Intrachain Ferromagnetic Interactions Research Articles

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.

Syntheses of two copper(II) coordination polymers from a morpholine-based tridentate Schiff base ligand: crystal structures and magnetic properties

Two new one-dimensional (1-D) end-to-end azido and thiocyanato bridged Cu(II) coordination polymers, [Cu(L)(µ-1,3-N3)] n (ClO4) n (1) and [Cu(L)(µ-1,3-NCS)] n (ClO4) n (2) with a morpholine-based tridentate N,N,N-donor Schiff base ligand (1-methyl-1H-imidazol-2-yl)-N-[2-(morpholin-4-yl)ethyl]methanimine, L) have been synthesized. Compounds 1 and 2 have been characterized by elemental analyses and spectroscopic techniques. The X-ray single crystal structures of 1 and 2 show the formation of regular zigzag chains with µ-1,3-azido and µ-1,3-thiocyanate bridges, respectively. Variable temperature (2–300 K) magnetic studies indicate that 1 shows a ferromagnetic intrachain exchange interaction with g = 2.135(2) and J = 2.13(2) cm−1, while in 2 this interaction is antiferromagnetic with g = 2.1412(3) and J = –0.277(2) cm−1. X-band EPR spectra of 1 and 2 in frozen (143 K) DMF solution corroborate our magnetic studies.

Carbon dioxide uptake by [Cu(bpca)]+: synthesis, crystal structure, and magnetic properties of {[Na(H2O)2][Cu2(bpca)2(CO3)(HCO3)]}n [Hbpca = bis(2-pyridylcarbonyl)amide

Carbon dioxide fixation by [Cu(bpca)(H2O)]2+ resulted in a chain having CO32− and HCO3− as ligands that shows a weak intrachain ferromagnetic interaction.

Experimental and theoretical investigation of structure-magnetic properties relationships in a new heteroleptic one-dimensional triple bridged azido/acetato/DMSO copper (II) coordination polymer

We report the synthesis, structure, and magnetic investigation of a novel one-dimensional copper (II) coordination polymer: formula [Cu(μ1,1N3)(μ1,3OAc)(μ-DMSO)]∞ (1) (OAc=acetate). The connection between neighbouring copper ions arises through a triple bridge involving EO type azide, syn–syn carboxylate and μ-DMSO molecule in apical positions forming an elongated octahedral coordination of copper ions. Magnetic susceptibility measurements show that complex (1) exhibits ferromagnetic intrachain interactions Jchain = +66 cm−1 whereas a metamagnetic behaviour occurs below 2.1 K related with antiferromagnetic inter-chain interactions with a critical field of 600 Oe at 1.8 K. DFT calculations were caried out to rationale the in-chain ferromagnetic interactions between copper ions. We found that the ferromagnetic coupling between copper ions is less sensitive to variation of bond length and/or Cu-N-Cu angle that may be caused by external stimulus such as temperature or pressure.

Ligand Modified and Light Switched On/Off Single-Chain Magnets of {Fe 2 Co} Coordination Polymers via Metal-to-Metal Charge Transfer

Ligand Modified and Light Switched On/Off Single-Chain Magnets of {Fe ₂ Co} Coordination Polymers via Metal-to-Metal Charge Transfer

Structure diversity and magnetic properties of manganese and cobalt coordination polymers with multiple carboxyl bridges

Based on asymmetric lithium salts of 1-(2-pyridinylmethyl)-pyrazole-3,5-dicarboxylate (2-Li2pmpd) or 1-(4-pyridinylmethyl)-pyrazole-3,5-dicarboxylate (4-Li2pmpd), four polymers [Mn(2-pmpd)(H2O)]n (1), {[Mn2(4-pmpd)(pd)(H2O)3]·H2O}n (2), [Co(4-pmpd)(H2O)]n (3) and [Co(2-pmpd)(H2O)2]n (4) [pd = pyrazole-3,5-dicarboxylate] have been hydrothermally prepared and characterized structurally. 1 displays three-dimensional (3D) network with (44.84) topology, 2 and 3 show 2D framework with (42·5·63)(42·52·64·72)(52·8) and (43)2(46·66·83) topologies, respectively. 4 is a 1D chain structure. Magnetization data of 1 with the 1D carboxylate bridges chain structure, fitted by the 1D model, suggests the antiferromagnetic coupling with J = −2.07 cm−1. The carboxylate bridges in 1 adopt common syn-syn and unidentate oxygen-bridge modes. 2 with the Mn4 unit, exhibits antiferromagnetic coupling with J = −0.68 cm−1 and zJ′ = −0.317 cm−1. The carboxylate bridges in 2 adopt common syn-anti and the unidentate oxygen-bridge modes. In the Co2 units, magnetization data for 3 shows the weak antiferromagnetic coupling. Variable temperature magnetic studies of 4 reveal ferromagnetic intrachain interactions and antiferromagnetic interchain magnetization interactions. The M(H) curves for 3 and 4 are consistent with their antiferromagnetic or ferromagnetic natures.

