Antiferromagnetic Research Articles

Unconventional Magnetic and Magneto-Transport Properties in Quasi-2D Ni0.28TaSeS Single Crystal.

Van der Waals (vdW) magnetic materials have broad application prospects in next-generation spintronics. Inserting magnetic elements into nonmagnetic vdWmaterials can introduce magnetism and enhance various transport properties. Herein, the unconventional magnetic and magneto-transport phenomena is reported in Ni0.28TaSeS crystal by intercalating Ni atoms into nonmagnetic 2H-TaSeS matrix. Magnetic characterization reveals a canted magnetic structure in Ni0.28TaSeS, which results in an antiferromagnetic (AFM) order along the c-axis and a ferromagnetic (FM) moment in the ab-plane. The presence of spin-flop (SF) behavior can also be attributed to the canted magnetic structure. Temperature-dependent resistivity exhibits a metallic behavior with an abrupt decrease corresponding to the magnetic transition. Magneto-transport measurements demonstrate a positive magnetoresistance (MR) with a plateau that is different from conventional magnetic materials. The field-dependent Hall signal exhibits nonlinear field dependence when the material is in magnetically ordered state. These unconventional magneto-transport behaviors are attributed to the field-induced formation of a complex spin texture in Ni0.28TaSeS. In addition, it further investigated the angle dependence of MR and observed an unusual fourfold anisotropic magnetoresistance (AMR) effect. This work inspires future research on spintronic devices utilizing magnetic atom-intercalated quasi-2D materials.

A Brilliant Magnetic Refrigerant Operating Near Liquid Helium Temperature: Enhanced Magnetocaloric Effect in Ferromagnetic EuTi0.75Al0.125Zr0.125O3

AbstractRare earth‐based perovskites have become an attractive research interest in the field of cryogenic magnetic refrigerants due to their unique advantages in practical applications. The remarkable magnetocaloric effect (MCE) renders EuTiO3 a potential magnetic refrigerant in the liquid helium temperature range. More impressively, the tunability between antiferromagnetism (AFM) and ferromagnetism (FM) provides the feasibility of tailoring the magnetism and enhancing the magnetocaloric performance. In this study, the magnetism of EuTi0.75Al0.125Zr0.125O3 is investigated in depth through first‐principles calculations and experimental methods. Both theoretical calculations and experimental results reveal that it exhibits significant ferromagnetism due to the AFM‐FM magnetic transition promoted by the co‐substitution of Al and Zr. Lattice expansion and altered electronic interactions are responsible for the FM behavior, which leads to a significant enhancement of the MCE. With the field change of 0−1 T, the peak values of magnetic entropy change (−ΔSM), refrigerating capacity (RC), and adiabatic temperature change (ΔTad) reach 18.9 J kg−1 K−1, 77.7 J kg−1, and 7.4 K, respectively. More surprisingly, the values of maximum magnetic entropy change () and maximum adiabatic temperature change for EuTi0.75Al0.125Zr0.125O3 reach 11.4 J kg−1 K−1 and 3.7 K under the field change of 0−0.5 T, respectively. The remarkable magnetocaloric performance proves it to be a brilliant magnetic refrigerant operating near liquid helium temperature.

Bath-Engineering Magnetic Order in Quantum Spin Chains: An Analytic Mapping Approach.

Dissipative processes can drive different magnetic orders in quantum spin chains. Using a nonperturbative analytic mapping framework, we systematically show how to structure different magnetic orders in spin systems by controlling the locality of the attached baths. Our mapping approach reveals analytically the impact of spin-bath couplings, leading to the suppression of spin splittings, bath dressing and mixing of spin-spin interactions, and emergence of nonlocal ferromagnetic interactions between spins coupled to the same bath, which become long ranged for a global bath. Our general mapping method can be readily applied to a variety of spin models: we demonstrate (i)a bath-induced transition from antiferromagnetic (AFM) to ferromagnetic ordering in a Heisenberg spin chain, (ii)AFM to extended Neel phase ordering within a transverse-field Ising chain with pairwise couplings to baths, and (iii)a quantum phase transition in the fully connected Ising model. Our method is nonperturbative in the system-bath coupling. It holds for a variety of non-Markovian baths and it can be readily applied towards studying bath-engineered phases in frustrated or topological materials.

