Dominant Ferromagnetic Interactions Research Articles

Experimental studies on noncentrosymmetric Nd3Se4: Strongly correlated noncollinear ferromagnet

We have synthesized polycrystalline Nd3Se4 by the solid state sealed tube reaction route followed by structural characterization and magnetic property measurements. The temperature-dependent magnetization studies reveal the existence of competing magnetic interactions below the ferromagnetic ordering (TC ≈ 48.4 K). The observation of hysteresis in the isothermal magnetization M(H) data with the coercive field of ≈ 0.25 T at 2 K indicates dominant ferromagnetic interactions in the applied field. The nonsaturating behavior of M(H) data at higher applied field and kinks in corresponding dM/dHvs. H plots suggest the coexistence of multiple magnetic interactions at low temperatures. Using the M(T,H=2 T) data, the Rhodes-Wohlfarth ratio (qc/qs) has been estimated to be ≈ 3.6, which supports the itinerant magnetism in Nd3Se4. These competing interactions have been further investigated by AC-susceptibility measurements at various excitation frequencies. The χ′ reduces drastically with an increase in the applied DC field, as observed from isothermal field-dependent AC-χ studies. Additionally, the strong correlation between delocalized charge and localized magnetic moments is evident from ρ(T) measurements at H = 0 and 5 T. The ρ(T,H=0 T) data shows a clear drop having quadratic temperature dependence, below TC. Furthermore, the inter-dependence between electrical transport and magnetism has been established firmly through negative magnetoresistance, in which the maxima correspond to the coercive field obtained from M(H) data.

Designer Spin Models in Tunable Two-Dimensional Nanographene Lattices.

Motivated by recent experimental breakthroughs, we propose a strategy for designing two-dimensional spin-lattices with competing interactions that lead to nontrivial emergent quantum states. We consider S = 1/2 nanographenes with C3 symmetry as building blocks, and we leverage the potential to control both the sign and the strength of exchange with first neighbors to build a family of spin models. Specifically, we consider the case of a Heisenberg model in a triangle-decorated honeycomb lattice with competing ferromagnetic and antiferromagnetic interactions whose ratio can be varied in a wide range. On the basis of the exact diagonalization of both Fermionic and spin models, we predict a quantum phase transition between a valence bond crystal of spin singlets with triplon excitations living in a Kagomé lattice and a Néel phase of effective S = 3/2 in the limit of dominant ferromagnetic interactions.

Effect of Al3+ substitution on the magnetodielectric properties of the one-dimensional frustrated Ca3Co2O6

Ca3Co2-xAlxO6 (x = 0, 0.02, 0.04, 0.06, 0.08 and 0.1) were prepared via the conventional sol-gel method. The structure, magnetic, dielectric and magnetodielectric properties were investigated. The Rietveld structural refinement confirms the rhombohedral structure of the samples. The positive Curie-Weiss temperature θ and magnetic coupling exchange constants J indicate the dominant intrachain ferromagnetic interactions in the spin chains. The obvious inhibition effect to equally spaced magnetization steps demonstrates that Al3+ could release the magnetic frustration. With Al3+ substitution, both the magnetization intensity and the critical field of the ferrimagnetism to ferromagnetism transition decrease. The samples present obvious dielectric anomalies around the Curie temperature Tc and the freezing temperature Tf. Meanwhile, the magnetic field dependence of dielectric permittivity decreases suddenly at critical magnetic fields. These results reveal strong magnetodielectric coupling effect in Ca3Co2-xAlxO6. The same sign of Δεr and Δtanδ suggests that the magnetodielectric coupling effect is intrinsic.

Momentum-independent magnetic excitation continuum in the honeycomb iridate H3LiIr2O6

Understanding the interplay between the inherent disorder and the correlated fluctuating-spin ground state is a key element in the search for quantum spin liquids. H3LiIr2O6 is considered to be a spin liquid that is proximate to the Kitaev-limit quantum spin liquid. Its ground state shows no magnetic order or spin freezing as expected for the spin liquid state. However, hydrogen zero-point motion and stacking faults are known to be present. The resulting bond disorder has been invoked to explain the existence of unexpected low-energy spin excitations, although data interpretation remains challenging. Here, we use resonant X-ray spectroscopies to map the collective excitations in H3LiIr2O6 and characterize its magnetic state. In the low-temperature correlated state, we reveal a broad bandwidth of magnetic excitations. The central energy and the high-energy tail of the continuum are consistent with expectations for dominant ferromagnetic Kitaev interactions between dynamically fluctuating spins. Furthermore, the absence of a momentum dependence to these excitations are consistent with disorder-induced broken translational invariance. Our low-energy data and the energy and width of the crystal field excitations support an interpretation of H3LiIr2O6 as a disordered topological spin liquid in close proximity to bond-disordered versions of the Kitaev quantum spin liquid.