Magnetic interactions controlled by light in the family of Fe(II)-M(IV) (M = Mo, W, Nb) hybrid organic-inorganic frameworks.

Three new hybrid organic-inorganic frameworks employing octacyanidometallates and 4,4'-bypiridine dioxide (4,4'-bpdo) as bridging molecules were prepared and characterized. The three-dimensional coordination frameworks {[FeII(μ-4,4'-bpdo)(H2O)2]2[MIV(CN)8]·9H2O}n (Fe2Mo, Fe2W and Fe2Nb; M = Mo, W and Nb) are composed of cyanido-bridged chains, which are interconnected by the organic linkers. Magnetic measurements for Fe2Nb show a two-step transition to the antiferromagnetic state, which results from the cooperation of antiferromagnetic intra- and inter-chain interactions. Fe2Mo and Fe2W, on the other hand, behave as paramagnets at 2 K because of the diamagnetic character of the corresponding octacyanidometallate(IV) building units. However, after 450 nm light irradiation they show transition to the metastable high spin MoIV or WIV states, respectively, with distinct ferromagnetic intrachain spin interactions, as opposed to the antiferromagnetic ones observed in the Fe2Nb framework.

Quasi-one-dimensional magnetic properties of NiNb2−xVxO6 compounds synthesized at high pressure in a nonstandard columbite-type structure

We report on the low-dimensional magnetic behavior of the series of compounds ${\mathrm{NiNb}}_{2\ensuremath{-}x}{\mathrm{V}}_{x}{\mathrm{O}}_{6}$ ($0\ensuremath{\le}x\ensuremath{\le}2$), with a columbite-type crystal structure stabilized at high pressure and temperature. Based on susceptibility, magnetization, and specific-heat measurements, the system is characterized as presenting quasi-one-dimensional magnetism, with ${\mathrm{Ni}}^{2+}$ magnetic moments that can be modeled as Ising spins, placed along zigzag chains in the crystal structure. The low-temperature phase is found to consist of an antiferromagnetic arrangement of ferromagnetic chains, and a metamagnetic transition to uniform ferromagnetic order is observed under magnetic fields slightly above ${\ensuremath{\mu}}_{0}H=1\phantom{\rule{4pt}{0ex}}\mathrm{T}$. We discuss the effects of substituting vanadium for niobium, maintaining the same crystal structure along the whole series of samples. In particular, the long-range magnetic order, most clearly seen for $x=0$, tends to be suppressed as the vanadium content is increased. The exchange interactions are quantified, revealing that the ferromagnetic intrachain interactions vary from about $7\phantom{\rule{4pt}{0ex}}\mathrm{K}$ for ${\mathrm{NiNb}}_{2}{\mathrm{O}}_{6}$ to $2\phantom{\rule{4pt}{0ex}}\mathrm{K}$ for ${\mathrm{NiV}}_{2}{\mathrm{O}}_{6}$, remaining one order of magnitude larger than the mean antiferromagnetic interchain coupling.

Magnetic ground state of the one-dimensional ferromagnetic chain compoundsM(NCS)2(thiourea)2(M=Ni,Co)

