Robust Room Temperature Ferromagnetism Research Articles

Transition metal doping for tailoring magnetic properties of graphdiyne

Tailoring the magnetic properties of semiconductors is crucial for realizing spintronic devices with integrated logic and memory functions. Graphdiyne (GDY), a two-dimensional carbon semiconductor, has emerged as a promising material for this purpose. This work demonstrates an effective approach to induce robust room-temperature ferromagnetism in GDY through in-situ transition metal (Fe, Co, Ni) doping via an improved liquid-liquid interface synthesis method. Density functional theory calculations reveal that the ferromagnetism originates from the Kagome lattice formed by the doped transition metal atoms. Remarkably, Fe-doped GDY exhibits a saturation magnetization of 2.86 emu · g−1 at room temperature, substantially higher than Co- and Ni-doped counterparts. Furthermore, post synthesis annealing treatment allows modulating the magnetic properties by introducing hydroxyl groups, with Co-GDY annealed at 500°C showing optimal room-temperature ferromagnetic behavior (0.26 emu · g−1). This work paves the way for tailoring magnetic semiconductors for spintronic applications by leveraging transition metal doping and defect engineering in graphdiyne.

Air-Stable Wafer-Scale Ferromagnetic Metallo-Carbon Nitride Monolayer.

The pursuit of robust, long-range magnetic ordering in two-dimensional (2D) materials holds immense promise for driving technological advances. However, achieving this goal remains a grand challenge due to enhanced quantum and thermal fluctuations as well as chemical instability in the 2D limit. While magnetic ordering has been realized in atomically thin flakes of transition metal chalcogenides and metal halides, these materials often suffer from air instability. In contrast, 2D carbon-based materials are stable enough, yet the challenge lies in creating a high density of local magnetic moments and controlling their long-range magnetic ordering. Here, we report a novel wafer-scale synthesis of an air-stable metallo-carbon nitride monolayer (MCN, denoted as MN4/CNx), featuring ultradense single magnetic atoms and exhibiting robust room-temperature ferromagnetism. Under low-pressure chemical vapor deposition conditions, thermal dehydrogenation and polymerization of metal phthalocyanine (MPc) on copper foil at elevated temperature generate a substantial number of nitrogen coordination sites for anchoring magnetic single atoms in monolayer MN4/CNx (where M = Fe, Co, and Ni). The incorporation of densely populating MN4 sites into monolayer MCN networks leads to robust ferromagnetism up to room temperature, enabling the observation of anomalous Hall effects with excellent chemical stability. Detailed electronic structure calculations indicate that the presence of high-density metal sites results in the emergence of spin-split d-bands near the Fermi level, causing a favorable long-range ferromagnetic exchange coupling through direct exchange interactions. Our work demonstrates a novel synthesis approach for wafer-scale MCN monolayers with robust room-temperature ferromagnetism and may shed light on practical electronic and spintronic applications.

Realizing Room-Temperature Ferromagnetism in Molecular-Intercalated Antiferromagnet VOCl.

2D van der Waals (vdW) magnets are gaining attention in fundamental physics and advanced spintronics, due to their unique dimension-dependent magnetism and potential for ultra-compact integration. However, achieving intrinsic ferromagnetism with high Curie temperature (TC) remains a technical challenge, including preparation and stability issues. Herein, an applicable electrochemical intercalation strategy to decouple interlayer interaction and guide charge doping in antiferromagnet VOCl, thereby inducing robust room-temperature ferromagnetism, is developed. The expanded vdW gap isolates the neighboring layers and shrinks the distance between the V-V bond, favoring the generation of ferromagnetic (FM) coupling with perpendicular magnetic anisotropy. Element-specific X-ray magnetic circular dichroism (XMCD) directly proves the source of the ferromagnetism. Detailed experimental results and density functional theory (DFT) calculations indicate that the charge doping enhances the FM interaction by promoting the orbital hybridization between t2 g and eg. This work sheds new light on a promising way to achieve room-temperature ferromagnetism in antiferromagnets, thus addressing the critical materials demand for designing spintronic devices.

Growth of 2D Cr2 O3 -CrN Mosaic Heterostructures with Tunable Room-Temperature Ferromagnetism.

