Strong Ferromagnetic Coupling Research Articles

Transition metal ion-directed magnetic behaviors observed in an isostructural heterobinuclear system

Four m-methylbenzoate (mb)-bridged heterometallic complexes, [DyM(H2O)(phen)(mb)5] (phen=1,10-phenanthroline, M=Ni (1), Fe (2), Cu (3), and Zn(4)), were solvothermally synthesized by varying different transition metal ions, and structurally and magnetically characterized. Structural analyses reveal that all the four samples are crystallographically isostructural, exhibiting triple carboxylate-bridged heterometallic binuclear structures with chelating phen molecule as terminus. Resulting from different magnetic nature of the transition metal ions, metamagnetic and weak antiferromagnetic interactions are respectively mediated between DyIII–NiII and DyIII–FeII ions by bidentate bridging carboxylate moiety. By contrast, strong ferromagnetic coupling is observed between DyIII–CuII. More interestingly, the former two complexes display field-induced single-molecule magnetic behavior with the anisotropy barriers of 20 and 17K, while 3 show frequency-dependent ac response by quantum tunneling. Thus, the combined dc and ac magnetic results from the simple binuclear model afford significant information for the heterometallic 3d–4f SMMs.

Radical Monocationic Guanidino-Functionalized Aromatic Compounds (GFAs) as Bridging Ligands in Dinuclear Metal Acetate Complexes: Synthesis, Electronic Structure, and Magnetic Coupling.

In this work, the oxidation of several new dinuclear metal (M) acetate complexes of the redox-active guanidino-functionalized aromatic compound (GFA) 1,2,4,5-tetrakis(tetramethylguanidino)benzene (1) was studied. The complexes [1{M(OAc)2}2] (M = Ni or Pd) were oxidized to the radical monocationic complexes [1{M(OAc)2}2](+ •). From CV (cyclic voltammetry) measurements, the Gibbs free enthalpy for disproportionation of [1{M(OAc)2}2](+ •) into [1{M(OAc)2}2] and [1{M(OAc)2}2](2+) could be estimated to be roughly +20 kJ mol(-1) in CH2Cl2 solution. A characteristic feature of the [1{M(OAc)2}2](+ •) complexes is the presence of intense metal-ligand charge-transfer bands in the electronic absorption spectra. The complex [1{Ni(OAc)2}2](+ •) combines three paramagnetic centers with four metal-centered unpaired electrons and a ligand centered π-radical and exhibits a sextet electronic ground state. Spin distribution of the Ni complexes was evaluated by paramagnetic (1)H and (13)C NMR and was correlated with calculations. The strong ferromagnetic metal-ligand magnetic coupling was studied in the solid state by magnetometric (SQUID) measurements and by quantum chemical (DFT) calculations. The temperature dependence of the paramagnetic NMR shift was used for the evaluation of the magnetic coupling between the Ni centers and the π-radical in solution.

Magnetization dynamics in ferromagnetic coupling interconnect wire using multiferroic logic scheme

