Antiferromagnetic Coupling Interactions Research Articles

Coexistence of antiferromagnetism and unconventional superconductivity in a quasi-one-dimensional flat-band system: Creutz lattice

We study the coexistence of antiferromagnetism and unconventional superconductivity on the Creutz lattice which shows strictly flat bands in the noninteracting regime. The famous renormalized mean-field theory is used to deal with strong electron–electron repulsive Hubbard interaction in the effective low-energy t–J model, the superfluid weight of the unconventional superconducting state has been calculated via the linear response theory. An unconventional superconducting state with both spin-singlet and staggered spin-triplet pairs emerges beyond a critical antiferromagnetic coupling interaction, while antiferromagnetism accompanies this state. The superconducting state with only spin-singlet pairs is dominant with paramagnetic phase. The A phase is analogous to the pseudogap phase, which shows that electrons go to form pairs but do not cause a supercurrent. We also show the superfluid behavior of the unconventional superconducting state and its critical temperature. It is proven directly that the flat band can effectively raise the critical temperature of superconductivity. It is implementable to simulate and control strongly-correlated electrons’ behavior on the Creutz lattice in the ultracold atoms experiment or other artificial structures. Our results may help the understanding of the interplay between unconventional superconductivity and magnetism.

Topological Hall Effect in (Mn1−xFex)3.25Ge (x = 0.4) Hexagonal Magnet

Topologically protected nontrivial spin structures attract significant interest in condensed matter physics for their utilization in low‐power‐consumption spintronics devices, memory devices, etc. The topological Hall effect (THE) is an additional Hall resistivity in the system arising from real‐space Berry curvature picked up by conduction electron passing through the nontrivial spin texture. Compared to expensive neutron diffraction measurements, THE is often used as a cost‐effective tool to investigate nontrivial spin texture in the materials. In the present manuscript, THE in the (Mn1−xFex)3.25Ge (x = 0.4) alloy is studied using magneto‐transport measurements. Maximum THE is found in the system about 0.65 μΩ cm at 150 K, which is in contrast to the pristine Mn3Ge that has zero THE. The strong temperature variation of THE suggests that the noncoplanar spin structure due to competition among the magneto‐crystalline anisotropy, antiferromagnetic coupling, and ferromagnetic exchange interaction is the main source of THE in the present system. Herein, it is shown that chemical doping can be an effective way to induce THE in the material with vanishing THE in its parent phase.

Investigations on low temperature magnetic and magnetoelectric properties of multiferroic-NiO nanocomposites

Multiferroic BiFeO3-NiO (BFO-NiO) nanocomposites have been synthesized using sol-gel route and investigated via. the first principle DFT calculations, multiferroic-magnetoelectric response, and extremely low-temperature magnetic analysis. Powder X-ray diffraction (XRD) patterns along with Rietveld refinement data confirmed the phase purity viz. rhombohedral distorted perovskite BiFeO3- rock salt type NiO crystal structure and composite formation. Temperature dependent magnetic measurements confirmed the enhancement in the magnetism and the exchange bias effect due to the antiferromagnetic (AFM) and ferromagnetic (FM) exchange coupling interactions. Zero field cooled (ZFC) and field cooled (FC) magnetic results demonstrate the observation of typical superparamagnetic (SP) behavior for all the samples at room temperature whereas at low temperature a transition is reported from SP to quantum superparamagnetic (QSP) state through quantum tunneling of magnetic moment for all samples. Maximum polarization of 5.7μC/cm2 is observed for BFO-20% NiO composition. The noticeable change in the ferroelectric P vs E loops in the presence of external magnetic field confirm the evidence of multiferroic and magnetoelectric coupling behavior in the BFO-NiO nanocomposites. The DFT calculations have been done using WIEN2k software and found in well agreement with the reported experimental results. Further, the suitable temperature dependent magnetic squareness, evidence of considerable magnetoelectric coupling, exchange bias effect and SP nature make the BFO-NiO nanocomposites considerable suitable for various device applications such as information storage, magnetic random access memory, targeted drug delivery, magnetic resonance imaging (MRI), bio-sensing and tailoring other photocatalytic applications.