2D magnets have generated much attention due to their potential for spintronic devices. Heterostructures of 2D magnets are interesting platforms for exploring physical phenomena and applications. However, the controlled growth of 2D room-temperature ferromagnetic heterostructures is challenging. Here, one-pot chemical vapor deposition growth of stable 2D Cr2 O3 -CrN mosaic heterostructures (MHs) is reported with a controlled ratio of components that possess robust room-temperature ferromagnetism. The 2D MHs consist of Cr2 O3 flakes with embedded CrN subdomains and the CrN:Cr2 O3 ratio can be tuned from 0% to 100% during growth. By changing the CrN:Cr2 O3 ratio, the ferromagnetism of the MHs (e.g., saturation magnetization, coercive field), which originates from the interfacial coupling between Cr2 O3 and CrN, can be controlled. Importantly, the obtained Cr2 O3 -CrN MHs are stable in air at elevated temperatures and have robust ferromagnetism with Curie temperature >400K. This work presents a facile method for fabricating 2D MHs with tunable magnetism which will benefit high-temperature spintronics.

Tuning the magnetic properties of doped ZnS using transition metal doping: A multi-scale computational approach

Transition metal (TM)-doped dilute magnetic semiconductors (DMS) have emerged as promising materials for spintronic applications such as spin-polarized transport and information storage. However, achieving robust room-temperature ferromagnetism in DMS remains a key challenge. This work undertakes a comprehensive investigation of the effects of Ti- and Cr-doping and (Ti,Cr)-codoping on the structural, electronic, and magnetic properties of wurtzite ZnS using first-principles pseudopotential plane-wave self-consistent field calculations and Monte Carlo simulations. The first-principles DFT calculations were performed using the spin-polarized GGA+U approach to account for strong electron–electron interactions. Structural relaxations revealed expanded lattice parameters and bond lengths for the doped systems compared to pure ZnS, attributed to the larger ionic radii of the dopants. Formation energy calculations confirmed the thermodynamic stability of doping. The band structure and density of states analysis demonstrated the half-metallic nature of the doped ZnS systems with 100% spin polarization induced by strong hybridization between the TM-3d and S-3p states. This mediates robust ferromagnetic coupling, with total magnetic moments around 4-8 μB/cell depending on dopant type and concentration. To complement the zero-temperature DFT results, temperature-dependent Monte Carlo simulations using the single-spin flip Heat Bath algorithm were implemented. The modeling of magnetization, susceptibility, specific heat, and hysteresis loops enabled extracting Curie temperatures up to 427.6 K for 12.5% Cr-doped ZnS. The synergistic combination of first-principles DFT and Monte Carlo computational techniques provides significant insights into tailoring the magnetic properties of TM-doped ZnS dilute magnetic semiconductors. The tunability of structural, electronic, and magnetic characteristics through control of dopant selection and concentration demonstrates the promising potential of transition metal-doped ZnS for spintronic devices operable at room-temperature.

Non-stoichiometry induced 2H–1T phase interfaces and room-temperature ferromagnetism in defective molybdenum selenide

Magnetic semiconducting materials offer tremendous prospects for spin electronics but is challenging to achieve room-temperature ferromagnetism with unambiguous origin. Herein, a non-stoichiometry strategy is proposed to induce tunable magnetization in MoSe2−x nanoflowers via vacancy-controlled 2H–1T phase transition. The resultant MoSe2−x exhibits robust room-temperature ferromagnetism with significant positive correlation to the content of 1T phase and 2H–1T interfaces. Significant magnetic hysteresis and Curie transition above room temperature have been achieved, confirming the ferromagnetic feature of MoSe2−x. To examine the origin of ferromagnetism, formation energy and spin-polarized calculations have been conducted, indicating that the Se vacancy is beneficial for the formation of the 1T phase and interfacial spin polarization. Localized magnetic moments induced at the 2H–1T interfaces exhibit enhanced magnetism as compared to the net moments from the 1T orbital splitting, giving rise to strong coupling bound magnetic polarons. This work not only advances the understanding on the origin of magnetism in magnetic semiconductors, but also provides an effective route to generate ferromagnetism by defect and/or interface engineering that could be applied to multiferroics, spintronics, and valleytronics.