Coupling of magnetism, crystal lattice, and transport in EuCuP and EuCuAs

EuCuP and EuCuAs are members of a family of materials with candidates for realizing magnetically tuned electronic topology. In this work, the magnetic phase transitions and magnetoelastic coupling of EuCuP and EuCuAs have been investigated. Around the Curie temperature, the thermal expansion coefficient and specific-heat capacity of EuCuP are found to have two closely spaced features, at approximately 30 and 31.3 K, which may indicate a cascading magnetic transition or perhaps an electronic transition closely coupled to the magnetic ordering. The zero-field magnetoelastic coupling appears to be stronger in EuCuP than in EuCuAs, and field-dependent measurements suggest this is due to the dominant ferromagnetic interaction in EuCuP as opposed to antiferromagnetic order in EuCuAs below ${T}_{\mathrm{N}}=13.5\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. Thermal expansion is anisotropic around ${T}_{\mathrm{N}}$ in EuCuAs, with a maximum expansion along [001] occurring above ${T}_{\mathrm{N}}$ prior to a stiffening of this $c$-axis component on cooling through ${T}_{\mathrm{N}}$; the expansion of the basal plane has a lambda-like peak centered slightly above ${T}_{\mathrm{N}}$. Matching these behaviors, the ac susceptibility data for EuCuAs suggest the presence of strong ferromagnetic correlations above ${T}_{\mathrm{N}}$ in the vicinity where the $c$-axis expansion peaks. Both compounds possess similar electrical and thermoelectric transport behaviors, with short-range magnetic order likely playing an important role above ${T}_{\mathrm{C}}$ or ${T}_{\mathrm{N}}$. Transport properties suggest these are predominantly hole doped due to intrinsic defects, and narrow-gap semiconducting or semimetallic behavior may be achievable if the underlying defects can be tuned.

Magnetic properties of the quasicrystal approximant Au65Ga21Tb14

The magnetic properties of the quasicrystal approximant ${\mathrm{Au}}_{65}{\mathrm{Ga}}_{21}{\mathrm{Tb}}_{14}$ were investigated using magnetization and neutron diffraction experiments. The temperature dependences of the magnetic susceptibility and magnetization curve indicate dominant ferromagnetic interactions, whereas a whirling antiferromagnetic order was observed in neutron diffraction experiments. In the antiferromagnetic phase, the magnetic moments are aligned almost perpendicular to a pseudofivefold symmetry axis, which corresponds to the easy-axis direction of a Tb atom. Magnetic properties similar to those of ${\mathrm{Au}}_{72}{\mathrm{Al}}_{14}{\mathrm{Tb}}_{14}$ in spite of the substantial difference in the Au concentration suggest the robustness of the easy-axis anisotropy against the chemical environment.

How does thickness affect magnetic coupling in Ti-based MXenes.

The magnetic nature of Ti2C, Ti3C2, and Ti4C3 MXenes is determined from periodic calculations within density functional theory and using the generalized gradient approximation based PBE functional, the PBE0 and HSE06 hybrids, and the on-site Hubbard corrected PBE+U one, in all cases using a very tight numerical setup. The results show that all functionals consistently predict a magnetic ground state for all MXenes, with spin densities mainly located at the Ti surface atoms. The analysis of solutions corresponding to different spin orderings consistently show that all functionals predict an antiferromagnetic conducting ground state with the two ferromagnetic outer (surface) Ti layers being antiferromagnetically coupled. A physically meaningful spin model is proposed, consistent with the analysis of the chemical bond, with closed shell, diamagnetic, Ti2+ like ions in inner layers and surface paramagnetic Ti+ like centers with one unpaired electron per magnetic center. From a Heisenberg spin model, the relevant isotropic magnetic coupling constants are extracted from an appropriate mapping of total energy differences per formula unit to the expected energy values of the spin Hamiltonian. While the numerical values of the magnetic coupling constants largely depend on the used functional, the nearest neighbor intralayer coupling is found to be always ferromagnetic, and constitutes the dominant interaction, although two other non-negligible interlayer antiferromagnetic terms are involved, implying that the spin description cannot be reduced to NN interaction only. The influence of the MXene thickness is noticeable for the dominant ferromagnetic interaction, increasing its value with the MXene width. However, the interlayer interactions are essentially due to the covalency effects observed in all metallic solutions which, as expected, decay with distance. Within the PBE+U approach, a U value of 5 eV is found to closely simulate the results from hybrid functionals for Ti2C and less accurately for Ti3C2 and Ti4C3.