Investigation of the structural and magnetic properties of the GdCoC compound featuring excellent cryogenic magnetocaloric performance

Magnetic refrigeration (MR) based on the magnetocaloric effect (MCE) has been recognized as an environmentally benign and energy-efficient cooling technology. Exploring suitable magnetocaloric materials is a crucial prerequisite for practical MR applications. We have herein provided a systematic investigation of the crystal structure, microstructure, electronic structure, magnetic phase transition, critical behavior, and MCE of the GdCoC compound featuring excellent cryogenic magnetocaloric performance by means of experimental determination and theoretical calculation. The GdCoC compound is crystallized in a simple layered tetragonal crystal structure with a P42/mmc space group and undergoes two successive ferromagnetic (FM) transitions along with a low-temperature weak antiferromagnetic (AFM) transition under low magnetic fields. Density functional theory calculations confirms the FM coupling of the Gd and Co intra-sublattice interactions, whereas AFM coupling for their inter-sublattice interaction. The magnetic transitions are merged in to one under high magnetic fields which has been confirmed to be second-order type and its critical behavior can be understood in the framework of tri-critical mean-field model, whereas the low-temperature weak AFM transition is belonging to the first-order type. The excellent magnetocaloric performance of the GdCoC compound was identified by the parameters of magnetic entropy change, adiabatic temperature change, temperature-averaged entropy change, relative cooling power, and refrigerant capacity, which are superior to most of the well-known magnetocaloric materials with similar working temperatures, making it attractive for practical cryogenic MR applications.

Magneto-transport and thermoelectric studies of antiperovskite semimetal: Mn3SnC

We explore the magnetotransport and thermoelectric (Seebeck and Nernst coefficients) properties of Mn3SnC, an antiperovskite magnetic Nodal line semimetal. Mn3SnC shows paramagnetic (PM) to concurrent antiferromagnetic (AFM)/ferromagnetic (FM) transition at T ∼ 286 K. The electrical resistivity and Seebeck coefficient indicate the importance of electron–magnon scattering in the concurrent AFM/FM regime. We observed a large positive magnetoresistance (MR) of ∼8.2 at 8 T field near magnetic transition, in the otherwise negative MR behaviour for low temperatures. The electrical resistivity and MR show a weak thermal hysteresis around the boundary of transition temperature and the width of hysteresis decreases as magnetic field increases. Interestingly the Hall and Seebeck coefficients change sign from positive to negative below the transition temperature, highlighting the different scattering for holes and electrons in this multi-band system. The Seebeck and Nernst signal exhibit two sharp anomalies; one at the transition temperature and another at ∼50 K. The anomaly at magnetic transition in the Nernst signal disappear at 8 T magnetic field, owing to the reduction of magnetic fluctuation. A pseudo-gap near the Fermi level produces an upturn with a broad minimum in the Seebeck signal.

Hydrogen-annealing modulated magnetocaloric effect and critical behavior of Weyl semimetallic Co3Sn2S2

Modulating the electron interaction and magnetic domains is an essential strategy to evoke novel physical properties, both for fundamental research and for related magnetic applications. The emerging annealing process attracted attention due to its capability of tuning the magnetic performance, but it has been rarely studied. Herein, we conducted hydrogen annealing on the Weyl semimetallic Co3Sn2S2 and investigated the magnetic interaction, critical behavior, and magnetocaloric effect (MCE). Hydrogen-annealed Co3Sn2S2 (HA-Co3Sn2S2) exhibits a distinct anisotropy-dependent magnetic behavior, where a typical second-order transition with an easy magnetization process is observed under H//c. However, a frustrated magnetic state composed of ferromagnetic (FM), antiferromagnetic (AFM), and/or spin glass phases is observed when H//ab. Critical analyses illustrate that the ground state of HA-Co3Sn2S2 lies between the 3D-Ising model and the Mean-filed model, indicating the presence of both long-range and short-range magnetic interactions in the system. Additionally, we found that HA-Co3Sn2S2 exhibits an enhanced saturation magnetization (Ms) and magnetic refrigeration capacity, both showing anisotropic dependence, compared to the pristine Co3Sn2S2. Our work develops hydrogen annealing to modulate electron coupling and magnetic domains, paving the way for further studies of anisotropic magnetic behavior and applications in magnetic refrigeration.

