Net Magnetic Moment Research Articles

Phononic switching of magnetization by the ultrafast Barnett effect.

The historic Barnett effect describes how an inertial body with otherwise zero net magnetic moment acquires spontaneous magnetization when mechanically spinning1,2. Breakthrough experiments have recently shown that an ultrashort laser pulse destroys the magnetization of an ordered ferromagnet within hundreds of femtoseconds3, with the spins losing angular momentum to circularly polarized optical phonons as part of the ultrafast Einstein-de Haas effect4,5. However, the prospect of using such high-frequency vibrations of the lattice to reciprocally switch magnetization in a nearby magnetic medium has not yet been experimentally explored. Here we show that the spontaneous magnetization gainedtemporarily by means of the ultrafast Barnett effect, through the resonant excitation of circularly polarized optical phonons ina paramagnetic substrate, can be used to permanently reverse the magnetic state of a heterostructure mounted atop the said substrate. With the handedness of the phonons steering the direction of magnetic switching, the ultrafast Barnett effect offers a selective and potentially universal method for exercising ultrafast non-local control over magnetic order.

First-Principles prediction of the structural stability, optoelectronic, magnetic properties and mechanical response of olivine type LiMPO4 (M = Ni, Cu) phosphate materials for energy storage applications

The quest for the most suitable materials for energy storage applications is a pressing requirement in the current era of science and technology. In this article, we have performed first-principles calculation based on density functional theory (DFT) utilizing the CASTEP code to analyze LiMPO4 (M = Ni, Cu) for energy storage applications. The computed lattice parameters in the orthorhombic crystal structure for LiNiPO4 are determined to be a = 10.336 Å, b = 6.006 Å, c = 4.693 Å with cell angles α = β = γ = 90o and for LiCuPO4, its values are a = 10.042 Å, b = 6.122 Å, c = 5.123 Å with cell angles α = β = γ = 90o. The calculated negative cohesive energies, −6.21 eV/atom for LiNiPO4 and −6.13 eV/atom for LiCuPO4, confirm their structural stability. The energy band structure demonstrates the semi-metallic characteristics of both LiNiPO4 and LiCuPO4 materials with the energy gap of 1.80 eV and 3.84 eV, respectively. Additionally, both LiNiPO4 and LiCuPO4 exhibit a net magnetic moment of 2 μB. The calculated elastic constants for these materials meet Born’s stability criteria while confirming their mechanical stability and positioning them as highly appropriate materials for energy storage systems. Furthermore, LiNiPO4 and LiCuPO4 showcase remarkable optical conductivity measuring at 4.40 (fs)-1 and 5.24 (fs)-1, respectively, which asserts their suitability for applications in energy storage technology.

The exploration of physical properties of 2D MXenes M3N2 (M= Ti, Hf, Zr, Mo) through the first principles approach: The energy harvesting materials

The worldwide upsurge in energy consumption and its escalating demand day to day are depleting its natural resources. Thus forth, in order to compensate the present scenario and substitute energy harvesting appliances with efficient/cost effective ones, this article discusses 2D MXene materials. Where the structural, optoelectronic, magnetic, and mechanical behavior of pristine M3N2 (M= Ti, Hf, Zr, Mo) MXenes are investigated within the framework of CASTEP modeling and simulation code that is solely based on DFT while utilizing the GGA approach induced by the Perdew–Burke–Ernzerhof (PBE). The crystal structures of these materials are optimized, accordingly, the energy versus volume optimization plots ensure chemically stability of the considered materials. Owing to have an overlapping aptitude of the energy states extant on the Fermi level of the band structures and density of states, these MXenes are declared to be metallic materials that exhibit overall conductive behavior. The elastic parameters explored through Voigt-Reuss-Hill’s approximation endore the mechanical stability of these materials. Finally, in depth magnetic analysis unveils that the MXenes except Mo3N2 fall into antiferromagnetic category whereas Mo3N2 imitates paramagnetic materials with net magnetic moment of 2 μB. Thorough analyses can deduce that the considered MXenes are appealing ones for several energy harvesting optoelectronic applications.