Stacking order, charge doping, and strain-induced switching between AFM and FM in bilayer GdI2

GdI2 monolayer is a promising material for spintronics applications due to its robust room-temperature ferromagnetism and sizable valley polarization. In two-dimensional van der Waals magnets, interlayer magnetic coupling plays a crucial role in device applications. The performance of these devices can be effectively tuned by adjusting the stacking order, charge doping, and strain. By performing first-principles calculations, we have demonstrated that the interlayer magnetic coupling in bilayer GdI2 is highly dependent on the stacking order, which can be tuned between ferromagnetic (FM) and antiferromagnetic orders through lateral shifting. Furthermore, the interlayer magnetic coupling can also be tuned by charge doping and strain, where both electron and hole doping can enhance the FM coupling interaction between layers, and the interlayer FM coupling can be strengthened with increasing biaxial tensile strain. These results show that bilayer GdI2 has rich tunable interlayer magnetic interactions, which can be used in designing interesting spin tunnel field-effect transistor devices.

Supercritical CO2 -induced New Chemical Bond of C-O-Si in Graphdiyne to Achieve Robust Room-Temperature Ferromagnetism.

The realization of ferromagnetic ordering of two-dimensional (2D) carbon material graphdiyne (GDY) has attracted great attention due to its promising application in spin semiconductor devices. However, the absence of localized spins makes the pristine GDY intrinsically nonferromagnetic. Herein, we report the realization of robust room-temperature (RT) ferromagnetism (FM) with Curie temperature (TC ) up to 325 K for GDY Nanosheets (GDYNs) by supercritical CO2 (SC CO2 ). Experimental and theoretical calculations reveal that the new chemical bond of C-O-Si can be formed because of the unique effect of SC CO2 , which help to enhance the charge transfer and generates long-range ferromagnetic order. The RT saturation magnetization (MS ) reaches 1.125 emu/g, which is much higher than that of carbon-based materials reported up to now. Meanwhile, by changing the conditions of SC CO2 such as pressure, ferromagnetic responses can be manipulated, which is great for potential spintronics applications of GDY.

Ultrathin high-temperature ferromagnetic rare-earth films: GdScGe and GdScSi monolayers

Two-dimensional (2D) ferromagnetism with robust room-temperature ferromagnetism has sparked intense interest for future miniature information storage devices. However, most 2D ferromagnetic materials have a low Curie temperature. Here, by using density functional theory, two rare-earth monolayers, the GdScSi monolayer and the GdScGe monolayer, were predicted, in which these two monolayers exhibit ferromagnetic orders with large magnetic moments of approximately 7 μB/Gd. Monte Carlo simulations predict Curie temperatures of approximately 470 K and 495 K for the 2D GdScSi monolayer and the GdScGe monolayer, respectively. The spin band calculations show that they are metal. In addition, these two monolayers exhibit dynamical, mechanical, and thermal stabilities. The combination of these novel magnetic properties makes these 2D ferromagnetic crystals promising candidates for high-efficiency spintronic applications.

Large-scale fabrication and Mo vacancy-induced robust room-temperature ferromagnetism of MoSe2 thin films.

Molybdenum selenide (MoSe2) has recently attracted particular attention due to its room-temperature ferromagnetism (RTFM) and related spintronic applications. However, not only does the FM mechanism of MoSe2 remain controversial, but also the synthesis of MoSe2 thin films with robust RTFM is still an unmet challenge. Here it is shown that using polymer-assisted deposition under appropriate growth conditions, large-scale (4 cm × 4 cm) synthesis of MoSe2 thin films with robust RTFM and a smooth surface (roughness average ∼0.22 nm) is possible. A new record-high saturation magnetization (6.69 emu g-1) is achieved in the prepared MoSe2 thin films, about 5 times the previously reported record (1.39 emu g-1) obtained in 2H-MoSe2 nanoflakes. Meanwhile, the coercivity of the MoSe2 films can be tuned down to a new record-low value (5.0 Oe), one-tenth of the previously reported record. Notably, detailed analysis combining the experimental findings and calculation results shows that the robust RTFM mainly comes from the Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction between the magnetic moments induced by abundant Mo vacancies (VMos) in the MoSe2 films. Our results give insights into the large-scale production and robust RTFM of MoSe2 thin films and may provide a platform for designing and fabricating spintronic materials and devices based on transition-metal dichalcogenides.