Observation of griffiths phase and ferromagnetism in LaFe0.5Mn0.5O3

We report the structural and magnetic characterization of the polycrystalline LaFe0.5Mn0.5O3 compound. It crystallizes in an orthorhombic crystal structure with Pnma space group. A systematic investigation of magnetic behavior revealed the antiferromagnetic ordering at 276 K and Griffiths Phase-like behavior in the temperature range of 276 K to 314 K, confirmed by the power-law susceptibility exponent(λ). At a low temperature, spontaneous magnetization (Ms) is due to dominant ferromagnetic interaction. We estimated the magnitude using Arrot plot of different isotherms.

Slow spin dynamics of cluster spin-glass spinel Zn(FeRu x )2O4: role of Jahn–Teller active spin-1/2 Cu2+ ions at B-sites

We report the slow spin dynamics of cluster spin-glass (SG) spinel Zn(FeRu x )2O4 by means of detailed -magnetization and -susceptibility studies combined with the heat capacity analysis. Two specific compositions (x = 0.5, 0.75) have been investigated in detail along with the substitution of Jahn–Teller (JT) active spin-1/2 Cu2+ ions at B-sites. Measurements based on the frequency and temperature dependence of -susceptibility () and the subsequent analysis using the empirical scaling laws such as: (a) Vogel–Fulcher law and (b) Power law reveal the presence of cluster SG state below the characteristic freezing temperature (17.77 K (x = 0.5) and 14 K (x = 0.75)). Relaxation dynamics of both the compositions follow the non-mean field de Almeida–Thouless (AT)-line approach , with an ideal value of φ = 3. Nevertheless, the analysis of temperature dependent high field -susceptibility, (, T) provides evidence for Gabay–Toulouse type mixed-phase (coexistence of SG and ferrimagnetic (FiM)) behaviour. Further, in the case of Cu0.2Zn0.8FeRuO4 system, slowly fluctuating magnetic clusters persist even above the short-range FiM ordering temperature () and their volume fraction vanishes completely across ∼6. This particular feature of the dynamics has been very well supported by the time decay of the thermoremanent magnetization and heat-capacity studies. We employed the high temperature series expansion technique to determine the symmetric exchange coupling () between the spins which yields eV for Cu0.2Zn0.8FeRuO4 representing the dominant intra-sublattice ferromagnetic interactions due to the dilute incorporation of the JT active Cu2+ ions. However, the antiferromagnetic coupling is predominant in ZnFeRuO4 and Cu0.2Zn0.8Fe0.5Ru1.5O4 systems. Finally, we deduced the magnetic phase diagram in the plane using the characteristic parameters obtained from the field variations of both - and -magnetization measurements.

Tuning of magnetic properties in Cr-doped lithium ferrite

Cationic substitutions in lithium ferrite spinel (LiFe 5 O 8 ) leading to modifications in magnetic properties have a significant role in their technological applications. In this context, LiFe 5− x Cr x O 8 , compounds with 0 ≤ x ≤ 3 were synthesized and studied using X-ray diffraction, X-ray photoelectron spectroscopy (XPS), M o ¨ ssbauer spectroscopy and magnetization measurements. Oxidation states of Fe and Cr are found to be 3 + from XPS investigations and further confirmed from the M o ¨ ssbauer analysis. Cr replaces Fe from both tetrahedral and octahedral sites. Magnetization and magnetic ordering temperature decrease with increasing Cr concentration. This is consequent to reduced strength of dominant Fe - O - Fe interactions due to replacement of Fe with Cr cation possessing relatively smaller magnetic moment. The positive value of Curie-Weiss constant implies that the system has dominant ferromagnetic interactions. The much important negative magnetization and spin compensation phenomena are observed only in specific range of doping concentration (x = 2.5–3). Spin compensation in LiFe 2.5 Cr 2.5 O 8 occurs at 315 K, close to room temperature. • The effect of Cr doping on oxidation state of cations and their distribution at tetrahedral and octahedral sites is reported. • The influence of Cr doping on the magnetic properties of LiFe 5 O 8 is reported. • Spin compensation behavior is observed in LiFe 2.5 CR 2.5 O 8 and LiFe 2 CR 3 O 8 compounds.