Magnetic properties of 3d metal atoms embedded in a new two-dimensional carbon sheet

A first-principles study is performed to explore the magnetic properties of the 3d transition metal (TM) atoms embedded in a new two-dimensional(2D) nonmagnetic carbon sheet. By the adsorption of 3d metal atoms (M = Sc-Ni) on the single vacancy (SV) site of 2D carbon material, the M@SV complexes are nonmagnetic for M = Ti, Co and Ni. Other metal atoms doping can induce different magnetism. The magnetic moment of Sc@SV system mainly comes from the π electrons of carbon atoms, and these electrons virtual hopping leads to the ferromagnetic coupling interaction with Sc atom. For M = V, Cr, Mn and Fe systems, the more net spin electrons go the separate nonbonding d orbitals, giving the different magnetic moments. Meanwhile, due to the Hund’s rule, the metal atoms and the surrounding carbon atoms have the anti-ferromagnetic coupling interaction. By the simple spd hybridization model, we explore the origin of the various magnetism, and provide some new magnetic single-atom materials for the future spintronics devices and spin-dependent catalysts.

Synergetic effects of combining TM single- and double-atom catalysts embedded in C2N on inducing half-metallicity: DFT study

Designing 2D-materials that exhibit half-metallic properties is crucially important in spintronic devices that are used in low-power high-density logic circuits. The large pores in the C2N morphology can stably accommodate various configurations of transition-metal (TM) atoms that can lead to ferromagnetic (FMC) and anti-ferromagnetic coupling interactions among them, and thus paving the way for achieving half-metallic characteristics. In the present study, we use manganese ‘Mn’ as a promising catalyst and the spin-polarized density-functional theory to search for suitable configurations of metal atoms that yield half-metallicity. Test samples comprised of single-atom catalyst (SAC) and double-atom catalyst (DAC) of Mn embedded in a C2N sample of size 2 × 2 primitive cells as well as their combinations in neighboring large pores (i.e. SAC–SAC, SAC–DAC, and DAC–DAC). Tests were extended to screen many other TM catalysts and the results showed the existence of half metallicity in just five cases: (a) C2N:Mn (DAC, SAC–SAC, and SAC–DAC); (b) C2N:Fe (DAC); and (c) C2N:Ni (SAC–DAC). Our results further showed the origins of half-metallicity to be attributed to FMC interactions between the catalysts with the six mirror images, formed by the periodic-boundary conditions. The FMC interaction is found to have strength of about 20 meV and critical length scale up to about ∼21–29 Å, dependent on both the type of magnetic impurity and the synergetic effects. The potential relevance of half-metallicity to spintronic device application is discussed. Our theoretical results have been benchmarked to the available data in literature and they were found to be in good agreements.

Observation of field-induced single-molecule magnet behavior in an octahedrally coordinated binuclear Co2 compound

A binuclear cobalt compound, namely, [Co2(L)2Cl2(H2O)4]·2Cl·2H2O (1), was synthesized by acylhydrazone Schiff base ligand N3-(4-pyridyl)-4-hydroxybenzoylhydrazone (HL) and CoCl2·6H2O. The crystal structure study suggests that each CoII ion in 1 is surrounded by two nitrogen atoms and one oxygen atom from ligand, one chloride ion and two oxygen atoms from two water molecules, giving rise to six-coordinated geometry, where two N atoms from two ligands as bridges link two CoII ions. The direct-current (dc) magnetic susceptibility measurements reveal the existence of antiferromagnetic coupling interaction in 1. The alternating-current (ac) magnetic susceptibility measurements indicate that 1 exhibits field-induced slow magnetic relaxation behavior with energy barrier (Ueff) of 51.80 K, standing out among Co2-SMMs. This study demonstrates that the large magnetic anisotropy of each CoII ion and the weak antiferromagnetic coupling interaction between two CoII ions can improve Co2-SMMs performance effectively.

An Unprecedented Dodecanuclear Copper(II) Complex Derived from an Unsymmetrical Schiff‐Base Ligand

AbstractA novel discrete dodecanuclear Cu(II) complex, [Cu12L26(OH)6]⋅2CH3CN (1) has been synthesised using an N2O3 donor unsymmetrical Schiff base ligand derived from the condensation of 1,3‐diamino‐2‐propanol with salicylaldehyde and o‐hydroxyacetophenone. Single crystal X‐ray diffraction study indicates that each deprotonated ligand chelates two Cu(II) centres which are also bridged by alkoxo oxygen; six such dinuclear units are joined by alkoxo and phenoxo groups of the ligand as well as hydroxo bridges to form the dodecanuclear structure. Magnetic studies indicate predominating antiferromagnetic coupling interactions between the paramagnetic Cu(II) centres.