Robust Room Temperature Ferromagnetism In Cobalt Doped Graphene by Precision Control of Metal Ion Hybridization

AbstractGraphene‐based magnetic materials exhibit novel properties and promising applications in the development of next‐generation spintronic devices. Modern synthesis techniques have paved the way to design precisely the local environments of metal atoms anchored onto a nitrogen‐doped graphene matrix. Herein, it is demonstrated that grafting cobalt (Co) into the graphene lattice induces robust and stable room‐temperature ferromagnetism. These comprehensive experiments and first‐principles calculations unambiguously identify that the mechanism for this unusual ferromagnetism is π‐d orbital hybridization between Co dxz and graphene pz orbitals. Here, it is found that the magnetic interactions of Co–carbon ions are mediated by the spin‐polarized graphene pz orbitals, and room temperature ferromagnetism can be stabilized by electron doping. It is also found that the electronic structure near the Fermi level, which sets the nature of spin polarization of graphene pz bands, strongly depends on the local environment of the Co moiety. This is the crucial, previously missing, ingredient that enables control of the magnetism. Overall, these observations unambiguously reveal that engineering the atomic structure of metal‐embedded graphene lattices through careful d to p orbital interactions opens a new window of opportunities for developing graphene‐based spintronics devices.

Robust room-temperature ferromagnetism induced by defect engineering in monolayer MoS2

Magnetism in two-dimensional materials is of great importance for exploring new physical phenomena and developing novel devices in nanoscale. It’s still a challenge to induce robust room temperature ferromagnetism in monolayer transition metal dichalcogen compound materials. In this paper, high quality monolayer MoS2 was prepared by chemical vapor deposition and low energy Cu ions were implanted into MoS2 via ion implantation. The surface morphology, chemical states, optical and magnetic properties were systematically investigated. Robust room-temperature ferromagnetism with saturation magnetization as high as 58 μB/Cu (∼2148 emu/cm3) was successfully induced in monolayer MoS2 after Cu implantation. Moreover, the magnetic properties are weakly temperature dependent, which is clearly the characteristic of defect-induced magnetism. First principles density functional theory calculations reveal that various structural defects, including nanohole, CuMo, Cui + VS and CuMo + VS can induce high magnetic moments. Meanwhile, CuMo and Cui + VS have lower formation energies and may contribute significantly to the extremely large magnetism in the implanted monolayer MoS2. Our work has demonstrated that through defects engineering by Cu implantation, robust room temperature ferromagnetism can be achieved in monolayer MoS2, which provides a potential way to induce large magnetization in other transition metal dichalcogen compound materials, and opens up new opportunities for their applications in nano-spintronics.

New nonmagnetic aliovalent dopants (Li+, Cu2+, In3+ and Ti4+): Optical and strong intrinsic room temperature ferromagnetism of perovskite BaSnO3

Nonmagnetic Li+, Cu2+, In3+ and Ti4+ ions were employed to induce robust room temperature ferromagnetism in perovskite BaSnO3 for advanced spintronics applications. New BaSn0.96M0.04O3 (M = Li+, Cu2+, In3+ and Ti4+) compositions were synthesized by modified Pechini method. In all compositions, single phase of cubic BaSnO3 was detected in the XRD patterns without any impurities. The FTIR spectra displayed the distinctive vibrational absorption band of BaSnO3 and verified the absence of any impurities. The SEM images evidently showed a decrement of grain size alongside morphological changes for doped BaSnO3 compositions compared to the pure one. The band gap energy of BaSnO3 was considerably influenced by the incorporation of Li+, Cu2+, In3+ and Ti4+ dopants. BaSn0.96Cu0.04O3 sample exhibited the highest refractive index value and the minimum value was obtained for BaSn0.96Ti0.04O3. Remarkably, at equal concentration two of the used nonmagnetic elements showed the ability to induce room temperature ferromagnetism in BaSnO3 lattice. Herein, BaSn0.96Cu0.04O3 exhibits a robust and symmetrical ferromagnetic hysteresis loop with complete saturation magnetization (Ms) of 0.158 emu/g and coercivity (Hc) of 42 Oe. BaSn0.96Ti0.04O3 composition revealed a ferromagnetic behavior within magnetic field of± 5000 Oe and the trend was reversed for higher values to show a diamagnetic performance. The interaction between the 3d orbitals of Cu2+ (3d9) or Ti4+ (d0) with the trapped electrons in the oxygen vacancies encourage a ferromagnetic coupling in BaSnO3 structure. The outer shell orbitals of Cu2+ and Ti4+ dopants and the oxygen vacancies seem to play a significant role in the magnetic properties.