Polar Ferromagnet Induced by Fluorine Positioning in Isomeric Layered Copper Halide Perovskites.

We present the influence of positional isomerism on the crystal structure of fluorobenzylammonium copper(II) chloride perovskites A2CuCl4 by incorporating ortho-, meta-, and para-fluorine substitution in the benzylamine structure. Two-dimensional (2D) polar ferromagnet (3-FbaH)2CuCl4 (3-FbaH+ = 3-fluorobenzylammonium) is successfully obtained, which crystallizes in a polar orthorhombic space group Pca21 at room temperature. In contrast, both (2-FbaH)2CuCl4 (2-FbaH+ = 2-fluorobenzylammonium) and (4-FbaH)2CuCl4 (4-FbaH+ = 4-fluorobenzylammonium) crystallize in centrosymmetric space groups P21/c and Pnma at room temperature, respectively, displaying significant differences in crystal structures. These differences indicate that the position of the fluorine atom is a driver for the polar behavior in (3-FbaH)2CuCl4. Preliminary magnetic measurements confirm that these three perovskites possess dominant ferromagnetic interactions within the inorganic [CuCl4]∞ layers. Therefore, (3-FbaH)2CuCl4 is a polar ferromagnet, with potential as a type I multiferroic. This work is expected to promote further development of high-performance 2D copper(II) halide perovskite multiferroic materials.

Structural Features in Some Layered Hybrid Copper Chloride Perovskites: ACuCl4 or A2CuCl4.

We present three new hybrid copper(II) chloride layered perovskites of generic composition ACuCl4 or A2CuCl4, which exhibit three distinct structure types. (m-PdH2)CuCl4 (m-PdH22+ = protonated m-phenylenediamine) adopts a Dion-Jacobson (DJ)-like layered perovskite structure type and exhibits a very large axial thermal contraction effect upon heating, as revealed via variable-temperature synchrotron X-ray powder diffraction (SXRD). This can be attributed to the contraction of an interlayer block, via a slight repositioning of the m-PdH22+ moiety. (3-AbaH)2CuCl4 (3-AbaH+ = protonated 3-aminobenzoic acid) and (4-AbaH)2CuCl4 (4-AbaH+ = protonated 4-aminobenzoic acid) possess the same generic formula as Ruddlesden-Popper (RP) layered perovskites, A2BX4, but adopt different structures. (4-AbaH)2CuCl4 adopts a near-staggered structure type, whereas (3-AbaH)2CuCl4 adopts a near-eclipsed structure type, which resembles the DJ rather than the RP family. (3-AbaH)2CuCl4 also displays static disorder of the [CuCl4]∞ layers. The crystal structures of each are discussed in terms of the differing nature of the templating molecular species, and these are compared to related layered perovskites. Preliminary magnetic measurements are reported, suggesting dominant ferromagnetic interactions.

Formation of Defect-Dicubane-Type NiII 2LnIII 2 (Ln = Tb, Er) Clusters: Crystal Structures and Modeling of the Magnetic Properties.

In the field of molecular nanoclusters, cubane and defect-dicubane, or butterfly structures, are typical examples of tetranuclear metal core architectures. In this work, a halogenated and anionic Schiff-base ligand (L2–) is utilized as it is predisposed to chelate within a cluster core to both 3d and 4f metal ions, in different binding configurations (H2L = 4-chloro-2-(2-hydroxy-3-methoxybenzyliden amino)phenol). The phenolate oxygen atoms of the deprotonated ligand can act in μ-O and μ3-O bridging binding modes for the intramolecular assembly of metal ions. Based on that, two tetranuclear and isostructural compounds [Ni2Tb2(L)4(NO3)2(DMF)2]·2CH3CN (1) and [Ni2Er2(L)4(NO3)2(DMF)2]·0.5CH3CN (2) were synthesized and structurally characterized. Magnetic susceptibility and magnetization data indicate the occurrence of dominant intramolecular ferromagnetic interactions between the spin centers. Particular emphasis is given to the theoretical description of the magnetic behavior, taking into account the Ln–Ni and Ni–Ni coupling paths and the magnetic anisotropy of the LnIII and NiII ions. The study is distinguished for its discussion of two distinct models, whereby model A relies on the uniaxial B20 Stevens term describing the lanthanide anisotropy and model B is based on point-charge model calculations. Importantly, the physical meaning of the obtained parameters for both models was critically scrutinized.