Unveiling chiral states in the XXZ chain: finite-size scaling probing symmetry-enriched c = 1 conformal field theories

We study the low-energy properties of the one-dimensional spin-1/2 XXZ chain with time-reversal symmetry-breaking pseudo-scalar chiral interaction and propose a phase diagram for the model. In the integrable case of the isotropic Heisenberg model with the chiral interaction, we employ the thermodynamic Bethe ansatz to find “chiralization”, the response of the ground state versus the strength of the pseudo-scalar chiral interaction of a chiral Heisenberg chain. Unlike the magnetization case, the chirality of the ground state remains zero until the transition point corresponding to critical coupling αc = 2J/π with J being the antiferromagnetic spin-exchange interaction. The central-charge c = 1 conformal field theories (CFTs) describe the two phases with zero and finite chirality. We show for this particular case and conjecture more generally for similar phase transitions that the difference between two emergent CFTs with identical central charges lies in the symmetry of their ground state (lightest weight) primary fields, i.e., the two phases are symmetry-enriched CFTs. At finite but small temperatures, the non-chiral Heisenberg phase acquires a finite chirality that scales with the temperature quadratically. We show that the finite-size effect around the transition point probes the transition.

Annealing-Tunable Charge Density Wave in the Magnetic Kagome Material FeGe.

The unprecedented phenomenon that a charge density wave (CDW) emerges inside the antiferromagnetic (AFM) phase indicates an unusual CDW mechanism associated with magnetism in FeGe. Here, we demonstrate that both the CDW and magnetism of FeGe can be effectively tuned through postgrowth annealing treatments. Instead of the short-range CDW reported earlier, a long-range CDW order is realized below 110K in single crystals annealed at 320 °C for over 48h. The CDW and AFM transition temperatures appear to be inversely correlated with each other. The onset of the CDW phase significantly reduces the critical field of the spin-flop transition, whereas the CDW transition remains stable against minor variations in magnetic orders such as annealing-induced magnetic clusters and spin-canting transitions. Single-crystal x-ray diffraction measurements reveal substantial disorder on the Ge1 site, which is characterized by displacement of the Ge1 atom from the Fe_{3}Ge layer along the c axis and can be reversibly modified by the annealing process. The observed annealing-tunable CDW and magnetic orders can be well understood in terms of disorder on the Ge1 site. Our study provides a vital starting point for the exploration of the unconventional CDW mechanism in FeGe and of kagome materials in general.

Observation of Magnetic Field‐Induced and Partially Switchable Electric Polarization in Spin‐Chain FePbBiO4

AbstractThe linear magnetoelectric (ME) characteristics of a quasi‐1D spin‐chain compound, FePbBiO4, are reported. Two distinct antiferromagnetic (AFM) orders occurring at ≈23 K (TN1) and 12 K (TN2) are verified using magnetization, specific heat, and conspicuous dielectric (ε′) anomalies. A striking observation is that no pyrocurrent (Ipy) is detected in the absence of magnetic field (H); however, H‐induced ferroelectric polarization (P) at TN1 and P unexpectedly partially switches or reverses below TN2 as reproduced by applying positive and negative electric fields (E). The resulting magnetic field and temperature (H‐T) phase diagram illustrates T‐dependent H‐induced spin reorientation and electric P. The interaction between T, H, spin dynamics, and lattice structures is pivotal and is qualitatively discussed and proposed as an explanation for the observed ME nature.

Triindenotriphenylenes: Spin-Frustrated Triskelion Triradicals with Excellent Ambient Stability.

A triskelion-shaped triradical triindeno[1,2-a:1',2'-g : 1'',2''-m]triphenylen-7-yl (1) and its internally fused derivative (2) obtained by oxidative cyclization were prepared in a straightforward synthetic sequence. Both compounds were confirmed to be triradicals and to possess intramolecular antiferromagnetic exchange interactions between spins, displaying a spin-frustrated doublet ground state with doublet-quartet energy gaps of -0.14 kcal/mol for 1 and -0.06 kcal/mol for 2. Despite their open-shell character, they were sufficiently stable to be handled under ambient conditions on a timescale of days. Both compounds could be reversibly reduced to mono-, di-, and trianions and oxidized to 1+ and 22+, with strong NIR absorptions (1800 to over 3200 nm) observed for all open-shell ions.

