Low-dimensional Magnetic Materials Research Articles

Unified transmission electron microscopy with the glovebox integrated system for investigating air-sensitive two-dimensional quantum materials.

Transmission electron microscopy (TEM) is an indispensable tool for elucidating the intrinsic atomic structures of materials and provides deep insights into defect dynamics, phase transitions, and nanoscale structural details. While numerous intriguing physical properties have been revealed in recently discovered two-dimensional (2D) quantum materials, many exhibit significant sensitivity to water and oxygen under ambient conditions. This inherent instability complicates sample preparation for TEM analysis and hinders accurate property measurements. This review highlights recent technical advancements to preserve the intrinsic structures of water- and oxygen-sensitive 2D materials for atomic-scale characterizations. A critical development discussed in this review is implementing an inert gas-protected glovebox integrated system (GIS) designed specifically for TEM experiments. In addition, this review emphasizes air-sensitive materials such as 2D transition metal dichalcogenides, transition metal dihalides and trihalides, and low-dimensional magnetic materials, demonstrating breakthroughs in overcoming their environmental sensitivity. Furthermore, the progress in TEM characterization enabled by the GIS is analyzed to provide a comprehensive overview of state-of-the-art methodologies in this rapidly advancing field.

Significant magnon contribution to heat transfer in nickel nanowires

Magnons, quantized spin waves arising from collective excitations of spins, are typically considered negligible contributors to heat transfer. However, recent studies on low-dimensional magnetic materials have challenged this notion, revealing significant magnon-mediated heat transport. The underlying physics behind this phenomenon, however, remains poorly understood. In this study, we observed a significant reduction in heat transfer in nickel nanowires under the influence of a magnetic field. Our theoretical model revealed a substantial magnon contribution of up to 30 % to nanowire heat transfer. The reduction in heat transfer under a magnetic field stemmed from a drastic decrease in the magnon mean free path (MFP). This decrease in MFP was primarily attributed to suppressing long wavelength magnons with a longer MFP. Our findings provide deeper insights into heat transfer mechanisms in nanoscale ferromagnetic materials and offer valuable guidance for the design of future spintronic devices.

Theoretical Study of the Magnetic Mechanism of a Pca21 C4N3 Monolayer and the Regulation of Its Magnetism by Gas Adsorption.

For metal-free low-dimensional ferromagnetic materials, a hopeful candidate for next-generation spintronic devices, investigating their magnetic mechanisms and exploring effective ways to regulate their magnetic properties are crucial for advancing their applications. Our work systematically investigated the origin of magnetism of a graphitic carbon nitride (Pca21 C4N3) monolayer based on the analysis on the partial electronic density of states. The magnetic moment of the Pca21 C4N3 originates from the spin-split of the 2pz orbit from special carbon (C) atoms and 2p orbit from N atoms around the Fermi energy, which was caused by the lone pair electrons in nitrogen (N) atoms. Notably, the magnetic moment of the Pca21 C4N3 monolayer could be effectively adjusted by adsorbing nitric oxide (NO) or oxygen (O2) gas molecules. The single magnetic electron from the adsorbed NO pairs with the unpaired electron in the N atom from the substrate, forming a Nsub-Nad bond, which reduces the system's magnetic moment from 4.00 μB to 2.99 μB. Moreover, the NO adsorption decreases the both spin-down and spin-up bandgaps, causing an increase in photoelectrical response efficiency. As for the case of O2 physisorption, it greatly enhances the magnetic moment of the Pca21 C4N3 monolayer from 4.00 μB to 6.00 μB through ferromagnetic coupling. This method of gas adsorption for tuning magnetic moments is reversible, simple, and cost-effective. Our findings reveal the magnetic mechanism of Pca21 C4N3 and its tunable magnetic performance realized by chemisorbing or physisorbing magnetic gas molecules, providing crucial theoretical foundations for the development and utilization of low-dimensional magnetic materials.