Synthesis, crystal structures, magnetic and magnetocaloric studies of heterometallic enneanuclear {Cu7Gd2} complexes

The reaction of Gd(NO3)3·6H2O and [Cu2(piv)4(pivH)2] with the polydentate Schiff base ligands o-OH-C10H6-CH = NC(R)(CH2OH)2 (R = CH3, H3L1; R = C2H5, H3L2) in MeOH afforded the enneanuclear heterometallic complexes [Cu7Gd2(L1)4(HL1)2(piv)4(H2O)(MeOH)3] (1) and [Cu7Gd2(L2)4(HL2)2(piv)4(MeOH)5] (2). Crystallographic studies revealed that both complexes are isostructural and consist of a central core {Cu7Gd2(μ3-Oalkoxo)6(μ2-Oalkoxo)4(μ2-Opivalato)2}8+. Peripheral ligation and bridging are provided by four triply and two doubly deprotonated Schiff base ligands, two μ3-pivalates, two chelate pivalates, and terminal aqua and/or MeOH molecules. Magnetic susceptibility measurements revealed the presence of dominant ferromagnetic intramolecular interactions in both complexes. The magnetocaloric effect of 1 and 2 was examined via isothermal magnetization measurements under various applied fields and the maximum entropy change was found equal to 13.3 and 12.1 Jkg-1K−1 for 1 and 2, respectively, at 2 K for ΔH = 5 T.

Vacancies and spin–phonon coupling in CrSi0.8Ge0.1Te3

AbstractWe report temperature‐dependent Raman scattering and magnetization studies of van der Waals ferromagnetic compound CrSi0.8Ge0.1Te3. Magnetic susceptibility measurements revealed dominant ferromagnetic interactions below TC which shift to the lower values due to the presence of vacancies. A Raman active mode, additional to the ones predicted by symmetry in the parent compounds, has been observed. This Ag symmetry mode most likely emerges as a consequence of the atomic vacancies on Si/Ge site. Presence of the strong spin–phonon coupling at temperature around 210 K is indicated by deviations from conventional phonon self‐energy temperature dependence of all analysed modes.

Crystal electric field effects and heavy-fermion behavior in cubic PrCu2Au3 compound

We report the crystal structure as well as the magnetic, electronic and transport properties of PrCu2Au3 which crystallizes in the MgCu4Sn-type structure with the cubic space group F4¯3m (No. 216). In this structure, the Pr3+ ion sits on a lattice site with the cubic Td symmetry which dictates the crystal electric field (CEF) splitting of the Hund’s 3H4 ground multiplet into four levels. The sample has been investigated by measurements of temperature dependences of specific heat, Cp(T), electrical resistivity, ρ(T), magnetic susceptibility, χ(T), isothermal magnetization, M(B,T), thermal conductivity, κT(T) and thermoelectric power, S(T). χ(T) follows a Curie-Weiss behavior above 100 K with an effective magnetic moment, μeff = 3.3 μB/Pr which is comparable to a calculated value of 3.58 μB/Pr for a free Pr3+ ion and a Weiss temperature, θCW = 15.70 K indicating a dominant ferromagnetic interaction. From the analysis of M(B,T) and the 4f-electron derived specific heat (C4f(T)) results, the CEF ground state is a Γ5 magnetic triplet and the CEF energy scheme is presented. The Sommerfeld coefficient, γ estimated from the low-temperature C4f(T) is 304 mJ/(mol K2) indicating a mass enhancement of the conduction electrons at low temperatures. Further analysis of the heavy fermion properties based on the Sommerfeld-Wilson ratio supports the formation of a heavy fermion state in PrCu2Au3. However, the absence of an enhancement in S/T at low temperatures possibly suggests a weak correlation between the conduction electrons and the 4f-electrons at the Fermi energy. The thermal transport properties suggest that PrCu2Au3 is likely a compensated metal.

Long-Range Ferromagnetic Exchange Interactions Mediated by Mn-CeIV-Mn Superexchange Involving Empty 4f Orbitals.