Triindenotriphenylenes: Spin‐Frustrated Triskelion Triradicals with Excellent Ambient Stability

A triskelion‐shaped triradical triindeno[1,2‐a:1',2'‐g:1'',2''‐m]triphenylen‐7‐yl (1) and its internally fused derivative obtained by oxidative cyclization (2) were prepared in a straightforward synthetic sequence. Both compounds were confirmed to be triradicals and to possess intramolecular antiferromagnetic exchange interactions between spins, displaying a spin‐frustrated doublet ground state with doublet‐quartet energy gaps of −0.14 kcal/mol for 1 and −0.06 kcal/mol for 2. Despite their open‐shell character, they were sufficiently stable to be handled under ambient conditions on a timescale of days. Both compounds could be reversibly reduced to mono‐, di‐, and trianions and oxidized to 1+ and 22+, with strong NIR absorptions (1800 to over 3200 nm) observed for all open‐shell ions.

Magnetic properties of Dy[formula omitted](Co,Ni) compounds at ambient and high pressures

Dy3Co, in addition to two antiferromagnetic (AFM) transitions (35 K and TN∼ 44 K), exhibits a Griffiths-like phase around 65 K and it persists up to ∼1 GPa pressure. External pressure alters the magnetic state significantly and results in increase (decrease) of TN (TAF) by 6.5% (∼13%) with dTN/dP ∼ 3 K/GPa (dTAF/dP ∼ −4.5 K/GPa). Increase in metamagnetic critical field and other changes with pressure indicate the strengthening of AFM interactions in Dy3Co. On the other hand, Dy3Ni shows three magnetic transitions at To∼ 55 K, T1∼ 39 K (AFM) and T2∼ 24 K (AFM). Experimental evidence points to the magnetic ordering temperature to be at To∼55 K instead of 39 K as claimed by certain reports. External pressure reduces (increases) the transition temperature To (T1) by ∼7.9% (7.6%) at a rate of −3.5 K/GPa (2.5 K/GPa). Pressure has only marginal effect on the other low temperature transition at T2. Additionally, ac-susceptibility data exhibit spin-glass like features, which seem to arise from domain wall movements and probably random freezing of small components of spins, coexisting with dominant long-ranged non-collinear AFM structure in these compounds.

Synthesis, characterization and study of magnetic property of two isomorphic Cu(II) coordination polymers (CP) with chromone based ligand systems

Synthesis, characterization and magnetic properties of two Cu(II)-based coordination polymers (CPs, [{Cu(L1)(N(CN)2)}(ClO4)]n L1 = 3-(((2-(diethylamino)ethyl)imino)methyl)-4H-chromen-4-one (1) and [{Cu(L2)(N(CN)2)}(ClO4)]n L2 = 3-(((2-(dimethylamino)ethyl)imino)methyl)-4H-chromen-4-one (2)) involving chromone based chelating ligands and dicyanamide bridging ligands are reported. Both compounds have been characterized by physicochemical methods and the crystal structures have been determined by X-ray diffraction analysis, disclosing that they are isostructural and isomorphous compounds of polymeric linear chains where the central metal has adopted distorted square pyramidal coordination geometry. The magnetic studies reveal that the synthesized compounds show a prevailing paramagnetic behavior. Only below 15 K does a weak antiferromagnetic interaction become effective in these systems, and they have been further analyzed and interpreted.

Neuromorphic Computing with Emerging Antiferromagnetic Ordering in Spin-Orbit Torque Devices.

Field-free switching (FFS) and spin-orbit torque (SOT)-based neuromorphic characteristics were realized in a W/Pt/Co/NiO/Pt heterostructure with a perpendicular exchange bias (HEB) for brain-inspired neuromorphic computing (NC). Experimental results using NiO-based SOT devices guided the development of fully spin-based artificial synapses and sigmoidal neurons for implementation in a three-layer artificial neural network. This system achieved impressive accuracies of 91-96% when applied to the Modified National Institute of Standards and Technology (MNIST) image data set and 78.85-81.25% when applied to Fashion MNIST images, due presumably to the emergence of robust NiO antiferromagnetic (AFM) ordering. The emergence of AFM ordering favored the FFS with an enhanced HEB, which suppressed the memristivity and reduced the recognition accuracy. This indicates a trade-off between the requirements for solid-state memory and those required for brain-inspired NC devices. Nonetheless, our findings revealed opportunities by which the two technologies could be aligned via controllable exchange coupling.

