Intrinsic Magnetism Research Articles

Antiferromagnetic semiconductor nature in a GeS2 monolayer doped with Mn and Fe transition metals.

The absence of intrinsic magnetism in two-dimensional (2D) materials demands functionalization as necessary for broadening their applications. In this work, doping with transition metals (Mn and Fe) is proposed to modify the electronic and magnetic properties of a GeS2 monolayer. A pristine monolayer is an indirect gap semiconductor with an energy gap of 0.73(1.47) eV computed by using the PBE(HSE06) functional. Significant magnetism with a total magnetic moment of 1.18μB emerges in the GeS2 monolayer upon creating a single Ge vacancy, which is produced mainly by six nearest neighboring S atoms. In this case, the monolayer is metallized with S-px,y states responsible. Similarly, the magnetization of the GeS2 monolayer is also achieved by doping with Mn and Fe atoms with total magnetic moments of 3.00 and 3.78μB, respectively. The calculated band structures imply that the magnetic semiconductor nature with a spin-up/spin-down gap of 0.72/0.53 eV is induced by Mn impurity, while doping with Fe atoms leads to monolayer metallization. Being surrounded by more electronegative S atoms, Mn and Fe impurities lose charge amounts of 1.19 and 1.11e, respectively. Further investigations on spin coupling indicate the antiferromagnetic semiconductor nature in Mn- and Fe-doped systems, regardless of the distance between impurities. Our results provide important insights into the effects of doping into the GeS2 monolayer, which demonstrate that the doped systems hold promise for spintronic applications.

Intrinsic and Defect-related Magnetism of MnBi2Te4(Bi2Te3)n family from the Bulk to Two-dimensional Limit

Abstract The van der Waals MnBi2Te4(Bi2Te3)n family, encompassing MnBi2Te4 (n=0), MnBi4Te7(n=1), MnBi6Te10(n=2), and MnBi8Te13(n=3) etc, has attracted considerable interest owing to its intriguing combination of intrinsic magnetism and non-trivial band topology. This unique blend offers a fertile ground for investigating the engineering of magnetic states and the interplay between magnetism and topology. A comprehensive understanding and manipulation of their magnetic properties in both single-crystal bulk and two-dimensional (2D) forms are imperative for the advancement of applications in quantum technology. This review presents an extensive overview of recent experimental and theoretical inquiries into the magnetic characteristics of MnBi2Te4(Bi2Te3)n (n=0, 1, 2, 3) spanning from the bulk to the 2D realm. It delves into intrinsic and defect-related magnetism and its modulation under diverse external fields. The elucidations provided herein aspire to enhance the understanding of magnetic phenomena in magnetic topological insulators, underscoring the potential for tailoring magnetic states to propel future quantum devices.

Spin-polarized ground states and defect-induced intrinsic magnetism in fully hydrogenated rectangular phosphorene quantum dot

Spin-polarized ground states and defect-induced intrinsic magnetism in fully hydrogenated rectangular phosphorene quantum dot

A Critical Core Size for Dynamo Action at the Galilean Satellites

AbstractGanymede is the only known moon with an active dynamo. No mission has discovered intrinsic magnetism at the other Galilean satellites: Io, Europa, and Callisto. A dynamo requires a large magnetic Reynolds number, which in turn demands, for these moons, a large metallic core that is cooling fast enough for convection. Here we quantify these requirements to construct a regime diagram for the Galilean satellites. We compute the internal heat fluxes that would sustain a dynamo over the wide ranges of plausible radii for their metallic cores. Below a critical radius, no plausible heat flux will sustain a dynamo. Europa likely sits on the opposite side of this limit than Ganymede and Io. We predict that future missions may confirm a small (or absent) core, meaning that Europa could not sustain a dynamo even if its interior were cooling as quickly as Ganymede's core.