The magnetic properties of the two isostructural molecule-based magnets, Ni(NCS)$_{2}$(thiourea)$_{2}$, $S$ = 1, [thiourea = SC(NH$_2$)$_2$] and Co(NCS)$_{2}$(thiourea)$_{2}$, $S$ = 3/2, are characterised using several techniques in order to rationalise their relationship with structural parameters and ascertain magnetic changes caused by substitution of the spin. Zero-field heat capacity and muon-spin relaxation measurements reveal low-temperature long-range ordering in both compounds, in addition to Ising-like ($D < 0$) single-ion anisotropy ($D_{\rm{Co}} \sim$ -100 K, $D_{\rm{Ni}} \sim$ -10 K). Crystal and electronic structure, combined with DC-field magnetometry, affirm highly quasi-one-dimensional behaviour, with ferromagnetic intrachain exchange interactions $J_{\rm{Co}}\approx+4$ K and $J_{\rm{Ni}}\sim+100$ K and weak antiferromagnetic interchain exchange, on the order of $J'$ $\sim-0.1$ K. Electron charge and spin-density mapping reveals through-space exchange as a mechanism to explain the large discrepancy in $J$-values despite, from a structural perspective, the highly similar exchange pathways in both materials. Both species can be compared to the similar compounds $M$Cl$_2$(thiourea)$_4$, $M$ = Ni(II) (DTN) and Co(II) (DTC), where DTN is know to harbour two magnetic field-induced quantum critical points. Direct comparison of DTN and DTC with the compounds studied here shows that substituting the halide Cl$^-$ ion, for the NCS$^-$ ion, results in a dramatic change in both the structural and magnetic properties.

Variation of the Chain Geometry in Isomeric 1D Co(NCS)2 Coordination Polymers and Their Influence on the Magnetic Properties.

Two different isomers of [Co(NCS)2(4-chloropyridine)2]n (3C and 3L) were synthesized from solution and by thermal decomposition of Co(NCS)2(4-chloropyridine)2(H2O)2 (2), which show a different metal coordination leading to corrugated chains in 3C and to linear chains in 3L. Solvent mediated conversion experiments prove that 3C is thermodynamically stable at room temperature where 3L is metastable. Magnetic measurements reveal that the magnetic exchange in 3L is comparable to that observed for previously reported related chain compounds, whereas in 3C with corrugated chains, the ferromagnetic interaction within the chains is strongly suppressed. The magnetic ordering takes place at 2.85 and 0.89 K, for 3L and 3C, respectively, based on specific heat measurements. For 3L the field dependence of magnetic relaxations in antiferromagnetically ordered ferromagnetic chains is presented. In addition, 3L is investigated by FD-FT THz-EPR spectroscopy, revealing a ground to first excited state energy gap of 14.0 cm-1. Broken-symmetry DFT calculations for 3C and 3L indicate a ferromagnetic intrachain interaction. Ab initio CASSCF/CASPT2/RASSI-SO computational studies reveal significantly different single-ion anisotropies for the crystallographically independent cobalt(II) centers in 3C and 3L. Together with the geometry of the chains this explains the magnetic properties of 3C and 3L. The ab initio results also explain the weaker exchange interaction in 3C and 3L as compared to previously reported [Co(NCS)2(L)2]n compounds with linear chains.

Two azido-bridged homospin Fe(ii)/Co(ii) coordination polymers featuring single-chain magnet behavior.

Two azido-bridged homospin Fe(ii)/Co(ii) coordination polymers [Fe2(Bzp)2(N3)4]n (1) and [Co4(Bzp)4(N3)8·(MeOH)2]n (2) (bzp = 2-benzoylpyridine) are prepared, which consist of one-dimensional neutral chains with pure EO-azido (μ2-1,1-N3) bridges. Magnetically, both 1 and 2 exhibit considerable intrachain ferromagnetic interactions which benefit from the EO-azido bridging mode, leading to typical single-chain magnet (SCM) behavior under both the "infinite-size" and "finite-size" regime and pronounced hysteresis loops. As far as the bridging network is concerned, complex 1 represents not only a rare example of homospin Fe(ii)-based SCMs but also the first Fe(ii) chain compound with pure EO-azido bridges.

Assembly of Imidazolyl-Substituted Nitronyl Nitroxides into Ferromagnetically Coupled Chains

New nitronyl nitroxides, namely, 2-(4,5-dimethylimidazol-2-yl)- and 2-(4,5-dichloroimidazol-2-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-3-oxide-1-oxyl, were prepared in crystalline form. According to single-crystal X-ray data, intra- and intermolecular hydrogen bonds are formed between NH groups of the imidazole cycles and O atoms of the nitroxide moieties. The intermolecular H-bonds contribute to the alignment of molecules into chains along the a-axis; this alignment causes short intrachain contacts between O and C atoms carrying spin density of opposite signs. Such an arrangement of nitroxides induces ferromagnetic intrachain interactions (J ≈ 10 cm−1) between neighboring radicals.