Modeling the manganese deposit on the BP (111)-(2×2) surface: Density functional theory studies

The structural, electronic, and magnetic properties of the manganese (Mn) adsorption and incorporation into the boron phosphide (BP) in surface (111) – periodicity (2 × 2) structure have been investigated using spin-polarized first-principles total-energy calculations. The exchange-correlation energies are treated within the generalized gradient approximation. The magnetic properties have been studied by considering different coverages and magnetic configurations. The Mn adsorption and incorporation range from ¼ to 1 monolayer (ML), with results displaying: Ferromagnetic (FM), antiferromagnetic (AFM), and non-magnetic (NM) behavior at low, intermediate, and high coverages, respectively. The electronic properties are explored considering the total density of states (DOS) and the projected density of states (PDOS). It is noted that the contribution of the Mn-d orbital modifies the metallicity of the surface. The results show that the most favorable structure is the 1 Mn ML adsorption, with an AFM alignment and a magnetic moment of 0 μB/atom. The material exhibits metallicity at the first monolayer induced by manganese, while the lower internal layers are semiconductors. Finally, the charge density distribution corroborates the surface metallic phase, which indicates that the proposed material can be helpful in the design of new spintronic devices.

Hourglass-Shaped Homo- and Heteronuclear Nonanuclear Lanthanide Clusters: Structures, Magnetism, Photoluminescence, and Theoretical Analysis.

Synthesis of nonameric cationic clusters [Dy9(acac)16(μ3-OH)8(μ4-OH)2]OH·6H2O (1), [Dy8Tb (acac)16(μ3-OH)8(μ4-OH)2]OH·2H2O (2), and [Gd9(acac)16(μ3-OH)8(μ4-OH)2]OH·6H2O (3) (acac = acetylacetonate) is reported. The emission spectrum of 1 shows Dy(III) ion characteristic bands assignable to the 4F9/2 → 6HJ (J = 15/2 to 9/2) transitions. Emission due to both Dy(III) and Tb(III) ions is observed for 2 in the visible range, with Tb(III) specific bands appearing due to the 5D4 → 7FJ (J = 6, 4, and 3) transitions. Cluster 3 exhibits a significant magnetocaloric effect (MCE), with -ΔSm values increasing with decrease in temperature and increase in field, reaching -ΔSmmax = 20.98 J kg-1 K-1 at 2 K and 9 T. Isotropic magnetic coupling constants (Js) in 3 derived from density functional theory (DFT) calculations reveal that the exchange interactions are antiferromagnetic and weak. Compound 3 possesses S = 7/2 ground state arising from the central Gd(III) ion along with several nested excited states due to competing antiferromagnetic interactions that yield reasonably large MCE values. Utilizing computed exchange coupling interactions, we have performed ab initio CASSCF/RASSI-SO/POL_ANISO calculations on antiferromagnetic 1 and 2 to estimate the exchange interactions using the Lines model. For 2, Dy(III)···Tb(III) exchange interactions were extracted for the first time and were found to be weakly antiferromagnetically coupled.

Interpenetrated Lattices of Quaternary Chalcogenides Displaying Magnetic Frustration, High Na-Ion Conductivity, and Cation Redox in Na-Ion Batteries.