Stoner instability-mediated large magnetoelectric effects in 2D stacking electrides

Strong magnetoelectric effects in single-phase two-dimensional (2D) materials are extremely rare in nature. Here by first-principles calculations, we find a strong magnetoelectric coupling in polar stacking bilayer Hf2S that allows the reversal of net magnetic moments with the reversal of electric dipoles. Further analysis shows that such strong magnetoelectric effects benefit from the Stoner instability of surface Hf atoms triggered by polar stacking. Moreover, an unexpectedly large out-of-plane electric polarization (which is at least two times larger than that of bilayer BN) survives in the material, despite its metallicity. The large electric polarization is ascribed to the delocalized interlayer electrons which generally present in layered electride materials. It is quite interesting that large electric polarization, metallicity and magnetism coexist in one single-phase material. Our findings reveal rich physical phenomena to be explored in 2D stacking multiferroics and suggest an alternative way of searching for strong magnetoelectric materials with ultrathin thickness.

First-Principles Calculations to Investigate Spin-Oriented Magnetic Phases, Band Gaps, Elastic, and Thermodynamic Calculations of VNi2O4

In this study, spin and U-Coulomb interactions-dependent electronic structure, pressure-dependent elastic, and thermodynamics studies of VNi2O4 were performed. The ferromagnetic (FM) phase was the most stable magnetic phase. The lattice parameter was calculated as 8.32 Å. The bulk modules were calculated as 197.695 GPa and 198.038 GPa, respectively, in the initial condition and the elastic calculations, so the initial and elastic conditions were compatible. VNi2O4 material had band gaps of 1.597 eV, 2.159 eV, 2.659 eV, 3.094 eV, 3.439 eV, 3.729 eV, and 3.978 eV in the majority spin electrons in the Generalized Gradient Approximation (GGA), and U-Coulomb interactions (U = 1, 2, 3, 4, 5 and 6 eV), respectively. Hence, it was a true half-metallic ferromagnetic. VNi2O4 was ductile at 0 GPa, with a Debye temperature of 586.596 K. The net magnetic moment of VNi2O4 was 6.00 µB/f.u. As a result, VNi2O4 provides all the necessary conditions for spintronic applications.

Ferromagnetism on an atom-thick & extended 2D metal-organic coordination network

Ferromagnetism is the collective alignment of atomic spins that retain a net magnetic moment below the Curie temperature, even in the absence of external magnetic fields. Reducing this fundamental property into strictly two-dimensions was proposed in metal-organic coordination networks, but thus far has eluded experimental realization. In this work, we demonstrate that extended, cooperative ferromagnetism is feasible in an atomically thin two-dimensional metal-organic coordination network, despite only ≈ 5% of the monolayer being composed of Fe atoms. The resulting ferromagnetic state exhibits an out-of-plane easy-axis square-like hysteresis loop with large coercive fields over 2 Tesla, significant magnetic anisotropy, and persists up to TC ≈ 35 K. These properties are driven by exchange interactions mainly mediated by the molecular linkers. Our findings resolve a two decade search for ferromagnetism in two-dimensional metal-organic coordination networks.

Large Anomalous Hall Effect at Room Temperature in a Fermi‐Level‐Tuned Kagome Antiferromagnet

AbstractThe recent discoveries of surprisingly large anomalous Hall effect (AHE) in antiferromagnets have attracted much attention due to their promising use in spintronics devices. However, such AHE‐hosting antiferromagnetic materials are rare in nature. Herein, it is demonstrated that Mn2.4Ga, a Fermi‐level‐tuned kagome antiferromagnet, has a large anomalous Hall conductivity of ≈150 Ω−1 cm−1 at room temperature that surpasses the usual high values (i.e., 20–50 Ω−1 cm−1) observed so far in two outstanding kagome antiferromagnets, Mn3Sn and Mn3Ge. Although the triangular spin structure of Mn2.4Ga shows a weak net magnetic moment of ≈0.05 µB per formula unit, it guarantees a nonzero Berry curvature in the kagome plane. Moreover, the anomalous Hall conductivity exhibits a sign reversal with the rotation of a small magnetic field that can be ascribed to the field‐controlled chirality of the spin triangular structure. This theoretical calculations further suggest that the large AHE in Mn2.4Ga originates from a significantly enhanced Berry curvature associated with the tuning of the Fermi level close to the Weyl points. These properties, together with the ability to manipulate moment orientations using a moderate external magnetic field, make Mn2.4Ga extremely exciting for future antiferromagnetic spintronics.