Room temperature ferromagnetism and transport properties in InN/VTe2 van der Waals heterostructures

The room temperature ferromagnetism can be induced for nonmagnetic pristine graphene-like InN monolayer through establishing van der Waals heterostructure with ferromagnetic semiconductor, which could be applied for realizing novel low-dimensional spintronic devices. Here, we investigate the electronic structure and magnetic properties of InN/VTe2 van der Waals heterostructure under strain and electrostatic doping by first-principles calculations. The InN/VTe2 van der Waals heterostructure possesses desired physical properties such as a symmetric band alignment, ferromagnetic ground state, large in-plane magnetic anisotropy energy of 1.54 meV, and high Curie temperature of 354 K. Meanwhile, the band alignment and magnetic anisotropy energy for InN/VTe2 van der Waals heterostructure can be also tuned effectively by strain. Significant enhancement of conductivity and robust above room temperature ferromagnetism exhibit in InN/VTe2 van der Waals heterostructure under electrostatic doping and paves a new route toward a low-dimensional spintronic field-effect transistor.

Ferromagnetism of Mn-N4 architecture embedded graphene

The realization of intrinsic two-dimensional (2D) magnetic materials with high Curie temperature is one of the prevalent research directions in spintronics. Here, a 2D ferromagnet of Mn-N4 embedded graphene is reported, where the single Mn atom dispersed Mn-N4 structure is confirmed by extended x-ray absorption fine structure and high-angle annular dark-field scanning transmission electron microscopy results. Magnetic measurements demonstrate that the Mn-N4 embedded graphene exhibits robust room-temperature ferromagnetism, and the x-ray magnetic circular dichroism results reveal that the magnetic moments come from the embedded Mn atoms. Furthermore, using first-principle calculations, we demonstrate that the Mn-N4 architecture is the source of the magnetism and the long-range magnetic ordering is favored in such coordination systems.

Magnetic properties in a IIIA-nitride monolayer doped with Ag: A density functional theory investigation

We present a density functional theory study on the electronic structures and magnetism of IIIA-nitride (AlN, GaN and InN) monolayer doped with Ag atoms. The results show that the IIIA-nitride binary compounds doped with low concentrations of Ag atoms are spin-polarized with 2.0 µB. Among them, single layer AlN and GaN doped with Ag atoms both demonstrate two possible ground states: ferromagnetic and antiferromagnetic. In contrast, Ag-doped InN monolayer only exhibits ferromagnetic ground state with half-metallicity. Moreover, different doping concentration of Ag atoms results into various half-metal band-gaps. With increasing the concentration of Ag atoms, the energy gap of corresponding system significantly decreases. Under some suitable concentrations and sites of doped-Ag atoms, robust room-temperature ferromagnetism even can be realized in these systems. The above work shows a rich variety of electronic and magnetic properties in IIIA-nitride monolayer induced by Ag doping, which provides a simple and effective method to design new electronic and spintronic devices based on layered nanomaterials.