Strain-tunable electronic and magnetic properties of two-dimensional CrSBr material

Abstract Two-dimensional (2D) materials, particularly those with intrinsic magnetism, hold promise for next-generation spintronic devices due to their unique electronic and magnetic properties. This study investigates the impact of in-plane uniaxial and biaxial strain on the properties of monolayer CrSBr using density functional theory (DFT) and Monte Carlo (MC) simulations. We demonstrate that strain engineering can effectively modulate the electronic band structure and Curie temperature (Tc) of the CrSBr monolayer. Under uniaxial strains, transitions from indirect to direct bandgaps are observed, enhancing semiconductor characteristics. Importantly, compressive strain along the y-direction significantly increases Tc, potentially approaching room temperature. These findings highlight the role of strain manipulation in tailoring the functionality of 2D magnetic materials, crucial for advancing spintronics and nanoelectronic applications.

Supercritical CO2-Guided Passivation Strategies for Oxygen Vacancy Modulation in LaMnO3.

The development of 2D magnetic materials and the modulation of intrinsic magnetism are essential for the exploration of new materials in the field of information storage. Despite its strong ferromagnetic properties, LaMnO3 is hindered by a high number of oxygen defects, which result in a relatively short lifetime when employed in electronic memory devices. Here the successful transformation of bulk LaMnO3 into a 2D structure using supercritical carbon dioxide.is reported. This technique enables the successful modulation of the magnetic properties of the material. Interestingly, it is found that the oxygen defect is repaired, which is in sharp contrast to conventional perovskites. These promising results demonstrate the potential of using the magnetic properties of LaMnO3, which is of great importance in the context of expanding its application in electronic devices.

Multiprogrammable Anisotropic Soft Material via Magneto‐Orientation of Ferromagnetic Nanoplates

AbstractAnisotropic materials featured with ordered arrangement of sub‐structures are ubiquitous in living organisms, and possess rapidly increasing relevance to emerging technologies in smart materials, soft robotics, flexible displays, and biomedicines. However, the integration and programming of multiple properties into anisotropic materials, which endow themselves with extended intrinsic capabilities and utilities, still remain a challenge. Herein, we report a multi‐programmable anisotropic material by embedding ferromagnetic two‐dimensional nanoplates into hydrogel matrix. The nanoplate exhibits not only a disc‐like non‐isotropic shape, but also an intrinsic easy magnetization axis perpendicular to its basal plane. Using a directional external magnetic field, we can precisely control the orientation of nanoplates inside hydrogel precursor solution and then fix them via photolithographic polymerization, leading to the fabrication of anisotropic hydrogel with on‐demand ordered alignment of nanoplates. Such deliberate arrangement of nanoplates brings in extraordinary optical properties due to birefringence, enabling us to encrypt pattern information into hydrogel materials that is only visible under polarized light. Soft actuators with programmable optical, mechanical and magnetic properties are engineered, which allow to encode diverse deformation and locomotion modes, determine the actuation sites, and monitor the sub‐structural anisotropy all simultaneously, opening new avenues for the design of anisotropic soft materials.

Anisotropic magnetic entropy change and magnetic critical behavior in van der Waals Fe3GaTe2

Fe3GaTe2, with intrinsic magnetism at ambient temperature and high perpendicular magnetic anisotropy, is a promising van der Waals material for 2D-materials-based spintronic devices. Herein, we report the anisotropic magnetocaloric effects and magnetic critical phenomena in Fe3GaTe2 single crystal. Owing to the large anisotropy, magnetic entropy change (−ΔSM) shows anisotropic character with −ΔSMmax of 1.67 J kg−1 K−1 along the c axis and 1.11 J kg−1 K−1 in the ab plane under field change of 5 T. The rotating ΔSM from the ab plane to the c axis reaches 0.67 J kg−1 K−1 at magnetic field of 5 T. By carefully fitting the −ΔSMmax and relative cooling power (RCP), we determine their relationships to be −ΔSMmax∝Hn (n = 0.694(1)) and RCP∝Hm (m = 1.301(3)) for the magnetic field along the c-axis. Further analysis of critical behavior near TC reveals critical exponents β = 0.41(1) at TC = 341.5(1) K, γ = 1.01(1) at TC = 341.6(3) K, and δ = 3.67(15) at TC = 340 K, indicating a three-dimensional complex magnetic exchange.