Room‐Temperature Macroscopic Ferromagnetism in Multilayered Graphene Oxide

AbstractGraphene has a long spin lifetime and hyperfine interactions, favoring its potential application as spintronics. Despite the recent discoveries of spin‐containing graphene materials, graphene‐based materials with room‐temperature macroscopic ferromagnetism are extremely rare. In this article, room‐temperature ferromagnetic amorphous graphene oxide (GO) is synthesized by introducing abundant oxygen‐containing functional groups and C defects into single‐layered graphene, followed by a self‐assembly process under supercritical CO2 (SC CO2). Such amorphous GO exhibits the highest saturation magnetization (1.71 emu g−1) and remanent magnetization (0.251 emu g−1) compared to the rest of metal‐free graphene‐based materials at room temperature. Experimental and theoretical investigations attribute such strong ferromagnetism to the bridging of the adjacent graphene layers though the out‐of‐plane oxygen‐containing groups, which leads to asymmetric lattices with large net magnetic moments.

Ionic‐Liquid‐Gating‐Induced Hydrogenation in Epitaxial Strontium Ferrite

AbstractIncorporating hydrogen into complex oxides holds promise for discovering exotic phenomena and novel functionalities by promoting couplings between ion and lattice/charge/spin/orbital degrees of freedom. Here, electrolyte gating‐driven hydrogenation is investigated in epitaxial brownmillerite SrFeO2.5 thin films in which the hydrogenation‐induced lattice distortion is qualitatively different from its counterpart SrCoO2.5. The achievable lattice expansion in hydrogenated SrFeO2.5 is weaker than in SrCoO2.5 and primarily occurs along the normal of the stacked octahedral FeO6 and tetrahedral FeO4 layers. Upon the substitution of Fe with Co, the lattice expansion monotonically increases with increase of Co/Fe ratio, implying an intrinsic difference in accommodating hydrogen between Fe‐ and Co‐based brownmillerites. Moreover, a net magnetic moment in hydrogenated SrFeO2.5 films is observed above room temperature, which gradually weakens with the increase of Co substitution, suggesting a stronger canted magnetism in Fe‐based hydrogenated brownmillerites. This work clarifies the electrolyte gating‐driven hydrogenation mechanisms in brownmillerite SrFeO2.5 epitaxial thin films and those with Co substitution, particularly the deterministic role of Co/Fe ratio in the evolution of structure and properties upon hydrogenation.

Emergent Ferromagnetism in CaRuO3/CaMnO3 (111)-Oriented Superlattices.

The boundary between CaRuO3 and CaMnO3 is an ideal test bed for emergent magnetic ground states stabilized through interfacial electron interactions. In this system, nominally antiferromagnetic and paramagnetic materials combine to yield interfacial ferromagnetism in CaMnO3 due to electron leakage across the interface. In this work, we show that the crystal symmetry at the surface is a critical factor determining the nature of the interfacial interactions. Specifically, by growing CaRuO3/CaMnO3 heterostructures along the (111) instead of the (001) crystallographic axis, we achieve a 3-fold enhancement of the magnetization and involve the CaRuO3 layers in the ferromagnetism, which now spans both constituent materials. The stabilization of a net magnetic moment in CaRuO3 through strain effects has been long-sought but never consistently achieved, and our observations demonstrate the importance of interface engineering in the development of new functional heterostructures.

