Intrinsic Ferromagnetism Research Articles

Although many metal-organic frameworks (MOFs) display magnetic properties, it remains unclear whether intrinsic weak ferromagnetism (WFM) can occur at room temperature within these materials. Here the discovery of the WFM is reported at room temperature in an iron-based zeolitic imidazolate framework (ZIF) glass, specifically Fe(Im)2, where Im is imidazolate. It is found that antiferromagnetic behavior in the crystalline Fe-ZIF transforms into WFM upon melt-quenching, i.e., during the transition to a structurally disordered glassy state. This magnetic transition is attributed to the enhanced exchange interactions between adjacent FeII nodes, resulting from a reduction in the FeII-FeII correlation length from 6.2 Å in the crystalline phase to 6.0 Å in the glass. 57Fe Mössbauer spectroscopy reveals that the order-to-disorder transition leads to a transition of the low-spin-state in FeII to the uniform high-spin state. The modification of the coordination environment induces room-temperature WFM. The finding opens a pathway for the application of MOF glasses in magnetic and spintronic technologies.

The quantum anomalous Hall (QAH) effect, which enables quantized Hall resistance without an external magnetic field, has attracted significant attention in two-dimensional materials for potential applications in low-power electronic devices. In this work, utilizing first-principles calculations, we find that the O-functionalized TiVC MXene (TiVCO2) monolayer, which is previously proposed as an energy material, will be a promising QAH system. The TiVCO2 monolayer possesses robust structural stability from dynamic, thermal, and mechanical perspectives and exhibits intrinsic ferromagnetism with a high Curie temperature of 370 K. Without the spin–orbit coupling (SOC), the TiVCO2 monolayer is a half-metal with quadratic non-Dirac dispersions around the Fermi level. After incorporating SOC, a sizable bandgap opens at the Γ point, but the nontrivial gap is positioned below the Fermi level owing to the valley polarization at the corners of the Brillouin zone. Through electric field modulation or strain engineering, the Fermi level can be adjusted into the SOC gap, giving rise to a QAH insulating state in the TiVCO2 monolayer. The nontrivial topology of the TiVCO2 monolayer is characterized by a quantized Hall conductance and a single gapless edge state in the bulk gap, confirming a non-zero Chern number of C=1. By the hybrid functional calculation, the strained system is revealed to have a sufficient SOC bandgap for the room-temperature QAH effect. Our study demonstrates that the double-metal MXenes can serve as experimentally accessible materials for achieving the intriguing QAH state.

Abstract The search for zero‐gap spin‐polarized materials such as spin‐gapless semiconductors (SGSs) and their interplay with topological phases is of central importance for realizing dissipationless spintronic functionalities, with the quantum anomalous Hall (QAH) effect being a particularly appealing target. Kagome lattices provide a natural platform for such physics owing to their possible Weyl‐like dispersions and strong correlation effects. Here, by first‐principle calculations, the kagome‐lattice Zn2N3 monolayer is identified as a 2D linear SGS that hosts intrinsic ferromagnetism with a Curie temperature of 204 K. In the absence of spin–orbit coupling (SOC), the system exhibits spin‐down Weyl‐like crossings and spin‐up gap at the Fermi level with complete spin polarization. SOC lifts these degeneracies, opening a topological gap and inducing an intrinsic QAH state with Chern number 𝐶 = 1 and chiral edge states, which remain stable under biaxial strain up to 10%. These results establish Zn2N3 as a robust platform for next‐generation spintronic and topological quantum devices with ultralow energy dissipation.

Traditional carbon allotropes, such as graphene, diamond, nanotubes, and fullerenes, are typically nonmagnetic. However, recent experimental observations of intrinsic magnetism challenge conventional theories. The microscopic origin, exchange interactions, and design strategies for magnetic carbon structures, particularly three-dimensional (3D) allotropes, remain elusive. Here, combining first-principles calculations with hybrid orbital analysis, we establish a unified framework showing that magnetism arises from symmetry breaking of unhybridized 2p orbitals within atomic groups exhibiting bent sp-sp2 or trigonal pyramidal sp2-sp3 hybridizations. Distinct from conventional atomic-centered magnetism theories, our atomic-group-based paradigm systematically predicts magnetic carbon allotropes from zero-dimensional to 3D systems. We further propose a general design strategy and predict a family of metastable two-dimensional and 3D phases displaying intrinsic itinerant ferromagnetism or antiferromagnetism. These findings lay the groundwork for a p-block magnetism theory and open avenues for spintronic and quantum material design.