Monolayer CeI2 : An intrinsic room-temperature ferrovalley semiconductor

Two-dimensional ferrovalley semiconductors with robust room-temperature ferromagnetism and sizable valley polarization hold great prospects for future miniature information storage devices. As a new member of the ferroic family, however, such ferrovalley materials have rarely been reported. By first-principles calculations, we identify that monolayer $\mathrm{Ce}{\mathrm{I}}_{\text{2}}$ is an intrinsic ferromagnetic semiconductor and exhibits excellent ambient stability, strong easy in-plane magnetocrystalline anisotropy, and a high magnetic transition temperature up to 374 K. The ferromagnetism is found to arise from the hybridization of Ce-$4f/5d$ and I-$5p$ orbitals. When monolayer $\mathrm{Ce}{\mathrm{I}}_{\text{2}}$ is magnetized toward the off-plane $z$ direction, a spontaneous valley polarization as large as 208 meV in the top valence band can be achieved due to the simultaneous breaking of both inversion symmetry and time-reversal symmetry, which is further verified by the perturbation theory of spin-orbital coupling. Also, the anomalous valley Hall effect can be observed under an in-plane electrical field due to the robust valley-contrasting Berry curvature. Overall, the combination of intrinsic semiconducting ferromagnetism and spontaneous valley polarization renders monolayer $\mathrm{Ce}{\mathrm{I}}_{\text{2}}$ a compelling room-temperature ferrovalley semiconductor for potential applications in nanoscale spintronics and valleytronics.

The exchange between anions and cations induced by coupled plasma and thermal annealing treatment for room-temperature ferromagnetism.

Two-dimensional (2D) materials, with outstanding magnetic properties at room temperature, are highly desirable for the future spintronic and nanoscale electronic industry. However, most of the 2D systems are not of magnetic nature due to thermal fluctuations. Herein, we propose a novel strategy to induce robust room-temperature ferromagnetism in the originally nonmagnetic 2D ReS2 by the exchange between anions and cations. The vacancies are created by argon plasma treatment, which lowers the formation energy of point defects. The subsequent annealing facilitates the movement of the cations into the anion sites, giving rise to antisite defects, which leads to a significant increase in the magnetization. First-principles calculations demonstrate that the point defect with respect to the antisite substitution from Re to S is responsible for the extraordinary room-temperature ferromagnetism. This work opens a new door to the design of spin electronic structures by controllable antisite defects.

Atomic origin of room-temperature two-dimensional itinerant ferromagnetism in an oxide-monolayer heterostructure

Materials with room-temperature two-dimensional itinerant ferromagnetism enable ultracompact device density and quantum computing in next-generation nano-spintronics. Among numerous candidates, perovskite-based heterostructures have offered an excellent platform to manipulate spin-orbital-charge coupling, unveiling a series of emergent spin-dependent phenomena. In this work, we have fulfilled a robust room-temperature soft ferromagnetism together with a metallic characteristic based on a high quality SrRuO3-monolayer-based superlattice. Further examination on this short-range ferromagnetism has been carried out by synchrotron-related spectroscopy, where charge-transfer-induced antiferromagnetic coupling between partial Ru and Ti ions have been found. Although such local antiferromagnetic coupling would break long range ferromagnetic order, it simultaneously stabilize the localized intralayer ferromagnetic order in the SrRuO3 monolayers, which is confirmed by theoretical calculations. Our study not only represents a methodological advance of achieving fantastic magnetic properties in functional oxide monolayer, but is promising to unlock new opportunities for oxide-based spintronic devices toward room-temperature applications.

Embedding atomic cobalt into graphene lattices to activate room-temperature ferromagnetism

Graphene is extremely promising for next-generation spintronics applications; however, realizing graphene-based room-temperature magnets remains a great challenge. Here, we demonstrate that robust room-temperature ferromagnetism with TC up to ∼400 K and saturation magnetization of 0.11 emu g−1 (300 K) can be achieved in graphene by embedding isolated Co atoms with the aid of coordinated N atoms. Extensive structural characterizations show that square-planar Co-N4 moieties were formed in the graphene lattices, where atomically dispersed Co atoms provide local magnetic moments. Detailed electronic structure calculations reveal that the hybridization between the d electrons of Co atoms and delocalized pz electrons of N/C atoms enhances the conduction-electron mediated long-range magnetic coupling. This work provides an effective means to induce room-temperature ferromagnetism in graphene and may open possibilities for developing graphene-based spintronics devices.