Antiferromagnetic State Research Articles

Unexpected band structure changes within the higher-temperature antiferromagnetic state of CeBi

The interest in the rare-earth monopnictides was boosted after the discovery of unconventional surface-state pairs in antiferromagnetically ordered NdBi. In contrast to other materials in which such states were reported, CeBi is known to have multiple antiferromagnetic phases. In this study, we perform angle-resolved photoemission spectroscopy (ARPES) measurements in conjunction with density functional theory (DFT) calculations to investigate the evolution of the electronic structure of CeBi upon a series of antiferromagnetic (AFM) transitions. We find evidence for a new AFM transition in addition to two previously known from transport studies. We demonstrate the development of an additional Dirac state in the ( + − + − ) ordered phase and a transformation of unconventional surface-state pairs in the ( + + − − ) ordered phase. This revises the phase diagram of this intriguing material, where there are now three distinct AFM states below TN in zero magnetic field instead of two as it was previously thought.

Effects of Lu-doping on the magnetic behaviour and ordering of (Ho[formula omitted]Lu[formula omitted])2Fe2Si2C

We have investigated the effects of Lu substitution on the magnetic behaviour and ordering of (Ho1−xLux)2Fe2Si2C (x = 0.32 and 0.46) by high-resolution neutron powder diffraction, magnetisation and specific heat over the temperature range 2 to 300 K. Our study has establised that the antiferromagnetic (AFM) state is weakened upon Lu substitution and that the Néel temperature TN shifts towards lower temperature with increasing Lu content. The replacement of the magnetic Ho3+ ion by the non-magnetic Lu3+ ion of smaller atomic radius, leads to a modification of the crystal field levels, as indicated by the specific heat measurements. Neutron diffraction data analysis reveals that the magnetic structure of undoped Ho2Fe2Si2C, which exhibits a commensurate, antiferromagnetic ordering of the Ho sublattice along the b-axis with a propagation vector k = [0, 0, 12], is maintained in the Lu-doped (Ho1−xLux)2Fe2Si2C compounds.

Synthesis and Characterisation of Vanadium(III) Fluorides α-BaVF5 and BaV(F,OH)5 with an S = 1 Spin Chain Structure

Two new vanadium(III) fluorides, α-BaVF5 and BaV(F,OH)5, were hydrothermally synthesised. The crystal structures of both α-BaVF5 and BaV(F,OH)5 contain chain structures consisting of corner-sharing VIIIF6 or VIII(F,OH)6 octahedra. A monomeric cis-chain structure is found in α-BaVF5, in contrast to the helical-chain structure in BaV(F,OH)5. Although predominantly antiferromagnetic interactions are present in these tilted compounds at high temperatures, the strength of the exchange interaction is greater in α-BaVF5 due to the high Curie−Weiss temperature of θCW = -66.0(1)K. Furthermore, magnetic measurements revealed that α-BaVF5 exhibits a canted antiferromagnetic ground state, while BaV(F,OH)5 displays antiferromagnetic behaviour at low temperatures.

Novel B6P6X (X=As, Sb) monolayers for antiferromagnetic spintronics and hydrogen storage

Embedding foreign atoms into porous two-dimensional (2D) materials has emerged as a promising strategy to tailor their electronic, magnetic, and adsorption properties, enabling promising applications in energy storage and spintronics devices. In this work, spin-polarized density functional theory (DFT) calculations were employed to investigate the ground state properties and hydrogen (H2) storage of interstitially X = As and Sb atom doped B6P6 (B6P6X) graphenylene monolayers. The resulting B6P6X (X = As, Sb) monolayers exhibit very good mechanical, dynamical, and thermal stabilities with antiferromagnetic (AFM) ground states. Electronic structure calculations reveal AFM semiconducting behavior for both monolayers, with indirect/direct band gaps of 0.71/0.60 eV (PBE) and 2.19/2.14 eV (HSE06) for B6P6As/B6P6Sb, respectively. All B6P6X monolayers exhibit an in-plane easy magnetization axis. The obtained Berezinskii-Kosterlitz–Thouless transition (BKT) temperature value of B6P6Sb monolayer is 268.74 K. Furthermore, the H2 storage capabilities of these B6P6X monolayers were examined. We find that B6P6As and B6P6Sb monolayers can each adsorb up to 48H2 molecules with an average adsorption energy (Ea) of -0.14 eV/H2. The corresponding H2 storage gravimetric capacities are 6.91 wt% for B6P6As@48H2 and 6.10 wt% for B6P6As@48H2, surpassing the U.S. Department of Energy’s 2025 target of 5.50 wt%. These findings highlighting the potential of B6P6X (X = As, Sb) monolayers for AFM spintronics and H2 storage applications.