Two-dimensional ferromagnetic semiconductors have attracted great attention due to their applications in the next generation of nanoscale spintronics. However, experimentally confirmed two-dimensional ferromagnetic semiconductors are rather limited and suffer from a rather low Curie temperature. Based on density functional theory, the structure, electronic, and magnetic properties of the CrCl3-xBrx (x = 0, 1, 2, 3) monolayers are systematically explored. As a result, they are all semiconductors with intrinsic ferromagnetism, and their band gaps decrease with increasing Br composition. Interestingly, due to the joint effects of spin-orbit coupling and magnetic dipole-dipole interaction, the magnetic easy axes have a transition from in-plane to out-of-plane with Br composition increasing. In addition, by the isovalent alloying method, the FM coupling of CrCl3-xBrx can be remarkably enhanced, and their Curie temperature can be increased to 120 K, 130 K, 145 K and 170 K without introducing any carriers, respectively. Besides, the CrCl3-xBrx monolayers have good thermal and dynamical stability, and their small exfoliation energies confirm that they can be exfoliated from the bulk flexibly. Our findings not only provide an effective method to improve ferromagnetism in 2D semiconductors but also provide a class of potential candidates for realistic spintronic applications.

Intrinsic ferromagnetism, with coexisting ferroelectric and ferrovalley polarizations in a single two-dimensional semiconductor, is highly desirable for developing next-generation multifunctional nanospintronic devices. Based on first-principles calculations and Monte Carlo simulations, the two-dimensional V2N2O monolayer is predicted to be an indirect bandgap ferromagnetic semiconductor, characterized by a near-room-temperature Curie temperature and an out-of-plane easily magnetized axis. Interestingly, the spontaneous valley polarization can be effectively modulated by the ferroelectric polarization. Remarkably, the anomalous valley Hall effect in the V2N2O monolayer can be controlled by reversing the magnetization. Thus, the V2N2O monolayer is considered a potential candidate for polymorphic memory and multifunctional valley electronic devices.

Spin-gapless semiconductors (SGSs) represent an intriguing class of quantum materials that bridge the gap between half-metallic ferromagnets and conventional semiconductors, offering promising avenues for spintronic applications. The discovery of intrinsic ferromagnetism in ultrathin two-dimensional van der Waals crystals has further fueled interest in exploring magnetism at the ultimate two-dimensional limit. Here, we demonstrate the growth of environmentally stable, atomically thin Co3Sn2S2 nanosheets via a simple hydrothermal method. These nanosheets exhibit robust ferromagnetism with a Curie temperature of ∼100 K and remarkably, host a spin-gapless semiconducting (SGS) state, distinct from the well-known half-metallic Weyl ferromagnetism observed in the bulk counterpart. Structural analysis reveals that enhanced lattice distortion and strain effects in the nanosheets, induced by reduced dimensionality and surface defects, play a critical role in stabilizing this phase. Williamson-Hall analysis confirms the presence of strain, while DFT calculations reveal that strain-induced lattice distortions annihilate the Weyl points and the emergence of SGS semiconductivity. Charge transport measurements indicate a Mott variable-range hopping mechanism, while temperature-dependent conductivity suggests a coexistence of semiconducting and weakly gapless features. These findings not only establish atomically thin Co3Sn2S2 nanosheets as a novel platform for SGS physics but also open up exciting possibilities for strain-engineered topological phases and next-generation spintronic and quantum technologies.

Abstract Herein, we report detailed magnetic characteristics of 10-nm thick Q-carbon films grown over a large area. Following the Bloch spin wave theory, we show that Q-carbon exhibits robust room-temperature ferromagnetism with a surprisingly high Curie temperature of ~ 556 K. The square-root dependence of coercivity on temperature indicates homogeneous magnetic interactions in the sample. Finally, through ferromagnetic resonance spectroscopy measurements, we show that the spin interactions in Q-carbon are strong and intrinsic to the system. We envisage that the intrinsic ferromagnetism in Q-carbon opens a new frontier for carbon-based systems in spintronic devices. Graphical abstract

