prediction at the GGA level and argue that predictions of magnetic ground states from GGA level DFT is incomplete without an accompanying c-value. We demonstrate the utility of this method using a case study of Li and Na-ion cathode materials and the c-value metric correctly identifies that GGA level DFT will have low predictability for NaFePO$_4$F.

Controllable magnetic ground states in metal diiodide MI2 (M: Fe, Co, and Ni) monolayers by electric field

Achieving tunable magnetism in low-dimensions is an essential step to realize novel spintronic applications. In this manner, two-dimensional transition metal carbides/nitrides (MXenes) with intrinsic magnetism have attracted significant interest. In this study, we extensively examine the structural and magnetic properties of 1T- and 2H-Ti2C monolayers by using first-principles techniques. We reveal the dynamical stability of both phases by using phonon spectra analysis and abinitio molecular dynamics simulations. The magnetic ground state is determined by considering all possible spin configurations and taking into account spin–orbit coupling effects, strong onsite Coulomb interaction, and corrected self-interaction terms. Our results indicate that while 1T-Ti2C is anti-ferromagnetic, 2H-Ti2C exhibits ferromagnetism, which is stable at/above room temperature. The electronic structure analysis demonstrates that 1T-Ti2C is an indirect bandgap semiconductor and 2H-Ti2C is a half-metal with 100% spin-polarization. Additionally, it is shown that the magnetic state is robust against low mechanical deformations and fundamental bandgap (also half-metallic bandgap) can be tuned by compressive/tensile strain. Phase-dependent and tunable electronic and magnetic properties of Ti2C monolayers offer new opportunities in the field of low-dimensional magnetism.

Topological chiral antiferromagnets, such as Mn3Sn, are emerging as promising materials for next‐generation spintronic devices due to their intrinsic transport properties linked to exotic magnetic configurations. Here, it is demonstrated that anisotropic strain in Mn3Sn thin films offers a novel approach to manipulate the magnetic ground state, unlocking new functionalities in this material. Anisotropic strain reduces the point group symmetry of the manganese (Mn) Kagome triangles from C3v to C1, significantly altering the energy landscape of the magnetic states in Mn3Sn. This symmetry reduction enables even a tiny in‐plane Dzyaloshinskii‐Moriya (DM) interaction to induce canting of the Mn spins out of the Kagome plane. The modified magnetic ground state introduces a finite scalar spin chirality and results in a significant Berry phase in momentum space. Consequently, a large anomalous Hall effect emerges in the Kagome plane at room temperature ‐ an effect that is absent in the bulk material. Moreover, this twofold degenerate magnetic state enables the creation of multiple‐stable, non‐volatile anomalous Hall resistance (AHR) memory states. These states are field‐stable and can be controlled by thermal‐assisted current‐induced magnetization switching, requiring modest current densities and small bias fields, thereby offering a compelling new functionality in Mn3Sn for spintronic applications.

Emerging topological states in EuMn2Bi2: A first principles prediction

Here, the magnetic behavior of Sn-substituted Sr<sub>2</sub>IrO<sub>4</sub> has been examined through magnetization measurements and single-crystal neutron diffraction on Sr<sub>2</sub>Ir<sub>1-x</sub>Sn<sub>x</sub>O<sub>4</sub> for 0.05≲x≲0.35. For all x examined, the magnetic ground state is similar to that induced in Sr<sub>2</sub>IrO<sub>4</sub> by application of a magnetic field. This magnetic state is characterized by a small net moment due to the alignment of canted moments within an otherwise antiferromagnetic structure. The weak ferromagnetic behavior is observed in the magnetization data for both unique crystallographic orientations. Diffraction data reveal an anisotropic response in the lattice parameters, with an overall lattice expansion, as well as a small reduction in the rotation of the IrO<sub>6</sub> octahedra. Lastly, the magnetic ordering temperature is continually suppressed with increasing x, and long-range magnetic order persists to the highest Sn concentrations synthesized.

Magnetic frustration, the competition among exchange interactions, often leads to novel magnetic ground states with unique physical properties which can hinge on details of interactions that are otherwise difficult to observe. Such states are particularly interesting when it is possible to tune the balance among the interactions to access multiple types of magnetic order. We present antlerite, Cu$_3$SO$_4$(OH)$_4$, as a potential platform for tuning frustration. Contrary to previous reports, the low-temperature magnetic state of its three-leg zigzag ladders is a quasi-one-dimensional analog of the magnetic state recently proposed to exhibit spinon-magnon mixing in botallackite. Density functional theory calculations indicate that antlerite's magnetic ground state is exquisitely sensitive to fine details of the atomic positions, with each chain independently on the cusp of a phase transition, indicating an excellent potential for tunability.