Solvothermal synthesis, crystal structure, thermal, magnetic properties and DFT computations of a Ytterbium(III) complex derived from pyridine-2,6-dicarboxylic acid

A new ytterbium(III) complex, (DMAH2)3[Yb(Pydc)3].4H2O (1) {Pydc = Pyridine-2,6-dicarboxylate anion, DMAH2 = Dimethylammonium} has been prepared under mild solvothermal conditions and characterized by elemental analysis, IR spectroscopy, thermal analysis and single crystal X-ray diffraction. The DMAH2 molecules in 1, generated in situ from hydrolysis of N,N-dimethylformamide are responsible to assemble 2D coordination polymer through N-H···O and O-H···O hydrogen bonding. Magnetic susceptibility measurements indicate that the complex (1) obeys the Curie Weiss law and the overall magnetic behavior is typical for the presence of weak antiferromagnetic exchange coupling interactions. Theoretical data for geometrical parameters of complex 1 agree well with the experimental data. Large HOMO-LUMO energy gap of 4.33 eV has provided kinetic stability to the complex 1. NBO analysis reflects that intramolecular charge transfer occurred between ligand and metal orbitals with the highest stabilization energy of 1024.04 kcal/mol. The negative electrostatic potential at the nitrogen and dianionic pyridine-2,6-dicarboxylate regions confirms that these are dynamic locations for Yb(III) binding.

Electron transfer photochromism of Ln-based (Ln = Dy, Tb) coordinated polymers for reversibly switching off/on single-molecule magnetic behavior

Switching on/off single-molecule magnets (SMMs) at room temperature is still a challenge in moleculebased magnets. Herein, two photochromic Ln-based (Ln = Dy, Tb) phosphonate coordinated polymers were synthesized with regulable SMM behavior. The reversible room-temperature photo-coloration was an electron transfer process with a generation of relatively stable radicals, characterized by structural analyses, ultraviolet-visible, luminescence and electron spin resonance spectra and magnetic measurements. Importantly, owing to the antiferromagnetic coupling interactions between Ln3+ ions and photogenerated radicals, the room-temperature light irradiation surprisingly switched off the SMM behavior, showing the first example of radicalquenched SMMs in the molecule-based magnets. Moreover, the silient SMM behavior could be recovered after eliminating photogenerated radicals via heat treatment, showing a reversible off/on switch of SMMs via light and heat. This work constructs a system for switching off/on SMMs through electron transfer photochromism, providing a visual operation way via naked-eye-detectable coloration for the switchable SMMs.

Mn2+ substitution within the {V14As8} polyoxovanadate archetype results in {Mn2V12As8} shells with trans‐positioned heterometal positions

AbstractSolvothermal exploration of the As, V, Mn reaction system in the presence of aqueous diethylenetriamine (=dien) solution led to the discovery of [MnII4VIV12AsIII8O40(dien)4(H2O)] ⋅ 3.5H2O, containing the first arsenato‐polyoxovanadate featuring a {Mn2V12As8O40} cluster shell. In comparison to its parental {V14As8O42} archetype, two vanadyl (VO2+) units at opposite ends of the polyoxovanadate shell here are substituted by Mn2+ centers. In the solid state, these {Mn2V12As8O40} units are joined into rods by sharing common Mn−O−V linkages. Expansion of the cluster shell by two further Mn2+ sites via Mn−O=V bridges generates a {Mn4V12As8O40} moiety. Three Mn2+ cations are joined by monodentate‐coordinating dien ligands, which link the rods into layers. The dien ligands here coexist in three different coordination modes: monodentate, bidentate and tridentate, which is rarely observed. Magnetic susceptibility measurements show the expected significant antiferromagnetic coupling interactions between all spin centers present in the title compound, namely the isotropic spin‐5/2 Mn2+ centers and the isotropic spin‐1/2 vanadyl groups, in line with most other heterometal‐substituted arsenato‐polyoxovanadate(IV) clusters.