The coexistence and tunability of ferroic orders in two-dimensional materials hold great promise for next-generation spintronic and memory devices. Here, based on first-principles calculations, we demonstrate that the interplay of chemical substitution and strain engineering enables controlled phase transitions among ferromagnetic, antiferromagnetic, half-metallic, and ferroelectric states in a two-dimensional bimetallic oxyhalide monolayer NbMnO2Cl4. The pristine NbMnO2Cl4 monolayer exhibits intrinsic half-metallic ferromagnetism, with a Curie temperature of 285 K and magnetic anisotropy energy of 225 μeV per Mn atom. The compressive biaxial strain triggers a sequential transition from half-metallic ferromagnetism to ferroelectric–ferromagnetic and subsequently to ferroelectric–antiferromagnetic states. Conversely, tensile biaxial strain drives a direct transition from half-metallic ferromagnetism to a ferroelectric–antiferromagnetic phase. Spin–lattice coupling plays a crucial role in these phase transitions. Moreover, the Curie temperature increases to 540 K at a tensile strain of 6%, and the magnetic anisotropy energy reaches 670 μeV per Mn atom at a compressive strain of −8%. These findings offer an approach for tailoring multiple ferroic orders in two-dimensional materials through the synergistic effects of chemical doping and mechanical strain.

The discovery of two-dimensional (2D) ferromagnetic semiconductors holds significant promise for advancing Moore's law and spintronics in-memory computing, sparking tremendous interest. However, the Curie temperature of explored 2D ferromagnetic semiconductors is much lower than room temperature. Although plenty of 2D room-temperature ferromagnetic semiconductors have been theoretically predicted, there have been formidable challenges in preparing such metastable materials with ordered structures and high stability. Here, utilizing a novel template-assisted chemical vapor deposition strategy, we synthesized layered MnS2 microstructures within a ReS2 template. The high-resolution atomic structure representation revealed that monolayer MnS2 microstructures well crystallize into a distorted T-phase. Room-temperature ferromagnetism was confirmed through vibrating sample magnetometer measurements, microzone magnetism imaging techniques, and transport characterization. Theoretical calculations indicated that the room-temperature ferromagnetism originates from the Mn-Mn short-range interaction. Our observation not only offered the experimental confirmation of the intrinsic room-temperature ferromagnetism in layered MnS2, but also provided an innovative strategy for the growth of 2D metastable functional materials.

Magnetic 2D materials offer a compelling platform for next-generation electrocatalysis by enabling spin-dependent reaction pathways. Among them, layered ferromagnets such as Fe3GeTe2 (FGT) have garnered attention for combining intrinsic ferromagnetism with high predicted oxygen evolution activity. However, the stability of non-oxide ferromagnets in electrochemical environments remains an unresolved challenge, limiting their envisioned applications. In this study, we introduce a structural homolog approach to investigate the origin of FGT's catalytic behavior and the mechanisms underlying its degradation. By comparing FGT with its isostructural analog Fe3GaTe2 (FGaT), we demonstrate that the electrochemical activity of FGT arises primarily from Fe orbitals and is largely insensitive to changes in sublayer composition. Although both materials exhibit similar basal-plane hydrogen evolution performance, FGaT demonstrates significantly lower long-term stability. Density functional theory calculations reveal that this instability arises from weaker Te bonding introduced by Ga substitution. These findings establish structural homologs as a powerful strategy for decoupling catalytic activity from electrochemical deterioration and for guiding the rational design of stable magnetic electrocatalysts.

The 2H-phase of monolayer vanadium diselenide (VSe[Formula: see text]) has recently emerged as a very intriguing material in spintronics due to its intrinsic ferromagnetism with semiconducting properties. In the present work, first-principles based calculations have been employed to systematically study the electronic, magnetic, and optical behaviour of 2D VSe[Formula: see text] for investigating the impact of different external excitations such as strain, electric field, and pressure on the material. Specifically, the magnetic moment, band gap, Curie temperature (T[Formula: see text]), and absorption coefficient could be modulated, as the states near the Fermi level are mainly contributed by the in-plane atomic orbitals. The presence of different electronic phases in 2D VSe[Formula: see text] can be modulated from semiconductor to half-metal and even normal metal under the influence of external stimuli. Furthermore, the in-plane biaxial strain can effectively tune the T[Formula: see text] and attains a maximum value of 354K at [Formula: see text] = 6%. The maximum observed absorption coefficient is found to be 5.05 × 10[Formula: see text] cm[Formula: see text] (at 1.4 eV) under the applied pressure of 30 GPa, indicating that the VSe[Formula: see text] exhibits strong light absorption in the visible region. The unique combination of electronic phases, robust ferromagnetism, and optical activity makes the 2H-VSe[Formula: see text] a suitable candidate for flexible electronic, optoelectronic, and spintronic applications.