Microwave Field-Induced Changes in Raman Modes and Magnetic Force Images of Antiferromagnetic NiO Films

Effective control of domain walls or magnetic textures in antiferromagnets promises to enable robust, fast, and nonvolatile memories. The lack of net magnetic moment in antiferromagnets implies the need for creative ways to achieve such a manipulation. We conducted a study to investigate changes in magnetic force microscopy (MFM) imaging and in the magnon-related mode in Raman spectroscopy of virgin NiO films under a microwave pump. After MFM and Raman studies were conducted, a combined action of broadband microwave (0.01–20 GHz, power scanned from −20 to 5 dBm) and magnetic field (up to 3 kOe) were applied to virgin epitaxial (111) NiO and (100) NiO films grown on (0001) Al2O3 and (100) MgO substrates, following which the MFM and Raman studies were repeated. We observed a suppression of the magnon-related Raman mode subsequent to the microwave exposure. Based on MFM imaging, this effect appeared to be caused by the suppression of large antiferromagnetic domain walls due to the possible excitation of antiferromagnetic spin oscillations localized within the antiferromagnetic domain walls.

Transport characterization of magnetic phase transition in Mn<sub>3</sub>Sn thin films

In recent years, topological antiferromagnetic material with hexagonal Kagome structure has attracted great research interest due to its unique properties. Although its net magnetic moment is close to zero, the topological antiferromagnet exhibits the strong magnetoelectric, the magneto-optical, and the magnetothermal effect, with a strength comparable to that of ferromagnetic material, which makes it highly valuable for various applications. After several years of extensive studies, it has been realized that most of the unique properties of topological antiferromagnet are actually closely related to its magnetic structure. However, it has been found that the magnetic structure of the material is highly sensitive to its chemical composition and growth condition. Therefore, it is crucial to develop a universal and simple method of measuring the magnetic structure and determining the magnetic phase transition of hexagonal Kagome topological antiferromagnetic material, which can severe as a good supplement for the current high-energy neutron diffraction approach that is not accessible for ordinary laboratories. In this study, we have successfully prepared high-quality (<inline-formula><tex-math id="M3">\begin{document}$ 11\bar{2}0 $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20231766_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20231766_M3.png"/></alternatives></inline-formula>)-oriented hexagonal Kagome antiferromagnetic Mn<sub>3</sub>Sn thin films on (<inline-formula><tex-math id="M4">\begin{document}$1 \bar{1} 02$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20231766_M4.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20231766_M4.png"/></alternatives></inline-formula>)-oriented Al<sub>2</sub>O<sub>3</sub> single crystal substrates by using the pulsed laser deposition method. After systematically measuring how the magnetic and transport properties of the Mn<sub>3</sub>Sn thin film change with temperature, it is found that its magnetization curve, Hall resistivity curve, and magnetoresistance curve exhibit certain anomalous features at some or all of its three magnetic phase transition temperatures. These features can serve as good evidences of magnetic phase transitions in this hexagonal Kagome antiferromagnetic Mn<sub>3</sub>Sn thin film, or even could be used to measure the temperatures of these magnetic phase transitions. Our work contributes to the further advancement of the application of hexagonal Kagome topological antiferromagnetic materials to spin electronic devices.

Magnetic polarons reach a hundred thousand Bohr magnetons.

The ability of light to manipulate fundamental interactions in a medium is central to research in optomagnetism and applications in electronics. A prospective approach is to create composite quasiparticles, magnetic polarons, highly susceptible to external stimuli. To control magnetic and transport properties by weak magnetic and electric fields, it is important to find materials that support photoinduced magnetic polarons with colossal net magnetic moments. Here, we demonstrate that magnetic polarons with a record-high magnetic moment, reaching and exceeding a hundred thousand Bohr magnetons, can be optically generated in EuO, an archetypal ferromagnetic semiconductor. The phenomenon is established employing the photoinduced Faraday effect studied in EuO films by a two-color pump-probe technique. The giant magnetic polarons are generated just above the Curie temperature once EuO is exposed to photons of an energy exceeding the bandgap. Picosecond temporal dynamics of magnetic polarons follows relaxation processes in the spin-split 5d conduction band occupied by the photoexcited electron. The study is expected to provide a platform for implementation of an efficient optical control over the magnetic state in solids.

Orientational ordering and assembly of silica-nickel Janus particles in a magnetic field.