Development of nanocrystallized magnetoelastic sensors with self-biased effect and improved mass sensitivity

The growing demand for cost-effective and wireless sensing technologies requires the development of simple, efficient and optimized sensors able to accurately detecting external agents. Magnetoelastic resonators represent an alternative to the traditional sensing systems, able to combine all the previously cited factors. Several studies have focused on increasing their sensitivity, in order to make it closer to the market. The present study explores thermal treatments as a novel approach to enhance the sensitivity of magnetoelastic resonators, focusing on the positive impact of crystallization processes induced in magnetoelastic platforms. The experimental results confirm an enhancement of resonant frequency and quality factor of the magnetoelastic platforms as treatment temperature increases. Particularly, the sensor annealed at 550 °C shows an increase of the resonant frequency value of 45 % with respect to the as-quenched platform, being that increase of around 1700 % for the quality factor. In addition, the nanocrystallization induction leads to a self-biased resonance, consequence of the intrinsic magnetization resulting from the crystallization in Fe2B and FeCo phases. Further, the study shows the importance of stability in resonant frequency, emphasizing the potential of the 550 °C-annealed platform for mass sensor applications. Gold deposition experiments reveal the enhanced sensitivity of the sensor annealed at 550 °C of 40 % compared to the as-quenched sensor, as well as an increase of 38 % on its accuracy. These findings represent a significant step forward in the development of magnetoelastic-based mass sensors, highlighting the pivotal role of thermal treatments in optimizing sensitivity for practical and efficient external agents detection systems.

Theoretical investigations of two-dimensional intrinsic magnets derived from transition-metal borides M3B4 (M = Cr, Mn, and Fe)

ABSTRACT Two-dimensional (2D) magnetic materials with high critical temperatures (T C ) and robust magnetic anisotropy energies (MAE) hold significant potential for spintronic applications. However, most of 2D magnetic materials are derived from the van der Waals (vdW) layered bulks, which greatly limits the synthesis of 2D magnetic materials. Here, 2D M3B4 (M = Cr, Mn, and Fe; B = Boron), derived from hexagonal and orthorhombic M3AlB4 phases by selectively etching Al layers, was studied for its structural stability, electronic structure, and magnetic properties. By utilizing ab initio calculations and Monte Carlo simulations, we found that the orthorhombic Cr3B4 shows ferromagnetic (FM) metal and possesses an in-plane magnetic easy axis, while the remaining hexagonal and orthorhombic M3B4 structures exhibit antiferromagnetic (AFM) metals with a magnetic easy axis which is perpendicular to the two-dimensional plane. The critical temperatures of these 2D M3B4 structures are found to be above the 130 K. Notably, the ort-Mn3B4 possesses highest T C (~600 K) and strongest MAE (~220 µeV/atom) among these borides-based 2D magnetic materials. Our findings reveal that the 2D M3B4 compounds exhibit much better resistance to deformation compared to M2B2 MBenes and other 2D magnetic materials. The combination of high critical temperature, robust MAE, and excellent mechanical properties makes 2D Mn3B4 monolayer exhibits a favorable potential for spintronic applications. Our research also sheds light on the magnetic coupling mechanism of 2D M3B4, providing valuable insights into its fundamental characteristics.