Abstract Electrides, characterized by spatially confined anionic electrons, have emerged as a promising class of materials for catalysis, magnetism, and superconductivity. However, transition-metal-based electrides with diverse electron dimensionalities remain largely unexplored. Here, we perform a comprehensive first-principles investigation of Y-Co electrides, focusing on Y3Co, Y3Co2, and YCo. Our calculations reveal a striking dimensional evolution of anionic electrons: from two-dimensional (2D) confinement in YCo, to one-dimensional (1D) in Y3Co2, and zero-dimensional (0D) in Y3Co. Remarkably, the YCo monolayer exhibits intrinsic ferromagnetism with a magnetic moment of 0.65 μB per formula unit, driven by spin-polarized anionic electrons mediating long-range coupling between Y and Co ions. The monolayer also shows a low exfoliation energy (1.66 J/m2), suggesting experimental feasibility. All three electrides feature low work functions (2.76-3.11 eV) and Co-centered anionic states. This work expands the family of transition-metal-based electrides and highlights dimensionality engineering as a powerful strategy for tuning electronic and magnetic properties.

Abstract The emerging class of two-dimensional piezoelectric ferromagnetic (PFM) systems, combining intrinsic ferromagnetism and piezoelectricity, has attracted significant attention for their potential in multifunctional spintronic devices. In this work, we systematically investigate the electronic structure, magnetic properties, and piezoelectric performance of Janus MoTeX (X = Cl, Br, I) monolayers using first-principles calculations and Monte Carlo simulations. Our results demonstrate that these MoTeX monolayers are stable intrinsic ferromagnetic semiconductors. The Janus-structured MoTeCl, MoTeBr, and MoTeI monolayers exhibit out-of-plane piezoelectric coefficients (d 31) of 1.42, 1.08, and 0.50 pm V−1, respectively, surpassing most reported 2D materials. This enhanced piezoelectricity originates from the broken inversion symmetry along the vertical direction. Notably, MoTeCl, MoTeBr, and MoTeI monolayers display high Curie temperatures (T c ), with values of 190, 219, and 249 K. Furthermore, Janus MoTeX monolayers exhibit excellent mechanical flexibility. The application of biaxial tensile strain engineering significantly improves the PFM performance of MoTeCl monolayers: a 2% strain elevates T c to room temperature and induces a transition of the easy magnetization axis from in-plane to out-of-plane, substantially enhancing their practical applicability. These findings highlight Janus MoTeX monolayers as promising candidates for developing next-generation multifunctional spintronic devices.

Unraveling the microscopic origin of out of plane magnetic anisotropy in VI3

Magnetic transition in nonmetals requires the presence of a considerable proportion of magnetic spins. A new type of ferromagnet named dilute ferromagnetism that contradicts this well‐established concept is proposed for semiconductors of ZnO etc. but has remained experimentally unproven. In this study, an unconventional superlong‐range magnetic coupling and ferromagnetic spin freezing are reported, which can be viewed as an experimental realization of an intrinsic dilute ferromagnetism, in mechanoluminescent material of EuxSr1‐xAl2O4 (x = 0.2−2%), wherein Eu is sparsely incorporated into the lattice to substitute Sr. Ferromagnetic coupling appears below ≈80 K and fully saturated ferromagnetic magnetization appears below ≈3 K, with an unusually large magnetic moment of ≈14 µB per Eu2+. Muon spin spectroscopy demonstrates intrinsic spin freezing with a spontaneous internal field developed below TC of ≈3 K. The neighboring magnetic Eu2+ ions in the lattice have an exceptionally large separation more than one order of magnitude larger than those in conventional magnets, marking it as a unconventional magnetic order over a superlong distance. Bound magnetic polarons arising from electrons trapped at oxygen vacancies may account for this unconventional ferromagnetism. Magnetization under light radiation supports this scenario.

Abstract The coexistence of intrinsic ferromagnetism and high Curie temperature is critical for advanced multifunctional spintronic technologies. Two-dimensional (2D) ferromagnetic (FM) materials, which enable simultaneous control of charge and spin degrees of freedom, represent a promising solution to this challenge. Using first-principles calculations and Monte Carlo simulations, we investigate strain-regulated magnetic properties—specifically magnetic anisotropy energy (MAE) and Curie temperature (TC) of MnAsBr and MnAsI monolayers (MLs). Our calculations reveal out-of-plane magnetic anisotropy energies (MAE) of 0.90 meV and 2.87 meV per unit cell for MnAsBr and MnAsI MLs, respectively, with corresponding Curie temperatures of 439 K and 522 K. Under 5% tensile strain, the MAE increases to 1.58 meV (MnAsBr) and 3.14 meV (MnAsI), while TC rises to 505 K and 544 K for the respective ML systems. These findings demonstrate that MnAsBr and MnAsI monolayers are compelling candidates for flexible spintronic devices.