The orientation ordering and assembly behavior of silica-nickel Janus particles in a static external magnetic field were probed by ultra small-angle X-ray scattering (USAXS). Even in a weak applied field, the net magnetic moments of the individual particles aligned in the direction of the field, as indicated by the anisotropy in the recorded USAXS patterns. X-ray photon correlation spectroscopy (XPCS) measurements on these suspensions revealed that the corresponding particle dynamics are primarily Brownian diffusion [Zinn, Sharpnack & Narayanan (2023). Soft Matter, 19, 2311-2318]. At higher fields, the magnetic forces led to chain-like configurations of particles, as indicated by an additional feature in the USAXS pattern. A theoretical framework is provided for the quantitative interpretation of the observed anisotropic scattering diagrams and the corresponding degree of orientation. No anisotropy was detected when the magnetic field was applied along the beam direction, which is also replicated by the model. The method presented here could be useful for the interpretation of oriented scattering patterns from a wide variety of particulate systems. The combination of USAXS and XPCS is a powerful approach for investigating asymmetric colloidal particles in external fields.

First Principles Calculations on the Electronic, Elastic, Structural, and Magnetic Properties of Co2RuGe and Co2NiGe FH Alloys

Utilizing first principles, the structural, elastic, magnetic, and electronic properties of Co2YGe FH (Full-Heusler) alloys where Y is Ni, Ru have been examined. The partial and total densities of states, as well as electronic band structures, have been calculated. The Co2YGe alloys half metallic-nature is confirmed by the computed band structures, which show that the valence and conduction bands in the up spin channel overlap at the Fermi-level while here is a band-gap between them in the down spin channel. These compounds have ½ (half) metallic properties, as seen by the TDOS and PDOS. According to mechanical characteristics, the alloys Co2NiGe and Co2RuGe are highly stiff and they respectively are ductile and brittle. By their magnetic characteristics this is demonstrated that compound have Para magnetism property as their net magnetic moment is not zero. According to the results, these alloys could be a contender for spintronic devices.

First principles study on band gap modulation of TiO2 (112) surface for enhancing optical properties

Anatase TiO2 is widely used in solar photocatalysis. However, the optical properties are limited by its ability to capture visible light and its poor activity. In order to obtain ideal material properties, GGA + U method based on density functional theory is used to study the electronic structure and optical properties of anatase phase TiO2 and its (112) surface and Cr and Co-doped TiO2 (112) surface. The results show that the transition metal Cr-doped system is more stable than the Co-doped system. The four systems exhibit semiconducting properties. The indirect band gap value of intrinsic TiO2 is 3.245 eV, and the impurity bands appear in the spin-up energy bands after Cr, Co doping. The impurity states of the doped system spin split, which transforms the non-magnetic semiconductor into a semiconductor with net magnetic moments of 2 μB and 3 μB, respectively. In addition, the Cr, Co-doped systems show excellent optical properties, and the absorption coefficients are red-shifted in the range of (0–3 eV) with higher optical absorptivities. Through the investigation, it is evident that doping results in different degree of band gap change. As the conduction band moves towards the lower energy level, an impurity band is generated near the Fermi level. The presence of the impurity band fundamentally alters the initial transition mode of the electron, making the transition require less energy, thus enabling enhanced optical properties. The doping system enhances the lepton threshold of electrons and light absorption by changing the mode of inter-band leaps and decreasing the reflectivity, making them candidates in the field of optoelectronics and photocatalysis.

Revealing emergent magnetic charge in an antiferromagnet with diamond quantum magnetometry.

Whirling topological textures play a key role in exotic phases of magnetic materials and are promising for logic and memory applications. In antiferromagnets, these textures exhibit enhanced stability and faster dynamics with respect to their ferromagnetic counterparts, but they are also difficult to study due to their vanishing net magnetic moment. One technique that meets the demand of highly sensitive vectorial magnetic field sensing with negligible backaction is diamond quantum magnetometry. Here we show that an archetypal antiferromagnet-haematite-hosts a rich tapestry of monopolar, dipolar and quadrupolar emergent magnetic charge distributions. The direct read-out of the previously inaccessible vorticity of an antiferromagnetic spin texture provides the crucial connection to its magnetic charge through a duality relation. Our work defines a paradigmatic class of magnetic systems to explore two-dimensional monopolar physics, and highlights the transformative role that diamond quantum magnetometry could play in exploring emergent phenomena in quantum materials.