Reactions involving reductive aggregation of MnO4- in methanol in the presence of CeIV and an excess of carboxylic acid have led to the synthesis of structurally related Ce/Mn clusters, [Ce3Mn5O8(OMe)(O2CBut)13(MeOH)] (1) and [Ce2Mn3O5(O2CPh)9(MeOH)3] (2), containing at least one {Mn2Ce2O4} cubane unit. The cores of both clusters contain Mnx units separated by three (1) or two (2) CeIV ions. Fits of variable-temperature, solid-state dc and ac magnetic susceptibility data reveal dominant ferromagnetic interactions within 1 and 2, resulting in the maximum S = 17/2 and S = 5 ground state spins, respectively, and thus suggesting significant ferromagnetic (F) interactions between the Mnx units that are ≥6 Å apart and separated by four intervening bonds through diamagnetic CeIV. Fits of magnetic susceptibility data also revealed unusual long-range F interactions, and this finding was further supported by high-field EPR measurements and simulations. Density functional theory calculations and a Wannier function analysis confirm long-range interactions and indicate a Mn-Ce-Mn superexchange pathway via Mn-d/Ce-f orbital overlap/hybridization.

Correlation of exchange-bias effect with negative magnetization in perovskite compound, La0.5Pr0.5CrO3

Detailed investigations of the negative magnetization (NM) phenomenon and associated exchange bias (EB) effect in a single phase perovskite compound, La0.5Pr0.5CrO3, have been carried out. DC magnetization measurement under 200 Oe reveals a magnetic ordering (TN) at 264 K and a magnetization compensation at temperature, TCOMP ∼ 160 K. The compound exhibits NM as well as EB below TCOMP. The temperature and cooling field dependencies of EB have been investigated to reveal the dominant antiferromagnetic (AFM) and ferromagnetic (FM) interactions in La0.5Pr0.5CrO3. Both positive horizontal (HEB) and negative vertical (MEB) shifts (with respect to the origin) of field-cooled hysteresis curves are observed. Interestingly, both magnetization and EB (HEB and MEB) become zero at TCOMP. In addition, the EB (HEB and MEB) effect is maximum for a cooling field of 5 kOe, which is also the maximum field for observing NM behavior in La0.5Pr0.5CrO3, indicating a correlation between EB and NM. Rietveld refined neutron diffraction patterns at various temperatures infer a Gy type AFM ordering of Cr3+ moments below TN. Both NM and positive EB phenomena have been explained by considering the AFM exchange interaction between an induced moment of Pr3+ and a FM component of canted Cr3+ moment. The understanding is significant as it may open up the possibility for making thermomagnetic switches, magnetic memory, and other spintronic devices.

Uncovering the Triplet Ground State of Triangular Graphene Nanoflakes Engineered with Atomic Precision on a Metal Surface.

Graphene can develop large magnetic moments in custom-crafted open-shell nanostructures such as triangulene, a triangular piece of graphene with zigzag edges. Current methods of engineering graphene nanosystems on surfaces succeeded in producing atomically precise open-shell structures, but demonstration of their net spin remains elusive to date. Here, we fabricate triangulenelike graphene systems and demonstrate that they possess a spin S=1 ground state. Scanning tunneling spectroscopy identifies the fingerprint of an underscreened S=1 Kondo state on these flakes at low temperatures, signaling the dominant ferromagnetic interactions between two spins. Combined with simulations based on the meanfield Hubbard model, we show that this S=1 π paramagnetism is robust and can be turned into an S=1/2 state by additional H atoms attached to the radical sites. Our results demonstrate that π paramagnetism of high-spin graphene flakes can survive on surfaces, opening the door to study the quantum behavior of interacting π spins in graphene systems.

Ferromagnetic coupling in two tetranuclear Ni(II) complexes with cubane–like Ni4(μ3–O)4 core: Structure, spectroscopic and luminescence properties

Two new tetranuclear [Ni4(L1)4(MeOH)4] (1) and [Ni4(L2)4(EtOH)(MeOH)(H2O)2]·H2O (2) complexes have been synthesized by solvothermal method. We here report the spectroscopic, structural, photoluminescence and magnetic properties of both complexes. Complex 1 and 2 exhibit a cubane-like Ni4O4 structure. All Ni(II) center has a slightly distorted octahedral geometry. The optical properties of 1 and 2 have been analyzed by photoluminescence spectra obtained in the visible region. Variable-temperature (2–300 K) magnetic studies have been analyzed by using the Heisenberg Hamiltonian model with 2J exchange pathways. The best–fit parameters in analysis of the magnetic data are found as J1 = −2.38 cm−1, J2 = +5.43 cm−1, g = 2.2, Nα = 0.08 for 1, J1 = −2.34 cm−1, J2 = +4.90 cm−1, g = 2.2 and Nα = 0.11 for 2. These results are shown dominant ferromagnetic interactions between Ni(II) centers. Finally, the strong luminescence emission of both complexes makes them potentially useful photoactive material in developing optical and electronic materials.