Coupling Influences SMM Properties for Pure 4 f Systems.

Increasing both the energy barrier for magnetization reversal and the coercive field of the hysteresis loop are significant challenges in the field of single-molecule magnets (SMMs). Coordination geometries of lanthanide ions and magnetic interactions between lanthanide ions are both important for guiding the magnetic behavior of SMMs. We report a high energy barrier of 657 K (457 cm-1 ) in a diamagnetic-ion-diluted lanthanide chain compound with a constrained bisphenoid symmetry (D2d ); this energy barrier is substantially higher than the barrier of 567 K (394 cm-1 ) of the non-diluted chain compound with intrachain ferromagnetic interactions. Although intrachain magnetic interaction lowers the energy barrier for magnetization reversal, it can greatly enhance the coercive fields and zero-field remanence of the hysteresis loops, which is crucial for the rational design of high-performance SMMs. Factors related to the coordination sphere of the lanthanide center, which govern the high magnetic relaxation barriers through the second excited Kramer's doublets and the magnetic interactions that affect the hysteresis loops, were revealed through ab initio calculations.

Solvent effects on the dimensionality of oxamato-bridged manganese(II) compounds

Two new oxamate-containing manganese(II) complexes, [{Mn(H2edpba)(H2O)2}2]n (1) and [Mn(H2edpba)(dmso)2]∙dmso∙CH3COCH3∙H2O (2) (H4edpba = N,N′-ethylenediphenylenebis(oxamic acid) and dmso = dimethylsulfoxide), have been synthesized and the structures of 1 and 2 were characterized by single crystal X-ray diffraction. The structure of 1 consists of neutral honeycomb networks in which each manganese(II) is six-coordinate by one H2edpba2− ligand and two carboxylate–oxygens from two other H2edpba2− ligands building the equatorial plane. Each manganese is connected to its nearest neighbor through two carboxylate(monoprotonated oxamate) bridges in an anti-syn conformation. A dmso solution of single crystals of 1 was placed under acetone atmosphere affording 2, whereas putting 2 in equimolar water:ethanol mixture results in 1. The molecular structure of 2 is made up of mononuclear manganese(II) units which are interlinked by weak C–H⋯π and edge-to-face π-stacking interactions leading to supramolecular chains along the crystallographic b axis. Magnetic measurements reveal the occurrence of an antiferromagnetic coupling between two manganese(II) ions through anti-syn carboxylate bridges for 1 [J = −1.18 cm−1, the Hamiltonian being defined as H = −J S1.S2] and very weak intrachain ferromagnetic interactions in 2 [J = + 0.046 cm−1, H = −J ∑iSi.Si + 1].

A Rare Water and Hydroxyl-Extended One-Dimensional Dysprosium(III) Chain and Its Magnetic Dilution Effect.

A novel water and hydroxyl-extended one-dimensional dysprosium(III) chain was hydrothermally obtained, which exhibits a relatively high spin-reversal energy barrier of 88.7 K and intrachain ferromagnetic interaction with the coupling constant Jexch = 3.04 cm-1 calculated by fitting magnetic susceptibilities using POLY_ANISO program based on ab initio calculations. To deeply understand the respective role of the single-ion anisotropy and intrachain exchange on the effective energy barrier, three crystallographically isostructural analogues containing isotropic Gd(III)-, diamagnetic Y(III)-, as well as Y(III)-doped Dy0.05Y0.95 were prepared and characterized structurally and magnetically. Due to the absence of significant intrachain exchange interaction, the effective energy barrier of the Dy0.05Y0.95 decreased by 9.9 K as compared with that of parent dysprosium(III) chain. Thus, it can be concluded that the intrachain ferromagnetic coupling and the magnetic anisotropy of the Dy(III) ion synergistically enhance the effective energy barrier of the dysprosium(III) chain, in which the single-ion anisotropy becomes more predominant.

Magnetic phase diagram of the organic antiferromagnet F4BImNN

We present a combination of heat capacity and ac susceptibility measurements as a function of temperature and field, of a single crystal of the radical 2-(4,5,6,7-tetrafluorobenzimidazol-2-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl. Our results confirm a zero-field Néel temperature at TN(0)=0.73K and allow the determination of the critical field parameters Hc(||)=170Oe and Hc(⊥)=306Oe. Assuming the previously determined 1-D intrachain ferromagnetic exchange interaction of Jintra/k=+22K between radicals, the interchain antiferromagnetic interaction is calculated as zJinter/k∼−0.03K.