Insights into the ferromagnetism-antiferromagnetism transition: A first-principles study of LaFexNi1-xO3 (0≤x≤0.5)

The effect of different Fe doping concentration (x = 0.125, 0.25, 0.375 and 0.5) on electronic structure and magnetic properties of LaNiO3 (LNO) have been performed on the spin polarization calculations based on first principles. The calculation results show that with the increase of Fe dopant concentration, LaFexNi1-xO3 undergoes a magnetic transition from ferromagnetism (FM) to antiferromagnetism (AFM). The net magnetic moments of LaFe0.125Ni0.875O3, LaFe0.25Ni0.75O3, LaFe0.375Ni0.625O3 and LaFe0.5Ni0.5O3 in the FM ground state are found to be 12.00 µB/supercell, 16.00 µB/supercell, 20.06 µB/supercell and 23.96 µB/supercell, respectively. In the magnetic configuration of AFM of LaFexNi1-xO3 (x = 0.125 and 0.375) with the nearest doping position, the asymmetric magnetic structure leads to the symmetry of the spin-ordered AFM network is broken, resulting in the generation of net magnetic moment of -3.06 µB and 3.87 µB. The net magnetic moment in LaFexNi1-xO3 mainly originates from transition metals (TM) Fe, Ni and magnetized O atoms.

Magnetic properties of Fe-doped NiO nanoparticles

Undoped and Fe-doped NiO nanoparticles were successfully synthesized using a lyophilization method and systematically characterized through magnetization techniques over a wide temperature range, with varying intensity and frequency of the applied magnetic fields. The Ni1-xFexO nanoparticles can be described by a core-shell model, which reveals that Fe doping enhances exchange interactions in correlation with nanoparticle size reduction. The nanoparticles exhibit a superparamagnetic blocking transition, primarily attributed to their cores, at temperatures ranging from above room temperature to low temperatures, depending on the Fe-doping level and sample synthesis temperature. The nanoparticle shells also exhibit a transition at low temperatures, in this case to a cluster-glass-like state, caused by the dipolar magnetic interactions between the net magnetic moments of the clusters. Their freezing temperature shifts to higher temperatures as the Fe-doping level increases. The existence of an exchange bias interaction was observed, thus validating the core-shell model proposed.

Phase change caused by Jahn-Teller distortion in Ni doped MnCo2O4 spinel

Polycrystalline NixMnCo2−xO4 (x = 0, 0.25, 0.5, 0.75, and 1) powders were produced. The addition of nickel to the MnCo2O4 system modifies the magnetic ion concentration and regulates the Jahn-Teller distortion of the system. We have intended to replace octahedral Co with Ni. Beyond expectation, we found that the different types of Co were replaced by Ni with the doping concentration increasing. When the concentration of Ni doping is low, replacing the non-magnetic octahedral Co3+ (3d6, t2 g6eg0), Ni3+ (3d7, t2 g6eg1) enters octahedral sites. The bond angle between tetrahedral Co and octahedral Mn enlarges and the Neel temperature increases from 164 to 207 K. As Ni enters the octahedral site, the net magnetic moment at low temperature increases, which is believed that the sample exhibits a non-collinear magnetic configuration. As the doping Ni concentration is further increased, Ni2+ (3d8, eg4t2 g4) unexpectedly replaces the tetrahedral Co2+ (3d6, eg4t2 g4). The replacement makes the non-collinear frustrated transition temperature increase from 74 K to 87 K. The interaction between Co2+Tet-Ni3+Oct and Ni3+Oct-Mn3+Oct competes with each other to form a spin frustration at low temperature. An antiferromagnetic-dominated spin-glass phase occurs at low temperatures in the NiMnCoO4 system. The saturation magnetization in the NixMnCo2−xO4 system increases from 0.40 to 0.67 μB/formular (2 K).