Strain induced magnetic switching in ferrimagnetic Mn2Ge: A first principles study

This study employs first-principles calculations to investigate the electronic and magnetic properties of Ni2In type Mn2Ge. Our total energy calculations suggests that ferrimagnetic state is more probable compared to the ferromagnetic state as the ground state for hexagonal Mn2Ge. The applied lattice strain is found to have influence in flipping the spins of Mn atoms from a ferromagnetic state to an antiferromagnetic state. An analysis of the electronic band structure reveals the metallic nature in Mn2Ge. However, the existence of Weyl points and Dirac nodal lines introduces an additional layer of complexity, positioning hexagonal Mn2Ge as an attractive topological ferrimagnetic material with unique magnetostrictive properties. These insights might pave the way for further investigation and potential applications in the realm of spin-based technologies.

Study of Structural, Magnetic, and Thermoelectric Properties of Rare Earth-based CdCe2X4 (X = S, Se, Te) Spinels for Spintronic and Energy Harvesting Applications

Controlling the spin degree of freedom in electronics paves the way for novel approaches to employ, relocate, and store data at accelerated rates. In this regard, an in-depth examination of the structural, electronic, magnetic, and transport behaviour of CdCe2X4 (X = S, Se, Te) is undertaken. It is observed that ferromagnetic states exhibit higher energy release compared to antiferromagnetic states. Room temperature ferromagnetism is characterized by the Tc and spin-polarized density of states. The underlying mechanism in ferromagnetic behaviour is elicited in terms of crystal field energy, double exchange mechanism, exchange energies, and constants. The magnetic moment shift from Ce to other NM sites (Cd, X) is identified as a mechanism sustaining ferromagnetic character through electron exchange, thereby preventing clustering. Furthermore, the temperature-dependent thermoelectric properties are investigated, encompassing electrical and thermal conductivity, Seebeck coefficient, and power factor, recommending exploration of spinels as potential candidates for sustainable energy devices.

Theoretical Study on BiCoO3: Pressure‐Tuned Transformation of Structure, Magnetism, Charge, and Spin State

AbstractThe atomic structures, electronic structures, magnetic properties, and spin states of BiCoO3 multiferroic material under hydrostatic pressure are comprehensively investigated by using first‐principles calculation based on density functional theory. Firstly, we found the pressure‐tuned structural symmetry transition from tetragonal P4 mm (No. 99) to cubic Pmm (No. 221) space group. The structural transformation prompts the Co─O polyhedral coordination transfer from a CoO5 pyramidal to a CoO6 distorted octahedron. Secondly, the pressure‐induced magnetic change from C‐type antiferromagnetic state to ferromagnetic state and then to paramagnetic configuration occurred after continuous compression of the volume. Essentially, the fundamental reason for the transition of the magnetic structure lies in the change of the internal atomic structure, such as the pressure induced abrupt changes of Co─O bond length and <Co─O─Co> bond angle. Meanwhile, an obvious volume collapse was observed when the pressure was applied to 51–56 GPa. Finally, as the pressure increases, the magnetism changes from C‐type antiferromagnetic state to paramagnetic configuration, accompanying the transformation from high spin state with b2g2eg2a1g1b1g1 configuration in pyramid structure to low spin state with t2g6eg0 in octahedral field. Therefore, our results demonstrate that applied hydrostatic pressure in BiCoO3 can trigger the transformation of structure, magnetism, charge, and spin state.