Static and dynamic magnetic properties of the ferromagnetic coordination polymer [Co(NCS)2(py)2]n.

[Co(NCS)2(py)2]n (py = pyridine) is composed of ferromagnetic chains of Co(ii) cations connected by double NCS bridges. The chains are irregular because of two crystallographically inequivalent Co(ii) cations. The coordination polyhedron of the Co(ii) cations is a distorted octahedron built from two N and two S atoms of four equatorial NCS anions and two apical N atoms of the pyridine ligands. Magnetic and specific heat studies show that the compound undergoes a phase transition at 3.7 K to a ferromagnetic state. The determined magnetic interactions, intrachain (J/kB = 28 K) and interchain (zJ'/kB = 0.5 K), confirm the quasi 1D Ising magnetic character of [Co(NCS)2(py)2]n. Using AC magnetic susceptibility measurements the energy barriers for magnetization reversal of different relaxation processes were determined including those of the individual chains. By means of high field-high frequency ESR study the magnetic excitations were observed and explained in the frame of the Ising model in agreement with the results of the magnetic study. Ab initio calculations confirm the high magnetic anisotropy of the system and allow determination of the direction of the easy-axis. The broken symmetry DFT calculations support the ferromagnetic intrachain interactions. The energetic relations relevant for relaxations are discussed. It is concluded that the magnetic model of [Co(NCS)2(py)2]n is not a pure Ising but the transversal exchange plays a role.

Redox effects of low-spin Ru(ii/iii) on slow magnetic relaxation of Ru-Mn(iii) 1D cyanide-bridged complexes.

A new one-dimensional cyanide-bridged complex [MnIII(salphen)RuII(DMAP)4(CN)2](PF6) (1) and its oxidized derivative [MnIII(salphen)RuIII(DMAP)4(CN)2](PF6)2 (2) have been synthesized and fully characterized. Magnetic measurements showed that 1 shows simple paramagnetism but 2 shows intrachain ferromagnetic interaction with slow magnetic relaxation.

Effects of Metal Blending in Random Bimetallic Single-Chain Magnets: Synergetic, Antagonistic, or Innocent.

A family of isomorphous three-dimensional metal-organic frameworks based on bimetallic (FeCo, FeNi, and CoNi) chains with random metal sites have been prepared and magnetically characterized. The solid-solution-type bimetallic materials inherit intrachain ferromagnetic interactions and single-chain-magnet (SCM) behaviors from the homometallic parent materials. Interestingly, different composition dependence of magnetic behaviors has been found. The FeII1-x NiIIx series (0≤x≤1) show an innocent composition dependence, where the blocking temperature of slow relaxation decreases monotonically as FeII is replaced by less anisotropic NiII . The FeII1-x CoIIx series show an unexpected antagonistic blending effect on slow relaxation: blending FeII and CoII tends to depress the spin dynamics, and the bimetallic materials with intermediate composition show significantly lower blocking temperature than both FeII and CoII materials. This is quite the opposite of what happens in the Co1-x Nix series, where CoII and NiII seem to have a synergetic effect so that slow relaxation in bimetallic systems can be promoted to higher temperature than both CoII and NiII materials.

Spin Helicity in Chiral Lanthanide Chains.

We report here the determination of the helical spin structure of three Ln-based chiral chains of the formula [Ln(Hnic)(nic)2(NO3)]n (Hnic = nicotinic acid; Ln = Tb, Dy, and Er) by means of cantilever torque magnetometry. While the Dy and Er derivatives are strongly axial (easy-axis and easy-plane anisotropy, respectively), the Tb derivative is characterized by a remarkable rhombicity. In agreement with these findings, alternating-current susceptibility reveals slow magnetic relaxation only in the Dy derivative. Dilution of DyIII ions in the diamagnetic Y-based analogue shows that the weak ferromagnetic intrachain interactions do not contribute significantly to the energy barrier for the reversal of magnetization, which is better described as a single-ion process. Single crystals of the two enantiomers of the Dy derivative have also been investigated using hard X-ray synchrotron radiation at the L-edge of the metal revealing optical activity although with negligible involvement of the 4f electrons of the DyIII ion.