Bottom-up building of two-dimensional magnetic materials with self-assembly of superatom TM@Sn12 (TM = Sc, Ti, V, Cr, Mn, Fe) clusters

The miniaturization of electronic devices is increasingly requiring some low-dimensional magnetic materials with excellent properties, so ultra-thin two-dimensional magnetic materials have attracted extensive attention. However, most two-dimensional materials exfoliated from bulk either lack intrinsic magnetism or have low magnetic transition temperatures, which greatly limits their practical applications. Here, using magnetic superatom TM@Sn12 (TM = Sc, Ti, V, Cr, Mn, Fe) clusters as building blocks, a series of two-dimensional materials are designed and the underlying mechanism for magnetic order and stability are explained by direct exchange of outer superatom orbitals (1G, 2P and 2D). The honeycomb lattice of TM@Sn12 (TM = V, Cr, Fe) and the square lattice of Ti@Sn12 are ferromagnetic. The Cr@Sn12 honeycomb lattice has a large out-of-plane magnetic anisotropic energy of 2.21 meV and its Curie temperature reaches 162 K, while the Fe@Sn12 honeycomb lattice has a large in-plane magnetic anisotropic energy of 3.58 meV. This research provides a new avenue for developing novel magnetic materials with excellent properties.

Quantum magnetic phenomena in engineered heterointerface of low-dimensional van der Waals and non-van der Waals materials.

Investigating magnetic phenomena at the microscopic level has emerged as an indispensable research domain in the field of low-dimensional magnetic materials. Understanding quantum phenomena that mediate the magnetic interactions in dimensionally confined materials is crucial from the perspective of designing cheaper, compact, and energy-efficient next-generation spintronic devices. The infrequent occurrence of intrinsic long-range magnetic order in dimensionally confined materials hinders the advancement of this domain. Hence, introducing and controlling the ferromagnetic character in two-dimensional materials is important for further prospective studies. The interface in a heterostructure significantly contributes to modulating its collective magnetic properties. Quantum phenomena occurring at the interface of engineered heterostructures can enhance or suppress magnetization of the system and introduce magnetic character to a native non-magnetic system. Considering most 2D magnetic materials are used as stacks with other materials in nanoscale devices, the methods to control the magnetism in a heterostructure and understanding the corresponding mechanism are crucial for promising spintronic and other functional applications. This review highlights the effect of electric polarization of the adjacent layer, changed structural configuration at the vicinity of the interface, natural strain induced by lattice mismatch, and exchange interaction in the interfacial region in modulating the magnetism of heterostructures of van der Waals and non-van der Waals materials. Further, prospects of interface-engineered magnetism in spin-dependent device applications are also discussed.

Metal-Mediated Directional Capping of Rod-Packing Metal-Organic Frameworks.

Two new rod-packing metal-organic frameworks (RPMOF) are constructed by regulating the in situ formation of the capping agent. In CPM-s7, carboxylate linkers extend 1D manganese-oxide chains in four additional directions, forming 3D RPMOF. The substitution of Mn2+ with a stronger Lewis acidic Co2+ , leads to an acceleration of the hydrolysis-prone sulfonate linker, resulting in presence of sulfate ions to reduce two out of the four carboxylate-extending directions, and thus forming a new 2D rod-packing CPM-s8. Density functional theory calculations and magnetization measurements reveal ferrimagnetic ordering of CPM-s8, signifying the potential of exploring 2D RPMOF for effective low-dimensional magnetic materials.

Perfect spin filtering of T-shaped device based on the zigzag silicon carbide nanoribbons

How to generate stable and pure spin-polarized current in nanodevice based on low-dimensional magnetic materials and systems has attracted extensive attention. In this work, using the non-equilibrium Green’s function (NEGF) combined with density-functional theory (DFT), we predict highly conductive transport and perfect spin filtering of the novel T-shaped device, which is constructed by a finite armchair silicon carbide nanoribbon (ASiCNR) connected to one edge of an infinite zigzag silicon carbide nanoribbon (ZSiCNR). This particular performance is due to the fact that there are always two edge states contributing to electron transport around the Fermi level, no matter whether the ZSiCNR is in the ferromagnetic or anti-ferromagnetic state. As a consequence, the T-shaped device would ideally yield 100% spin-polarized current with one spin channel blocked by the ASiCNR part. Moreover, it is found that such blocking effect is independent of the shape of the ASiCNR part. Based on the above analysis, it is easily predicted that such pure spin-polarized current could also be obtained in the device constructed by ZSiCNRs, as long as one pristine edge of ZSiCNRs is defected by doping, absorbing, vacancies and so on, which opens new possibility of two dimensional silicon carbide in spintronic device applications.