Spin Hall nano-oscillators (SHNOs) are emerging spintronic oscillators with significant potential for technological applications, including microwave signal generation, and unconventional computing. Despite their promising applications, SHNOs face various challenges, such as high energy consumption and difficulties in growing high-quality thin film heterostructures with clean interfaces. Here, single-layer topological magnetic Weyl semimetals open a possible solution as they possess both intrinsic ferromagnetism and a large spin-orbit coupling due to their topological properties. However, producing such high-quality thin films of magnetic Weyl semimetals that retain their topological properties and Berry curvature remains a challenge. We address these issues with high-quality single-layer epitaxial ferromagnetic Co2MnGa Weyl semimetal thin film-based SHNOs. We observe a giant spin Hall conductivity, σSHC = (6.08 ± 0.02) × 105 (ℏ/2e) Ω-1 m-1, which is an order of magnitude higher than previous reports. Theoretical calculations corroborate the experimental results with a large intrinsic spin Hall conductivity due to presence of a strong Berry curvature. Further, self spin-orbit torque driven magnetization auto-oscillations are demonstrated for the first time, at an ultralow threshold current density of Jth = 6.2 × 1011 A m-2. These findings indicate that magnetic Weyl semimetals have tremendous application potential for developing energy-efficient spintronic devices.

Ferrovalley materials are valleytronic materials with intrinsic ferromagnetism, in which the presence of spontaneous valley polarization is more conducive to practical applications. The optical properties of ferrovalley are important for selectively exciting electrons at the valley. In this paper, the electronic and optical spectrum of the H-phase FeCl2monolayer is studied using first-principles calculations as an example. We use hybrid functional HSE06 and GW0 methods with spin-orbit coupling for our calculations, the band gap of H-FeCl2is about 3.975 and 4.072 eV at K and -K valley, which is significantly larger than that obtained by the PBE method, with a 97 meV valley splitting. It is shown that the monolayer H-FeCl2is a ferrovalley material with an ultra-wide band gap and large intrinsic valley polarization, which has strong electronic correlation and many-body effects. Calculation of the imaginary part of the dielectric function using GW-BSE method shows that the energy corresponding to the exciton peak is 2.421 and 2.491 eV, much smaller than the GW band gap. The exciton binding energy is about 1.554 and 1.581 eV at K and -K valley, indicating a large exciton effect. And the exciton binding energy of the two valleys are unequal, with a difference of 27 meV. It is found that splitting occurs at the first exciton peak in the ferrovalley material, and the splitting value is inequivalent to the bandgap splitting at the valley, which is instructive for further research as well as application of the valleytronics.

The investigation of two-dimensional (2D) intrinsic ferromagnetic material is important in the field of spintronics. In this study, the Mn2Ge2Te6 monolayer (ML) with intrinsic ferromagnetism was fabricated by using the density functional theory (DFT). The Mn2Ge2Te6 ML is a half metal (HM) with a spin-β bandgap of 1.462 eV. Biaxial strain could be applied to tune the electronic and magnetic properties of Mn2Ge2Te6. The magnetic moment (MM), magnetic exchange parameter (J), band structures, and magnetic anisotropy energy (MAE) could be effectively controlled by the biaxial strains (ε). This modulation originates that the states near the Fermi level mainly come from the contribution of in-plane atomic orbitals. The MM of Mn monotonously increases as the tensile strains increase. The energy difference between different magnetic orders (ΔE) and J also change with the strains. The antiferromagnetic-stripy order always has the lowest energy under the strains. As the strains change, ΔE and J monotonously change as the direct exchange and super-exchange interactions between Mn atoms vary. As the tensile strain decreases and compressive strain increases (−2.1%<ε<8%), the gap of spin-β electrons monotonously decreases. The Mn2Ge2Te6 ML changes from a HM to a normal spin-unpolarized metal under larger compressive strains (ε>−2.1%). When the tensile strains are applied, the MAE monotonously increases to the largest value of −22.3 meV (ε=12%). As the compressive strains increase, the MAE monotonously decreases. Last, the Mn2Ge2Te6 ML changes from an in-plane magnetic anisotropy into a perpendicular magnetic anisotropy under a larger compressive strain (−11%). The change of MAE direction origins that the contribution of hybridization between Te's py and pz orbitals is changed when the strain changes. Our results offer crucial insights into the potential of strain modulation in a 2D Mn2Ge2Te6 ML, paving the way for future advancements in this field.