Giant piezoelectricity in antiferromagnetic CrS2 and CrSe2 monolayers

Abstract Two-dimensional (2D) materials, particularly transition metal dichalcogenides (TMDs), have garnered significant attention in the nanoscale piezoelectric field due to their high crystallinity and ability to withstand large strains. Through density-functional theory calculations, we have discovered that monolayer H-phase CrS2 and CrSe2 exhibit antiferromagnetic semiconducting properties, in contrast to the previously held belief that they were nonmagnetic (NM) semiconductors. While the piezoelectric coefficients of NM CrS2 and CrSe2 are comparable to those of MoS2, their antiferromagnetic ground states demonstrate significantly enhanced piezoelectric coefficients ( d 11 ) of 27.66 pm V−1 and 52.36 pm V−1, respectively. These values exceed that of MoS2 by an order of magnitude, marking the highest recorded for TMD materials and the highest in 2D magnetic materials to date. The greatly enhanced piezoelectric responses in the antiferromagnetic states of CrS2 and CrSe2 compared to their NM states arise from three primary factors. Firstly, the displacement of the Wannier center under strain is more pronounced in the antiferromagnetic state, leading to a greater change in dipole moment (enhanced clamped-ion contribution). Secondly, there is a heightened polarization change due to internal atomic distortions (internal-strain term) in response to macroscopic strain in the antiferromagnetic state. Thirdly, the material undergoes a softening of the elastic coefficient in its antiferromagnetic state. These findings open new avenues for designing high-performance piezoelectric and magnetic multifunctional materials.

Collective excitations in magnetic topological insulators and axion dark matter search

We investigate collective excitations in magnetic topological insulators (TIs) and their impact on axion detection. In the three-dimensional TI model with the Hubbard term, the effective action of magnons and amplitude modes is formulated by dynamical susceptibility under the antiferromagnetic and ferromagnetic states. One of the amplitude modes is identified as “axionic” quasi-particle and its effective coupling to the electromagnetic fields turns out to be enhanced by about four orders of magnitude larger than the previous estimate, which may drastically change the sensitivity of the axion search using “axion” in magnetic TIs.

Half-Metal Ferromagnetism V-Doped GaN Nanosheet Application in Spintronic Device

The density functional theory calculations using general gradient approximation (GGA) have been systematically performed to study the electronic structures, the density of states (DOS), and magnetic properties of V-doped GaN nanosheet for different dopant concentrations (2.08% and 4.16%). We conducted the entire study using the Atomistixtool kit code. The electronic properties were improved with the Hubbard values U = 4 eV. V-doped CaN nanosheet exhibits stable ferromagnetic (FM) states relative to corresponding antiferromagnetic (AFM) states. The calculated TC with the V-doping is found to be above the room temperature (RT) one. Calculation results reveal that V-doped nanosheets may be a good candidates for spintronics due to its good half-metal ferromagnetism.

The mysterious magnetic ground state of Ba14MnBi11 is likely self-doped and altermagnetic

Magnetism in the Zintl compound Ba14MnBi11 is rather poorly understood. Experimental claims are largely inconsistent with ab initio calculations, much beyond typical errors of the latter. We revisit this old problem, assuming that the root of the problem may be in nonstoichiometry of existing samples. Our key finding is that the magnetic ground state is indeed very susceptible to charge doping (band filling). Calculations for stoichiometric Ba14MnBi11 give a rather stable ferromagnetic metallic state, in agreement with previous publications. However, by adding exactly one electron per Mn, the system becomes semiconducting as expected, and becomes weakly antiferromagnetic (AF). On the other hand, upon small amount of hole doping, the system transitions to a special type of AF state known as altermagnetism. Furthermore, hole and electron doping-induced phase transitions result from different underlying mechanisms, influencing different exchange pathways. We propose that the inconsistency between experiment and theory is not a failure of the latter, but results from a nontrivial ramification of nonstoichiometry. The possibility of doping-stabilized altermagnetism is exciting.