Epitaxial growth of quasi-2D van der Waals ferromagnets on crystalline substrates

Intrinsic magnetism in van der Waals materials has instigated interest in exploring magnetism in the 2D limit for potential applications in spintronics and also in understanding novel control of 2D magnetism via variation of layer thickness, gate tunability and magnetoelectric effects. The chromium telluride (CrxTey) family is an interesting subsection of ferromagnetic materials with highTCvalues, also presenting diverse stoichiometry arising from self-intercalation of Cr. Apart from the layered CrTe2system, the other non-layered CrxTeycompounds also offer exceptional magnetic properties, and a novel growth technique to grow thin films of these non-layered compounds offers exciting possibilities for ultra-thin spin-based electronics and magnetic sensors. In this work, we discuss the role of crystalline substrates in chemical vapor deposition growth of non-layered 2D ferromagnets, where the crystal symmetry of the substrate as well as the misfit and strain are the key players governing the growth mechanism of ultra-thin Cr5Te8, a non-layered ferromagnet. The magnetic studies of the as-grown Cr5Te8reveal the signatures of co-existing soft and hard ferromagnetic phases, which makes this system an intriguing system to search for emergent topological phases, such as magnetic skyrmions.

Effective control of magnetism and transport properties of monolayer WV2N4 with two magnetic atomic layers and its van der Waals heterostructure

The large magneto-resistance (MR) effect produced by electric control of the magnetic state for van der Waals (vdW) heterostructures composed of vdW intrinsic magnets holds great significance for low-dissipation spintronic devices. Our first-principles calculations reveal that the proposed monolayer WV2N4 is a ferromagnetic (FM) metal with two magnetic V atomic layers, and the interlayer magnetic coupling between two V atomic layers can be switched from FM to antiferromagnetic coupling by applying a small compressive strain. Interestingly, a large MR ratio of 253% is achieved in the proposed graphite/monolayer WV2N4/graphite vdW heterostructure using a −1.5% compressive strain. Combining the strain-induced change in magnetism of monolayer WV2N4 and the graphite/monolayer WV2N4/graphite vdW heterostructure with the inverse piezoelectricity of piezoelectric materials, a feasible strategy is proposed to achieve electric control of the interlayer magnetic coupling of monolayer WV2N4 in the graphite/monolayer WV2N4/graphite vdW heterostructure clamped by piezoelectric materials by utilizing the inverse piezoelectricity, thereby generating a large MR ratio in the graphite/monolayer WV2N4/graphite vdW heterostructure clamped by the piezoelectric material. Our work presents a promising avenue for developing energy-efficient spintronic devices.

Half‐Metallic Ferromagnetism in 2D Janus Monolayers: Mn2GeX (X = As, Sb)

Two‐dimensional (2D) Janus materials are a fascinating class of materials resulting from their unique electronic and magnetic properties induced by mirror symmetry breaking. However, 2D Janus materials with intrinsic magnetism remain rather rare, casting a mysterious veil over magnetism. In this work, the electronic and magnetic properties of Janus Mn2GeX (X = As, Sb) monolayers using the first‐principles calculations are investigated. The results demonstrate that these Janus materials exhibit excellent mechanical and dynamic stability, indicating their potential for future applications in nanoscale spintronic devices. Interestingly, the Janus and monolayers possess exciting half‐metallic character with wide half‐metallic gaps of 0.29 and 0.18 eV, and spin gaps of 1.68 and 1.62 eV, respectively. Their calculated ground state exhibits a strong preference for ferromagnetic ordering, with a Curie temperature () of 630 and 590 K, respectively. Additionally, the ferromagnetism of Janus Mn2GeX (X = As, Sb) monolayers is robust against biaxial strain ranging from −6% to 6%. Under 6% tensile strain, the calculated of the monolayer is 639 K, which represents a 9% increase compared to the observed in the unstrained condition. All these intriguing electronic and magnetic properties make the Janus Mn2GeX (X = As, Sb) monolayers an appealing candidate for applications in nanoscale spintronic devices.

Magnetic tunnel junction based on bilayer LaI2 as perfect spin filter device

The discovery of van der Waals intrinsic magnets has expanded the possibilities of realizing spintronics devices. We investigate the transmission, tunneling magnetoresistance ratio, and spin injection efficiency of bilayer LaI2 using a combination of first-principles calculations and the non-equilibrium Green’s function method. Multilayer graphene electrodes are employed to build a magnetic tunnel junction with bilayer LaI2 as ferromagnetic barrier. The magnetic tunnel junction turns out to be a perfect spin filter device with an outstanding tunneling magnetoresistance ratio of 653% under a bias of 0.1 V and a still excellent performance in a wide bias range. In combination with the obtained high spin injection efficiency this opens up great potential from the application point of view.