A series of quaternary selenides, NaxMGaSe4 (M = Mn, Fe, and mixed Zn/Fe), have been synthesized for the first time employing a high-temperature solid-state synthesis route through stochiometric or polychalcogenide flux reactions. Along with the selenides, a previously reported sulfide analogue, NaxFeGaS4, is also revisited with new findings. These compounds form an interpenetrated structure made up of a supertetrahedral unit. The electrochemical evaluations exhibit a reversible (de)intercalation of ∼0.6 and ∼0.45 Na-ions, respectively, from Na2.87FeGaS4 (1a) and Na2.5FeGaSe4 (2) involving Fe2+/Fe3+ redox when cycled between 1.5 and 2.5 V. Mössbauer spectroscopy of 1a shows the existence of a mixed oxidation state of Fe2+/3+ in the pristine compound and reversible oxidation of Fe2+ to Fe3+ during the electrochemical cycles. Na2.79Zn0.6Fe0.4GaSe4 possesses a reasonably high room temperature ionic conductivity of 0.077 ms/cm with an activation energy of 0.30 eV. The preliminary magnetic measurements show a bifurcation of FC-ZFC at 4.5 and 2.5 K, respectively, for 1a and Na3MnGaSe4 (4) arising most likely from a spin-glass like transition. The high negative values of the Weiss constants -368.15 and -308.43 K for 1a and 4, respectively, indicate strong antiferromagnetic interactions between the magnetic ions and also emphasize the presence of a high degree of magnetic frustration in these compounds.

Ba4RuMn2O10: A Noncentrosymmetric Polar Crystal Structure with Disordered Trimers.

Phase-pure polycrystalline Ba4RuMn2O10 was prepared and determined to adopt the noncentrosymmetric polar crystal structure (space group Cmc21) based on results of second harmonic generation, convergent beam electron diffraction, and Rietveld refinements using powder neutron diffraction data. The crystal structure features zigzag chains of corner-shared trimers, which contain three distorted face-sharing octahedra. The three metal sites in the trimers are occupied by disordered Ru/Mn with three different ratios: Ru1:Mn1 = 0.202(8):0.798(8), Ru2:Mn2 = 0.27(1):0.73(1), and Ru3:Mn3 = 0.40(1):0.60(1), successfully lowering the symmetry and inducing the polar crystal structure from the centrosymmetric parent compounds Ba4T3O10 (T = Mn, Ru; space group Cmca). The valence state of Ru/Mn is confirmed to be +4 according to X-ray absorption near-edge spectroscopy. Ba4RuMn2O10 is a narrow bandgap (∼0.6 eV) semiconductor exhibiting spin-glass behavior with strong magnetic frustration and antiferromagnetic interactions.

Macroscopic tunneling probe of Moiré spin textures in twisted CrI3

Various noncollinear spin textures and magnetic phases have been predicted in twisted two-dimensional CrI3 due to competing ferromagnetic (FM) and antiferromagnetic (AFM) interlayer exchange from moiré stacking—with potential spintronic applications even when the underlying material possesses a negligible Dzyaloshinskii–Moriya or dipole–dipole interaction. Recent measurements have shown evidence of coexisting FM and AFM layer order in small-twist-angle CrI3 bilayers and double bilayers. Yet, the nature of the magnetic textures remains unresolved and possibilities for their manipulation and electrical readout are unexplored. Here, we use tunneling magnetoresistance to investigate the collective spin states of twisted double-bilayer CrI3 under both out-of-plane and in-plane magnetic fields together with detailed micromagnetic simulations of domain dynamics based on magnetic circular dichroism. Our results capture hysteretic and anisotropic field evolutions of the magnetic states and we further uncover two distinct non-volatile spin textures (out-of-plane and in-plane domains) at ≈1° twist angle, with a different global tunneling resistance that can be switched by magnetic field.

Current-driven fast magnetic octupole domain-wall motion in noncollinear antiferromagnets

Antiferromagnets (AFMs) have the natural advantages of terahertz spin dynamics and negligible stray fields, thus appealing for use in domain-wall applications. However, their insensitive magneto-electric responses make controlling them in domain-wall devices challenging. Recent research on noncollinear chiral AFMs Mn3X (X = Sn, Ge) enabled us to detect and manipulate their magnetic octupole domain states. Here, we demonstrate a current-driven fast magnetic octupole domain-wall (MODW) motion in Mn3X. The magneto-optical Kerr observation reveals the Néel-like MODW of Mn3Ge can be accelerated up to 750 m s-1 with a current density of only 7.56 × 1010 A m-2 without external magnetic fields. The MODWs show extremely high mobility with a small critical current density. We theoretically extend the spin-torque phenomenology for domain-wall dynamics from collinear to noncollinear magnetic systems. Our study opens a new route for antiferromagnetic domain-wall-based applications.