Nowadays, the intense research effort is focused on exploring alternative emerging device to perform binary logical function. A promising device technology is multiferroic nanomagnet logic. The main reason for the interest in this nanomagnetic switch is its nonvolatility and comparatively low power consumption in combination with the ability to perform logic and storage in one single element. The basic element of multiferroic nanomagnet logic is a sub-100 nm size single domain magnet. Usually, the x-y direction defines the in-plane dimension, while the z axis direction depicts the thickness of nanomagnet. The in-plane magnetizations along easy axis are used to encode binary logic states 1 and 0, respectively; while along the hard axis they denote null logic. The logic operation and data transmission in magnetic logic are realized by the dipole-coupled magnetostatic interactions. In multiferroic nanomagnet logic, the interconnect wire is a very important component since it forms data transmission channel of any nanomagnetic logic circuit. There are two kinds of interconnected wires in this technology, namely antiferromagnetic coupling interconnected wire and ferromagnetic coupling interconnected wire. In this paper, the switching dynamics of a multiferroically and nanomagnetically interconnected wire employing ferromagnetic coupling is simulated by solving the Landau-Lifshitz-Gilbert equation with neglecting the thermal fluctuation effects. The wires are implemented with dipole-coupled two-phase (magnetostrictive/piezoelectric) multiferroic elements that are clocked with electrostatic potentials of 100 mV applied to the piezoelectric layer generating 20 MPa stress in the magnetostrictive layers for switching. Specifically, the ferromagnetic coupling effect model for multiferroic nanomagnet interconnected wire is established, and its magnetization dynamics is simulated by using different stress clocking. It is found that moderate strain (19.7-20.1 MPa) can ensure~180 magnetization reversal, and the logic state is successfully transferred in the ferromagnetic coupling interconnected wire. It is also found that the strong ferromagnetic coupling between multiferroic nanomagnets blocks effective magnetization reversal. This may arise from small spacing-induced out-of-plane magnetization, which does not favor the in-plane magnetization. These findings can provide some guidance for multiferroic logic circuit design.

Novel room-temperature spin-valve-like magnetoresistance in magnetically coupled nano-column Fe3O4/Ni heterostructure.

Herein, we design a room-temperature spin-valve-like magnetoresistance in a nano-column Fe3O4/Ni heterostructure without using a non-magnetic spacer or pinning layer. An Fe3O4 nano-column film is self-assembled on a Ni underlayer by the thermal decomposition method. The wet-chemical self-assembly is facile, economical and scalable. The magnetoresistance (MR) response of the Ni underlayer in the heterostructure under positive and negative out-of-plane magnetic fields differ by ∼0.25 at room temperature and ∼0.43 at 100 K. We attribute the spin-valve-like magnetoresistance to the unidirectional magnetic anisotropy of the Ni underlayer when being magnetically coupled by the Fe3O4 nano-column film. The out-of-plane negative-field magnetization is higher than the positive-field magnetization, affirming the unidirectional magnetic anisotropy of the Fe3O4/Ni heterostructure. Temperature-dependent magnetic and resistivity studies illustrate a close correlation between the magnetization transition of Fe3O4 and resistivity transition of Ni and prove a magnetic coupling between the Fe3O4 and Ni. First-principles calculations reveal that the Fe3O4/Ni model under a negative magnetic field is energetically more stable than that under a positive magnetic field. Furthermore, partial density of states (PDOS) analysis demonstrates the unidirectional magnetic anisotropy of the Ni 3d orbital. This is induced by the strong ferromagnetic coupling between Fe3O4 and Ni via oxygen-mediated Fe 3d-O 2p-Ni 3d hybridizations.

A unusual two-dimensional azido-Cu(ii) network with benzoate derivative as a co-ligand exhibiting ferromagnetic order and slow magnetic relaxation

A 2D layer-like Cu(ii) compound with multiple-bridges of azido, carboxylate and hydroxyl ligands, featuring strong ferromagnetic coupling and slow magnetic relaxation.

Ultrathin W space layer-enabled thermal stability enhancement in a perpendicular MgO/CoFeB/W/CoFeB/MgO recording frame.

Perpendicularly magnetized tunnel junctions (p-MTJs) show promise as reliable candidates for next-generation memory due to their outstanding features. However, several key challenges remain that affect CoFeB/MgO-based p-MTJ performance. One significant issue is the low thermal stability (Δ) due to the rapid perpendicular magnetic anisotropy (PMA) degradation during annealing at temperatures greater than 300 °C. Thus, the ability to provide thermally robust PMA characteristics is a key steps towards extending the use of these materials. Here, we examine the influence of a W spacer on double MgO/CoFeB/W/CoFeB/MgO frames as a generic alternative layer to ensure thermally-robust PMAs at temperatures up to 425 °C. The thickness-dependent magnetic features of the W layer were evaluated at various annealing temperatures to confirm the presence of strong ferromagnetic interlayer coupling at an optimized 0.55 nm W spacer thickness. Using this W layer we achieved a higher Δ of 78 for an approximately circular 20 nm diameter free layer device.