Microwave susceptibility analysis of ultrafast moment dynamics in a multicore magnetic nanoparticle system

Room-temperature magnetization dynamics of multicore magnetic nanoparticles often account for intrinsic dipolar magnetism to behave as a single macrospin at low-frequency regime. Either magnetic particle imaging or hyperthermia benefits from the resulting superparamagnetism in terms of nonlinear magnetization response and relaxation losses at frequencies where the rotation of magnetic moments dominates over Brownian motion for a given sinusoidal field. For this situation, spontaneous thermal relaxation (in the absence of external fields) of each composing particle moment within the cluster is critical to define effective Néel time constant and may intersect with ferromagnetic resonance (FMR) at GHz range. Here, we performed broadband AC susceptometry on both immobilized single-core and multicore iron-oxide nanoparticles up to 26.5GHz under DC bias fields. For each solid sample, we confirmed FMR frequency, where large single-core nanoparticle systems demonstrated typical resonance blueshift as DC field increased. Interestingly, high DC field induced the secondary satellite peak in the imaginary part of AC susceptibility spectra for the case of multicore nanoparticle systems. We further highlighted that a synchronous precession of the polarized macrospins under nonuniform effective fields was responsible for splitting FMR peaks at nearby microwave frequencies. Upon curve fitting of the field-dependent FMR frequency spectra, the Landau-Lifshitz-Gilbert-Kittel model later elaborates on the complex moment dynamics of multicore nanoparticle systems in correlation with distribution functions. Published by the American Physical Society 2024

The intrinsic ferromagnetic half-metals with high Curie temperature of tetragonal XCrS4 (X=Ti, Zr) monolayer

Two-dimensional intrinsic magnetic materials with a high Curie temperature (TC) and 100% spin-polarization are highly desirable for creating spintronic devices. In this work, the electronic structure and intrinsic magnetism of XCrS4 (X = Ti, Zr) monolayers are predicted by using first-principles calculations. XCrS4 (X = Ti, Zr) monolayer materials exhibit excellent dynamical, thermal, and dynamically stable stability and small binding energy. The band structures show that XCrS4 (X = Ti, Zr) monolayers are intrinsic ferromagnetic (FM) half-metals with wide half-metallic gaps. Monte Carlo simulations based on the Heisenberg model are used to estimate the Curie temperature (TC) of the TiCrS4 (73 K) and ZrCrS4 (216 K) monolayers. The magnetic performances can be significantly modulated by strain; the TiCrS4 monolayer can undergo FM to antiferromagnetic phase transition under certain uniaxial and biaxial strains. The results indicate that the intrinsic half-metals with higher TC and controllable magnetic properties make XCrS4 (X = Ti, Zr) monolayers enrich the application of nanoscale spintronic devices.

Spin magnetotransport in rare-earth iron garnet (REIG)/Pt: Effects of modulated bulk and REIG/Pt interfaces

The intrinsic magnetization compensation behaviors of rare-earth iron garnets (REIGs) make the material promising for applications in ultrafast spin storage devices. REIG/heavy metal heterostructures such as TbIG/Pt often display two sign crossovers of anomalous Hall effect resistance with varying temperatures. One of these crossovers is attributed to the magnetization compensation of REIG, and the other to the competition between the magnetic proximity effect and the spin Hall effect. Here, we design trilayer REIG heterostructures based on two rare-earth species (Tb and Eu). We modulate the layer stacking of the TbIG/EuIG/TbIG sandwich with a fixed total thickness and explore the contributions of REIG bulk and REIG/Pt interfaces on these two crossover points. As TbIG gradually moves away from Pt, the compensation temperature shows some fluctuations. However, when TbIG is entirely out of contact with Pt, the second crossover point undergoes a change that shows REIG/Pt interface dependency. The results highlight the dominance of REIG bulk on the compensation behavior and the interface sensitivity of the second crossover point. This study provides a reference for designing controllable spintronics devices, such as magnon valve applications.