Thin film synthesis, structural analysis, and magnetic properties of novel ternary transition metal nitride MnCoN2

Recent high-throughput computational searches have predicted many novel ternary nitride compounds providing new opportunities for materials discovery in underexplored phase spaces. Nevertheless, there are hardly any predictions and/or syntheses that incorporate only transition metals into new ternary nitrides. Here, we report on the synthesis, structure, and properties of MnCoN2, a new ternary nitride material comprising only transition metals and N. We find that crystalline MnCoN2 can be stabilized over its competing binaries, and over a tendency of this system to become amorphous, by controlling growth temperature within a narrow window slightly above ambient condition. We find that single-phase MnCoN2 thin films form in a cation-disordered rocksalt crystal structure. X-ray photoelectron spectroscopy analysis suggests that MnCoN2 is sensitive to oxygen through various oxides and hydroxides binding to cobalt on the surface. X-ray absorption spectroscopy is used to verify that Mn3+ and Co3+ cations exist in an octahedrally coordinated environment, which is distinct from a combination of CoN and MnN binaries and in agreement with the rocksalt-based crystal structure prediction. Magnetic measurements suggest that MnCoN2 has a canted antiferromagnetic ground state below 10 K. We extract a Weiss temperature of θ=−49.7K, highlighting the antiferromagnetic correlations in MnCoN2. Published by the American Physical Society 2024

First−Principle Study on Electronic Structure and Magnetism in Doped Boron Phosphide Nanosheet

Based on the first‐principles calculation of density‐functional theory, the electronic structure and magnetic properties of hexagonal boron phosphide (h‐BP) with doping and applying strain to the transition‐metal (TM = Cr, Mn, Fe, Co, and Ni) elements are investigated. After the TM elements are introduced, the magnetism is induced. The magnetic moments are 3.00, 3.87, 1.00, 1.99, and 1.00 μB, respectively, which mainly contributed by the 3d orbitals of TM elements. In the case of magnetic coupling, Cr–Cr are mainly coupled antiferromagnetically at different distances. In addition, Fe–Fe performs a ferromagnetic state, and Co–Co represents an antiferromagnetic state with the distance of 3.213 Å. After applied strain, Co doped of the system shows the characteristics of semimetals under the application of 4% strain. It can be added that for h‐BP systems, doping Co and Mn increases its conductivity, which is beneficial to the study of spintronic materials.

Surface weak ferromagnet coupling induced giant room-temperature spontaneous exchange bias in antiferromagnet Fe3BO6 polycrystals.

The spontaneous exchange bias effect (SEB) has wide application prospects in information storage technologies. In this study, nanoscale raw materials were used to fabricate antiferromagnetic Fe3BO6 polycrystals. The obtained Fe3BO6 exhibited a large SEB effect, where the value of the spontaneous exchange bias field at room temperature was as large as ∼4234 Oe. The room-temperature training effect, temperature-dependence, and maximum field-dependence of the HSEB were investigated. We propose that this giant SEB originates from the exchange-coupling interactions between the weak ferromagnetic surface state and the bulk antiferromagnetic state. The theoretical analysis results were further verified by comparing the magnetic properties of the Fe3BO6 with relatively low crystallinity. The results of this investigation will help find promising candidate materials for devices based on the SEB effect.

Role of biquadratic exchange on thermodynamic quantities in anisotropic Heisenberg model

The magnetic and thermodynamic properties of the spin-1 anisotropic Heisenberg system are studied within Oguchi approximation. The system contains both the bilinear and biquadratic exchange interactions between the nearest neighboring spins located on a centered honeycomb lattice. For the positive biquadratic exchange interaction parameters, the phase transition in the Heisenberg case is of both second and first order where there is a discontinuity in the thermodynamic properties at this transition temperature. For some negative biquadratic exchange interaction parameters, in both the Heisenberg and Ising cases, the ferromagnetic state changes in favor of the antiferromagnetic state. The frustrated antiferromagnetic structure created by the biquadratic exchange parameter with negative sign was shown significantly influence the magnetization, quadrupolar moment, internal energy, heat capacity, entropy and free energy of the system, where the system has an oscillating chaotic phase regime. A double peak behavior was observed in the specific heat, with one at the critical temperature and another at a low temperature.