Research of Low-Dimensional Carbon-Based Magnetic Materials

Research of Low-Dimensional Carbon-Based Magnetic Materials

Generation and Control of Terahertz Spin Currents in Topology-Induced 2D Ferromagnetic Fe3 GeTe2 |Bi2 Te3 Heterostructures.

Future information technologies for low-dissipation quantum computation, high-speed storage, and on-chip communication applications require the development of atomically thin, ultracompact, and ultrafast spintronic devices in which information is encoded, stored, and processed using electron spin. Exploring low-dimensional magnetic materials, designing novel heterostructures, and generating and controlling ultrafast electron spin in 2D magnetism at room temperature, preferably in the unprecedented terahertz (THz) regime, is in high demand. Using THz emission spectroscopy driven by femtosecond laser pulses, optical THz spin-current bursts at room temperature in the 2D van der Waals ferromagnetic Fe3 GeTe2 (FGT) integrated with Bi2 Te3 as a topological insulator are successfully realized. The symmetry of the THz radiation is effectively controlled by the optical pumping incidence and external magnetic field directions, indicating that the THz generation mechanism is the inverse Edelstein effect contributed spin-to-charge conversion. Thickness-, temperature-, and structure-dependent nontrivial THz transients reveal that topology-enhanced interlayer exchange coupling increases the FGT Curie temperature to room temperature, which provides an effective approach for engineering THz spin-current pulses. These results contribute to the goal of all-optical generation, manipulation, and detection of ultrafast THz spin currents in room-temperature 2D magnetism, accelerating the development of atomically thin high-speed spintronic devices.

CrSbSe3 : A pseudo one-dimensional ferromagnetic semiconductor

Low-dimensional magnetic materials have attracted much attention due to their novel properties and high potential for spintronic applications. In this work, we study the electronic structure and magnetic properties of the pseudo one-dimensional compound CrSbSe$_3$, using density functional calculations, superexchange model analyses, and Monte Carlo simulations. We find that CrSbSe$_3$ is a ferromagnetic (FM) semiconductor with a band gap of about 0.65 eV. The FM couplings within each zig-zag spin chain are due to the Cr-Se-Cr superexchange with the near-90$^\circ$ bonds, and the inter-chain FM couplings are one order of magnitude weaker. By inclusion of the spin-orbit coupling (SOC) effects, our calculations reproduce the experimental observation of the easy magnetization $a$ axis and the hard $b$ axis (the spin-chain direction), with the calculated moderate magnetic anisotropy of 0.19 meV/Cr. Moreover, we identify the nearly equal contributions from the single ion anisotropy of Cr, and from the exchange anisotropy due to the strong SOC of the heavy elements Sb and Se and their couplings with Cr. Using the parameters of the magnetic coupling and anisotropy from the above calculations, our Monte Carlo simulations yield the Curie temperature $T_{\rm{C}}$ of 108 K.

Unraveling Dissipation-Related Features in Magnetic Imaging by Bimodal Magnetic Force Microscopy

Magnetic Force Microscopy (MFM) is the principal characterization technique for the study of low-dimensional magnetic materials. Nonetheless, during years, the samples under study was limited to samples in the field of data storage, such as longitudinal hard disk, thin films, or patterned nanostructures. Nowadays, thanks to the advances and developments in the MFM modes and instrumentation, other fields are emerging like skyrmionic structures, 2D materials or biological samples. However, in these experiments artifacts in the magnetic images can have strong impact and need to be carefully verified for a correct interpretation of the results. For that reason, in this paper we will explore new ideas combining the multifrequency modes with the information obtained from the experimental dissipation of energy associated to tip-sample interactions.