Size Effect on Interlayer Coupling and Magnetoresistance Oscillation of Magnetic Tunnel Junction Embedded With Iron Nanoparticles

Here, we investigate the size effect of perpendicular-anisotropic double-barrier magnetic tunnel junction (MTJ) devices embedded with iron nanoparticles. A sputtering system in conjunction with the postannealing process is employed to prepare the sheet film and standard lithography techniques followed by the ion etching technique are used to fabricate the micrometer to submicrometer MTJ devices. A strong ferromagnetic coupling is observed as we reduce the size of the device to submicrometer scale, which is due to the reduction of magnetostatic energy of the device. Furthermore, a magnetoresistance (MR) oscillation is observed at room temperature while reducing the size of the device. MR peaks at low bias fields are believed to have magnon contributions, whereas the peaks observed at higher bias fields are responsible for phonon-assisted tunneling. Zero-bias anomalies are also observed and are more prominent in antiparallel states of the devices.

Electron Hopping through Double-Exchange Coupling in a Mixed-Valence Diiminobenzoquinone-Bridged Fe2 Complex.

The ability of a benzoquinonoid bridging ligand to mediate double-exchange coupling in a mixed-valence Fe2 complex is demonstrated. Metalation of the bridging ligand 2,5-di(2,6-dimethylanilino)-3,6-dibromo-1,4-benzoquinone (LH2) with Fe(II) in the presence of the capping ligand tris((6-methyl-2-pyridyl)methyl)amine (Me3TPyA) affords the dinuclear complex [(Me3TPyA)2Fe(II)2(L)](2+). The dc magnetic measurements, in conjunction with X-ray diffraction and Mössbauer spectroscopy, reveal the presence of weak ferromagnetic superexchange coupling between Fe(II) centers through the diamagnetic bridging ligand to give an S = 4 ground state. The ac magnetic susceptibility measurements, collected in a small dc field, show this complex to behave as a single-molecule magnet with a relaxation barrier of U(eff) = 14(1) cm(-1). The slow magnetic relaxation in the Fe(II)2 complex can be switched off through one-electron oxidation to the mixed-valence congener [(Me3TPyA)2Fe2(L)](3+), where X-ray diffraction and Mössbauer spectroscopy indicate a metal-centered oxidation. The dc magnetic measurements show an S = 9/2 ground state for the mixed-valence complex, stemming from strong ferromagnetic exchange coupling that is best described considering electron hopping through a double-exchange coupling mechanism, with a double-exchange parameter of B = 69(4) cm(-1). In accordance with double-exchange, an intense feature is observed in the near-infrared region and is assigned as an intervalence charge-transfer band. The rate of intervalence electron hopping is comparable to that of the Mössbauer time scale, such that variable-temperature Mössbauer spectra reveal a thermally activated transition from a valence-trapped to detrapped state and provide an activation energy for electron hopping of 63(8) cm(-1). These results demonstrate the ability of quinonoid ligands to mediate electron hopping between high-spin metal centers, by providing the first example of an Fe complex that exhibits double-exchange through an organic bridging ligand and the largest metal-metal separation yet observed in any metal complex with double-exchange coupling.

Electronic and magnetic properties of Co2Fe(Ga1−xSix) and Co2Fe(Al1−ySiy) Heusler alloys with high Curie temperature

We investigate the electronic and magnetic properties of Co2Fe(Ga1−xSix) and Co2Fe(Al1−ySiy) alloys using first-principles density functional theory based method. With increasing concentration of Si, lattice constant decreases linearly whereas bulk modulus and total magnetic moment increase. Electronic structure calculations show that the minority DOS exhibits a gap around Fermi level confirming the half-metallic character of the material for all the concentrations studied and the Fermi level can be shifted within the energy gap by changing the Si concentration. The Heisenberg exchange coupling parameters obtained from our calculations predict strong ferromagnetic coupling and high Curie temperatures, which is in accord with the experimental results.