Two-Dimensional Nitronyl Nitroxide–Cu Networks Based on Multi-Dentate Nitronyl Nitroxides: Structures and Magnetic Properties

Two multi-dentate nitronyl nitroxide radicals, namely, bisNITPhPy ([5-(4-pyridyl)-1,3-bis(1′-oxyl-3′-oxido-4′,4′,5′,5′-tetramethyl-4,5-hydro-1H-imidazol-2-yl)]benzene) and NIT-3Py-5-4Py (2-{3-[5-(4-pyridyl)]pyridyl}-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide), were assembled with CuII ions to obtain two-dimensional heterospin 2p–3d coordination polymers [Cu7(hfac)14(bisNITPhPy)2]n (1) and [Cu2(hfac)4(NIT-3Py-5-4Py)]n (2) (hfac: hexafluoroacetylacetonate). In both compounds, the bisNITPhPy and NIT-3Py-5-3Py radicals acted as pentadentate and tetradentate ligands, respectively, to connect with CuII ions, generating a 2D layer structure. The analysis of the magnetic behavior indicated that strong antiferromagnetic coupling and ferromagnetic interaction (J = 17.1 cm−1) coexisted in 1. For 2, there were ferromagnetic couplings between the CuII ion and NO group, as well as the CuII ion and radical via the pyridine ring with J1 = 32.8 and J2 = 2.2 cm−1, respectively.

RETRACTED: Two mixed-ligand coordination polymers: Magnetic properties and biological evaluation on myofascial pain syndrome by reducing IL-6 release

Two coordination polymers (CPs) based on Co(II) and Cu(II) ions as metal centers were produced via alternation of auxiliary polycarboxylates with solvothermal reactions between corresponding metal salts and 3,3′,5,5′-tetra(1 H -imidazole-1-yl)-1,1′-biphenyl (L), and their chemical formulae are [Cu 2 (L)(2,6-NDC)(OAc) 2 ]·2H 2 O ( 1 ) and [Co 2 (L)(BPnDC) 2 ]·6H 2 O ( 2 ) (H 2 BPnDC ​= ​4,4′-carbonyldibenzoic acid and 2,6-H 2 NDC ​= ​2,6-naphthalic acid). The two compounds’ magnetic performances suggested antiferromagnetic coupling interactions between the adjacent metal ions. Their protective activity on myofascial pain syndrome was assessed, and their specific mechanism was studied simultaneously. First, enzyme-linked immunosorbent assay detection was carried out to assess the inflammatory cytokine TNF-α and IL-6 levels released from fascial cells. Then, the activation of inflammatory response in fascial cells was measured through real-time reverse transcription–polymerase chain reaction by evaluating the p53 and nf-κb relative expression levels after treatment with the compound. A hemolysis test was conducted to evaluate the safety of the new compounds, and CCK-8 assay was finished to explore the cytotoxicity of compounds 1 and 2 . • Two coordination polymers were produced. • Antiferromagnetic coupling interactions were found between the adjacent metal ions. • Their protective activity on the myofascial pain syndromes was assessed.

A 1D Mn-based coordination polymer with significant magnetocaloric effect

A 1D Mn-containing coordination polymer (CP) has been prepared by the hydrothermal assembly of MnCl2·4H2O with Hcptpy and H2bdc (Hcptpy = 4-(4-carboxyphenyl)-2,2′:4′,4″-terpyridine, H2bdc = 1,4-benzenedicarboxylic acid), [Mn(cptpy)Cl(H2O)(DMF)]n (1), which is further structurally characterized by different methods including X-ray single-crystal diffraction, elemental analysis, infrared (IR) spectrum, thermogravimetric (TG) analysis, and powder X-ray diffraction (PXRD). Structural analysis indicates that the asymmetric skeleton of 1 consists of one Mn2+ ion, one cptpy– ligand, one Cl– anion, one coordinated H2O and one DMF. Each six-coordinated Mn2+ ion in 1 is alternately connected by carboxyl O atoms and pyridine N atoms of cptpy– ligands to present a 1D chain, which could be further stacked to produce a 3D supramolecular structure through hydrogen bonds and π···π stacking interactions. Magnetic results suggest that the presence of antiferromagnetic coupling interactions among Mn2+ ions in 1. Furthermore, 1 exhibits significant magnetocaloric effect (MCE) with the maximum –ΔSm value of 26.3 J·kg−1·K−1 at 2.0 K for an applied field of 70 kOe.