Theoretical investigation on the magnetic properties of Cr2Zn10Se12 and C/N co-doped Cr2Zn10CSe11/Cr2Zn10NSe11 nanoclusters

To search for stable structural units of low dimensional dilute magnetic semiconductor materials, Cr-doped and C/N co-doped Zn12Se12 clusters were investigated with first principle all electron calculations. In geometry-optimized Cr2Zn10Se12 nanoclusters, two Cr atoms substituted the nearest Zn atom sites in the rhombus part. Energy analysis indicated that the ground state of Cr2Zn10Se12 nanoclusters tends to be a weak ferromagnetic coupling state originating from the electron hybridization of the Cr-3d, Cr-4s and Se-4p orbitals. In C/N co-doped Cr2Zn10CSe11/Cr2Zn10NSe11 nanoclusters, the C/N atoms prefer to occupy the Se atom sites to form Cr-C-Cr/Cr-N-Cr bonding. The ground state tends to be a slightly stronger ferromagnetic coupling state, with Cr-3d and C/N-2p orbitals being the main contributors to the magnetism of the nanoclusters. With the introduction of C/N co-doped atoms, the strong electron hybridization among C/N-2p, Cr-3d and Cr-4s orbitals contributed to the enhanced stability of ferromagnetic ground state. For all the Cr2Zn10Se12 and C/N co-doped Cr2Zn10CSe11/Cr2Zn10NSe11 nanoclusters, hole-mediated ferromagnetic coupling between Cr atoms was found to improve the ferromagnetic stability, which may provide some guidance for the exploration of new materials.

Electric-Field Tunable Magnetism in van der Waals Bilayers with A-Type Antiferromagnetic Order: Unipolar versus Bipolar Magnetic Semiconductor

Uncovering the physics behind the electrical manipulation of low-dimensional magnetic materials remains a fundamental issue in practical application of nanoscale spintronics. Here, we propose a strategy to transform A-type antiferromagnetic (AFM) semiconductors into asymmetric AFM unipolar or bipolar magnetic semiconductors by applying perpendicular electric fields in van der Waals bilayer systems. Electric fields lifting energy levels of electrons within same spin channel from consistent layers in opposite direction enables unipolar magnetic semiconductor, whereas electrons within opposite spin channel enable bipolar magnetic semiconductor. A comprehensive study demonstrates this discrepancy originates from spatial distributions of spin density of valence band and conduction band edges in two layers of systems. The electric field induced unipolar or bipolar magnetic semiconducting behavior represents great potential of nanoscale AFM spintronics for information storage and processing.

Tunable Single-Ion Anisotropy in Spin-1 Models Realized with Ultracold Atoms.

Mott insulator plateaus in optical lattices are a versatile platform to study spin physics. Using sites occupied by two bosons with an internal degree of freedom, we realize a uniaxial single-ion anisotropy term proportional to (S^{z})^{2} that plays an important role in stabilizing magnetism for low-dimensional magnetic materials. Here we explore nonequilibrium spin dynamics and observe a resonant effect in the spin alignment as a function of lattice depth when exchange coupling and on-site anisotropy are similar. Our results are supported by many-body numerical simulations and are captured by the analytical solution of a two-site model.

Layer-Dependent Magnetism in Two-Dimensional Transition-Metal Chalcogenides MnTn + 1 (M = V, Cr, and Mn; T = S, Se, and Te; and n = 2, 3, and 4)

Low-dimensional magnetic materials with high stabilities and outstanding magnetic properties are essential for the next generation of spintronic devices. We will discuss the intrinsic magnetism in ...

Interfacial Roughness Facilitated by Dislocation and a Metal-Fuse Resistor Fabricated Using a Nanomanipulator.

Granular magnetic systems consisting of magnetic nanoparticles embedded in a nonmagnetic metallic matrix have emerged as an attractive building block for nanodevices. A key challenge for building interface-based nanodevice applications, such as magnetic memory devices, is to clearly know about the influences of interfacial roughness on the scattering of conduction electrons. Here, we demonstrate a granular magnetic system composed of Co and Cu nanoparticles and further link the atomic structure of the Co/Cu interface to the scattering mechanism of conduction electrons. The multiple scattering is caused by the dislocations at the rough interface, which lead to a reduction of conduction efficiency and an increase of energy consumption. These dislocations mostly originate from the lattice defects on the surface of nanoparticles, the lattice mismatch of two crystal structures, and the different surface energies. Based on the negative effects of a rough interface on electronic transport, we first develop a nanometal-fuse resistor, which could hopefully be used in the protection circuits of nanodevices. Our results may open up the possibility of implementing the low-dimensional granular magnetic materials in nanodevice applications.