Electronic, magnetic and catalytic of the Janus monolayer transition-metal trichalcogenides

Nowadays, a booming research direction goes toward the newly two-dimensional (2D) layered materials known as metal phosphorus trichalcogenides, which have intrinsic magnetism. Janus 2D materials with mirror asymmetry display novel properties, providing great promise for application in sensors, catalysis, and electronics devices. Herein, the magnetic, electronic as well as the catalytic properties of Janus MPS1.5Se1.5 (M = Mn, Fe, Ni) monolayer trichalcogenides are systematically studied based on the first-principles calculations. We find that all the three Janus MPS1.5Se1.5 possess antiferromagnetic order, however with different antiferromagnetic configurations. Strain-driven magnetic phase transitions are found in FePS1.5Se1.5. Electronic calculations reveal that all the Janus MPS1.5Se1.5 (M = Mn, Fe, Ni) are semiconductors and the band gaps can be tuned by biaxial strain. We further show that the Janus FePS1.5Se1.5 with optima hydrogen adsorption free energy and good conductivity may be potential candidate for HER electrocatalyst.

Two-dimensional Mo decorated borophenes: high critical temperature, large magnetic anisotropy, and stacking-dependent magnetism

Two-dimensional magnetic materials with high critical temperature, large magnetic anisotropy energy and intrinsic magnetism hold great promise for advancements in spintronics. However, synergizing these attributes within a single material remains challenging. Through the application of swarm-intelligence-based structure searching along with first-principles calculations, we identify two Mo decorated borophene variants, denoted as MoB4 and MoB6, are such candidates with high thermal and dynamical stabilities. MoB4 and MoB6 are characterized as either ferromagnetic or antiferromagnetic metals. Notably, both MoB4 and MoB6 display sizable magnetic anisotropy energy—924 and 932 μeV per Mo atom, respectively—surpassing that of the widely studied CrI3 monolayer, which measures 685 μeV per Cr atom. Monte Carlo simulation suggests the Curie temperature of MoB4 sheet is 390 K, which is above room temperature. Our examination uncovers that bilayer Mo x B y formations exhibit layer-specific van der Waals interactions, contrasting with bilayer borophenes produced experimentally, which display robust interlayer chemical bonding. We determine that the stacking order profoundly influence both the magnetic anisotropy energy and critical temperatures of the material. Specifically, the magnetic anisotropy energy for both structures doubles in their bilayer configurations, with AB-stacked MoB4 and AC-stacked MoB6 demonstrating critical temperatures of 550 K and 320 K, respectively. The exceptional electronic and magnetic characteristics of the Mo x B y monolayers position them as favorable candidates for future spintronic devices.

Multiferroic neuromorphic computation devices

Neuromorphic computation is based on memristors, which function equivalently to neurons in brain structures. These memristors can be made more efficient and tailored to neuromorphic devices by using ferroelastic domain boundaries as fast diffusion paths for ionic conduction, such as of oxygen, sodium, or lithium. In this paper, we show that the local memristor generates a second, unexpected feature, namely, weak magnetic fields that emerge from moving ferroelastic needle domains and vortices. The vortices appear near ferroelastic “junctions” that are common when the external stimulus is a combination of electric fields and structural phase transitions. Many ferroelastic materials show such phase transitions near room temperatures so that device applications display a “multiferroic” scenario where the memristor is driven electrically and read magnetically. Our computer simulation study of an elastic spring model suggests magnetic fields in the order of 10−7 T, which opens the way for a fundamentally new way of running neuromorphic devices. The magnetism in such devices emerges entirely from intrinsic displacement currents and not from any intrinsic magnetism of the material.