Prediction of multiferroicity in the layered hydrogen-bonded system α-CrOOH: Proton transfer ferroelectricity and strain-tunable magnetic transition

Ferroelectric materials with vertical polarization could provide ground-breaking device applications, compatible with electric-field switching even in the presence of a surface-depolarizing field. Herein, we present theoretical evidence that rhombohedral chromium oxide hydroxide α-CrOOH, which has been synthesized experimentally, is a type-Ⅰ multiferroic. First-principles calculations plus Monte Carlo simulations indicate that α-CrOOH is a room temperature proton transfer ferroelectricity semiconductor with robust electric polarization as large as 24.6 μC/cm2. Moreover, the system exhibits an anti-ferromagnetism ground state with a Neel temperature of 340 K, where strain can modulate the transition from antiferromagnetic to ferromagnetic. Finally, a two-dimensional (2D) heterostructure model was designed, composed of monolayer α-CrOOH and functional MXene, for various applications such as non-volatile memory (NVM). The remarkable properties may enable the system to hold great potential for the development of future multifunctional devices.

Hysteresis behavior and magnetocaloric effect in MnNiGa[formula omitted] full-Heusler alloy

In this manuscript, we studied the magnetic, magnetocaloric, and hysteresis properties of the MnNiGa2 full-Heusler alloy using mean-field theory and first-principles calculations. Initially, we employed the GGA+U method to investigate the structural characteristics of the alloy. Our findings indicated that the ferromagnetic state, with an optimal lattice parameter of 5.88 Å, was the most stable compared to the antiferromagnetic states. Additionally, the exchange interactions, defined as the Hamiltonian parameters of the studied system, were calculated and used in the mean-field approximation. The second-order transition at a Curie temperature of Tc = 373 K, previously revealed experimentally, has been confirmed. Furthermore, the alloy exhibited a relative cooling power (RCP) of 260.43 J/kg and a magnetocaloric effect of 10.34 J/kg.K at an applied magnetic field of 1.4 T. These results suggest that MnNiGa2 is a promising candidate for magnetic refrigeration applications.

Charge order near the antiferromagnetic quantum critical point in the trilayer high Tc cuprate HgBa2Ca2Cu3O8+δ

We study the transport properties of underdoped trilayer cuprate HgBa2Ca2Cu3O8+δ with doping level p = 0.10–0.12 in magnetic field up to 88 T. We report for the first time in a cuprate superconductor a dramatic change of the quantum oscillation spectrum versus temperature, which is accompanied by a sign change of the Hall effect below T ≈10 K. Based on numerical simulations, we infer a Fermi surface reconstruction in the inner plane from an antiferromagnetic state (hole pockets) to a biaxial charge density wave state (electron pockets). We show that both orders compete and share the same hotspots of the Fermi surface, and we discuss our result in the context of spin-fermion models.

Effect of edge dual-hydrogenation on electronic and magnetic properties of armchair silicon carbide nanoribbons

Using the first-principles calculations, we investigate the electronic and magnetic properties of armchair silicon carbide nanoribbon (aSiCNR) with different combinations of edge dual-hydrogenation. The dual-hydrogenation on the boundary Si or C atom changes it from sp2 hybridization to sp3 hybridization, which will have an important role on the stability of aSiCNR. Only the full dual-hydrogenation on the one edge or two edges don't change the band structure and magnetic moment of aSiCNR. However, the other different combinations of edge dual-hydrogenation can result in aSiCNR exhibiting metallic, semiconductor, and half-metallic properties under non-magnetism state, ferromagnetic and anti-ferromagnetic states. These results may present a new avenue for band engineering of aSiCNR, as well as valuable suggestions for the practical application of SiC based nanomaterials in spintronics and multifunctional nanodevices.

From Magnetostatics to Topology: Antiferromagnetic Vortex States in NiO‐Fe Nanostructures

AbstractMagnetic vortices are topological spin structures frequently found in ferromagnets, yet novel to antiferromagnets. By combining experiment and theory, it is demonstrated that in a nanostructured antiferromagnetic‐ferromagnetic NiO(111)‐Fe(110) bilayer, a magnetic vortex is naturally stabilized by magnetostatic interactions in the ferromagnet and is imprinted onto the adjacent antiferromagnet via interface exchange coupling. Micromagnetic simulations are used to construct a corresponding phase diagram of the stability of the imprinted antiferromagnetic vortex state. The in‐depth analysis reveals that the interplay between interface exchange coupling and the antiferromagnet magnetic anisotropy plays a crucial role in locally reorienting the Néel vector out‐of‐plane in the prototypical in‐plane antiferromagnet NiO and thereby stabilizing the vortices in the antiferromagnet.