Nanocrystallization in FINEMET-Type Fe73.5Nb3Cu1Si13.5B9 and Fe72.5Nb1.5Mo2Cu1.1Si14.2B8.7 Thin Films.

A growing variety of microelectronic devices and magnetic field sensors as well as a trend of miniaturization demands the development of low-dimensional magnetic materials and nanostructures. Among them, soft magnetic thin films of Finemet alloys are appropriate materials for sensor and actuator devices. Therefore, one of the important directions of the research is the optimization of thin film magnetic properties. In this study, the structural transformations of the Fe73.5Nb3Cu1Si13.5B9 and Fe72.5Nb1.5Mo2Cu1.1Si14.2B8.7 films of 100, 150 and 200 nm thicknesses were comparatively analyzed together with their magnetic properties and magnetic anisotropy. The thin films were prepared using the ion-plasma sputtering technique. The crystallization process was studied by certified X-ray diffraction (XRD) methods. The kinetics of crystallization was observed due to the temperature X-ray diffraction (TDX) analysis. Magnetic properties of the films were studied by the magneto-optical Kerr microscopy. Based on the TDX data the delay of the onset crystallization of the films with its thickness decreasing was shown. Furthermore, the onset crystallization of the 150 and 200 nm films began at the temperature of about 400–420 °C showing rapid grain growth up to the size of 16–20 nm. The best magnetic properties of the films were formed after crystallization after the heat treatment at 350–400 °C when the stress relaxation took place.

Resonant Magnetic Induction Tomography of a Magnetized Sphere

We demonstrate the structural imaging of magnetostatic spin-wave modes hosted in a millimeter-sized ferromagnetic sphere. Unlike for low-dimensional magnetic materials, there is no prior technique to image these modes in bulk magnetized solid of revolution. Based on resonant magnetic induction tomography in the microwave range, our approach ensures the robust identification of these non-trivial spin-wave modes by establishing their azimuthal and polar dependences, starting point of magnonic fundamental studies and hybrid systems with complex spin textures well beyond the uniform precession mode.

Ultrafine FeCo Nanoparticles Isolated by Ultrathin Dielectric Shells for Microwave Application

Low-dimensional soft magnetic materials are technologically important for miniaturization of magnetic devices. It is, however, challenging to maintain ferromagnetic response in nanosized magnetic material. In this work, ultrafine FeCo nanoparticles have been prepared by reactive pulsed laser deposition, which can be exchange coupled through ultrathin dielectric shells, even though their diameters are far below the superparamagnetic blocking limit. This unique core/shell structure guarantees ferromagnetic coupling and insulation of neighboring magnetic nanoparticles simultaneously. The nanoparticle film exhibits large saturation magnetization of 1.13 T, high electrical resistivity of 4200 μΩ·cm, maximum permeability of 120, a cutoff frequency of 1.7 GHz, and it is a promising material for microwave application.

Chiral Orbital Magnetism of p-Orbital Bosons in Optical Lattices.

Chiral magnetism is a fascinating quantum phenomena that has been found in low-dimensional magnetic materials. It is not only interesting for understanding the concept of chirality, but also important for potential applications in spintronics. Past studies show that chiral magnets require both a lack of inversion symmetry and spin-orbit coupling to induce the Dzyaloshinskii-Moriya interaction. Here we report that the combination of inversion symmetry breaking and quantum degeneracy of orbital degrees of freedom will provide a new paradigm to achieve chiral orbital magnetism. By means of density matrix renormalization group calculation, we demonstrate that chiral orbital magnetism can be found when considering bosonic atoms loaded in the p band of an optical lattice in the Mott regime. The high tunability of our scheme is also illustrated through simply manipulating the inversion symmetry of the system for cold atom experimental conditions.