Synthesis, Structure, and Oxidative Reactivity of a Class of Thiolate‐Bridged Dichromium Complexes Featuring Antiferromagnetic Coupling Interactions

AbstractSeveral thiolate‐bridged dichromium complexes with Cp* (Cp*=η5‐C5Me5) as auxiliary ligands were designed and synthesized through the salt metathesis, which all contain two six‐coordinate chromium centers in the formal valence of +3. These complexes are all paramagnetic species, which are in good agreement with the experimental results that broad and paramagnetically shifted proton resonances appear in the 1H NMR spectra. Furthermore, variable‐temperature solid‐state magnetic susceptibility studies reveal the two chromium centers of these complexes are both in an S=3/2 high‐spin state with a strong antiferromagnetic coupling. Simulated values of antiferromagnetic coupling constant for these complexes are directly related to the distances of the two CrIII centers confirmed by X‐ray crystallography. In addition, in the presence of dehalogenation agent AgPF6, complexes [Cp*CrCl(μ‐SR)2CrClCp*] (3, R=Et; 4, R=iPr) and [Cp*Cr(μ‐Cl)(μ‐SEt)2CrCp*][BPh4] (5) containing easily removable chloride can achieve the catalytic oxidation of organic substrates, such as PPh3, 1,4‐cyclohexadiene and 1,2‐diphenylhydrazine under an oxygen atmosphere.

Modulation of Nuclearity in CuII -MnII Complexes of a N2 O2 Donor Ligand Depending upon Carboxylate Anions: Structures, Magnetic Properties and Catalytic Oxidase Activities.

Three new hetero-metallic copper(II)-manganese(II) complexes, [(CuL)2 Mn3 (C6 H5 CO2 )6 ] (1), [(CuL)2 Mn(CH3 CO2 )2 ] (2), and {[(CuL)2 Mn(C6 H5 CH2 CO2 )2 ] ⋅ 2CH3 CN} (3), have been synthesized using [CuL] as ''metalloligand'' (where H2 L=N,N'-bis(2-hydroxynaphthyl-methylidene)-1,3-propanediamine). Single-crystal structural analyses show an almost linear penta-nuclear structure for complex 1 where a square planar [CuL] unit is connected to each of the two terminal MnII ions of a linear, centrosymmetric [Mn3 (benzoate)6 ] unit through the double phenoxido bridges. Both complexes 2 and 3 possess a linear tri-nuclear structure where two terminal square-pyramidal [CuL] units are bonded to the central MnII ion through double phenoxido oxygen atoms along with a syn-syn bridging acetate (for 2)/phenyl acetate (for 3). All three complexes exhibit catecholase, and phenoxazinone synthase-like activities under aerial conditions. For catecholase like activity, the turnover numbers (kcat ) are 595, 40, and 205 h-1 whereas, for phenoxazinone synthase like activity, the turnover numbers are 25, 4, and 11 h-1 for complexes 1-3, respectively. The mechanism of both catalytic oxidase activities is proposed on the basis of mass spectral evidences. Variable-temperature (2-300 K) dc molar magnetic susceptibility measurements of 1 reveal antiferromagnetic interactions between the Cu-Mn centres (J1 =-29.3 cm-1 ), and also between the Mn-Mn centres of the [Mn3 (benzoate)6 ] unit (J2 =-0.68 cm-1 ). On increasing the magnetic field at 2 K, its ground spin state changes from S=3/2 to S=5/2 at 4 T, attributable to the low value of J2 which makes the excited spin states close in energy with the ground spin state. Complexes 2 and 3 show antiferromagnetic coupling interactions between the Cu-Mn pairs with J values of -9.51, and -5.32 cm-1 , respectively.

Two series of novel Ln2Mn and Ln6Mn2 (Ln = Gd/Tb) clusters: Synthesis, structures and magnetic properties

Two linear Ln-Mn(III) clusters were obtained with the formulae of [Gd2Mn(H2TEOA)4(C7H5O2)2](NO3)3·4(H2O) (1) and [Tb2Mn(H2TEOA)4(C7H5O2)2](C7H5O2)2(NO3)·(H3TEOA)·5(H2O) (2) in the presence of the mixed ligands of triethanolamine (H3TEOA) and benzoic acid. The multidentate ligand 2,2-bis(hydroxymethyl)butyric acid (H3L) and benzoic acid as mixed ligands, two neutral Ln-Mn(III) clusters were prepared with the formulae of [Ln6Mn2(L)4(H2L)4(C7H5O2)4(C2H5OH)2(NO3)4(H2O)4]·(CH3CN)·24(H2O) (Ln = Gd for 3, Ln = Tb for 4, H3L = 2,2-bis(hydroxymethyl)butyric acid). Single X-ray analysis showed that three metal ions of compounds 1–2 were located on a straight line and eight metal ions of compounds 3–4 were on a coplanar plane, forming a quadrilateral arrangement. Magnetic data indicated that compounds 1–4 all exhibited obvious antiferromagnetic properties. The results of Quantum Monte Carlo (QMC) calculation of compound 3 showed that four magnetic coupling interactions of J1 = –0.401(5) cm−1, J2 = 0.370(7) cm−1 for Gd⋯Mn and J3 = −0.498(7) cm−1, J4 = 0.711(7) cm−1 for Gd⋯Gd were present. The values of −0.401(5) cm−1 for J1 and −0.498(7) cm−1 for J3 suggested that the antiferromagnetic coupling interactions of Gd⋯Mn and Gd⋯Gd in the low temperature region were dominant in 3.

Magnetic transition behavior and large topological Hall effect in hexagonal Mn2−xFe1+xSn (x = 0.1) magnet

The magnetic transition, transport properties, and magnetic domain structures of the polycrystalline Mn1.9Fe1.1Sn compound with a hexagonal structure have been investigated. The result shows that ferromagnetic and antiferromagnetic phases coexist in this compound. A large topological Hall effect up to 3.5 μΩ·cm at 50 K has been found due to the formation of noncoplanar spin structures when the competition occurs among magnetocrystalline anisotropy, antiferromagnetic coupling, and ferromagnetic interaction at low temperature. The result of in situ Lorentz transmission electron microscopy cooling experiment at zero field indicates two shapes of domain walls containing vortexes coexisting simultaneously in the compound.

A bell-like 15-metallacrown-5 complex from flexible H2Glyha ligand: Synthesis, structure and filed-induced slow magnetic relaxation

The reaction of Glycinehydroxamic acid (H2glyha) ligand, Cu(OAc)2·H2O and Dy(NO3)3·6H2O afforded an intriguing bell-like 15-Metallacrown-5 complex [Dy(OAc)Cu5(glyha)5(H2O)4]·2NO3·4H2O, which exhibit a cyclic [CuGly]5 frame and a Dy(III) ion is located at the center of the ring with the help of ring five oxygen atoms in the equatorial plane. Magnetic studies reveal complex 1 shows antiferromagnetic coupling interactions and field-induced slow magnetic relaxation.

Spontaneous magnetic bubbles and large topological Hall effect in Mn3-xFexSn compound

Magnetic and transport properties as well as magnetic domain structures have been investigated in a hexagonal polycrystalline Mn2.1Fe0.9Sn compound. The in-situ observation of Lorentz transmission electron microscopy shows that spontaneous magnetic bubbles owing a pair of Bloch lines and biskyrmions consisting of two skyrmions of opposite spin helicities coexist in this compound at low temperature. A large topological Hall resistivity up to about 9 µΩ·cm at 50 K has been found owing to the formation of noncoplanar spin textures deriving from the competition among magnetocrystalline anisotropy, antiferromagnetic coupling, and ferromagnetic interaction.

3d–4f Metallacrown complexes with a new sandwich core: synthesis, structures and single molecule magnet behavior

Two heterometallic metallacrown complexes, [Er{Cu4(butyrat)4}2]·Cl3·MeOH·26H2O (1) and [Yb{Cu4(butyrat)4}2]·Cl3·MeOH·26H2O (2) (H2butyrat = 3-aminobutyric hydroxamic acid), have been reported.