Long-range and strong ferromagnetic graphene by compensated n–p codoping and π–π stacking

Generating magnetism in graphene and preserving its extraordinary properties are essential to the development of graphene-based spintronics. By using first-principles calculation methods, we propose a new scheme based on compensated n–p codoping and non-covalent π–π stacking with F4-TCNQ, to engineer some hybrid structures of Fe/graphene/F4-TCNQ. Our results firstly show that F4-TCNQ adsorption on graphene can preserve the original electronic properties of graphene by minimizing the distortion of carbon–carbon lattices due to non-covalent π–π interaction between graphene and F4-TCNQ. Moreover, F4-TCNQ adsorption on graphene can lead it to p-type, which is in agreement with experimental finding. Then, n-type Fe adatom on F4-TCNQ/graphene system forms very stable hybrid Fe/graphene/F4-TCNQ system due to compensated n–p codoping interaction. Further calculations reveal that a long-range and strong ferromagnetic coupling of two Fe adatoms is realized by F4-TCNQ exchange interaction in the hybrid Fe/graphene/F4-TCNQ system. This study provides a new method to realize ferromagnetic graphene and preserve its extraordinary properties, which will open a promising way to tailor the electronic properties and magnetic properties of graphene so as to be suited for future application in nanoelectronics and spintronic devices.

Realization of multifunctional shape-memory ferromagnets in all-d-metal Heusler phases

Heusler ferromagnetic shape-memory alloys (FSMAs) normally consist of transition-group d-metals and main-group p-elements. Here, we report the realization of FSMAs in Heusler phases that completely consist of d metals. By introducing the d-metal Ti into NiMn alloys, cubic B2-type Heusler phase is obtained and the martensitic transformation temperature is decreased efficiently. Strong ferromagnetism is established by further doping Co atoms into the B2-type antiferromagnetic Ni-Mn-Ti austenite. Based on the magnetic-field-induced martensitic transformations, collective multifunctional properties are observed in Ni(Co)-Mn-Ti alloys. The d metals not only facilitate the formation of B2-type Heusler phases but also establish strong ferromagnetic coupling and offer the possibility to tune the martensitic transformation.

Strong ferromagnetically-coupled spin valve sensor devices for droplet magnetofluidics.

We report a magnetofluidic device with integrated strong ferromagnetically-coupled and hysteresis-free spin valve sensors for dynamic monitoring of ferrofluid droplets in microfluidics. The strong ferromagnetic coupling between the free layer and the pinned layer of spin valve sensors is achieved by reducing the spacer thickness, while the hysteresis of the free layer is eliminated by the interplay between shape anisotropy and the strength of coupling. The increased ferromagnetic coupling field up to the remarkable 70 Oe, which is five-times larger than conventional solutions, brings key advantages for dynamic sensing, e.g., a larger biasing field giving rise to larger detection signals, facilitating the operation of devices without saturation of the sensors. Studies on the fundamental effects of an external magnetic field on the evolution of the shape of droplets, as enabled by the non-visual monitoring capability of the device, provides crucial information for future development of a magnetofluidic device for multiplexed assays.

Interlayer exchange coupling between FeCo and Co ultrathin films through Rh(001) spacers

Using spin density functional theory (SDFT) calculations, we have studied the magnetic states, including collinear and noncollinear magnetic interlayer coupling, of ${\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}$ ultrathin films sandwiching Rh(001) layers. We found very large values for the interlayer exchange coupling (IEC) in $\mathrm{Co}/{\mathrm{Rh}}_{n}/\mathrm{Co}$ or ${(\mathrm{FeCo})}_{m}/{\mathrm{Rh}}_{n}/\mathrm{Co}$ structures as compared to, e.g., Ag or Au spacer layers. The IEC oscillates with the Rh spacer thickness showing a transition between strong antiferromagnetic and ferromagnetic coupling between five- and seven-layer thickness of the Rh film. Moreover, depending on the thickness of the FeCo film, a reorientation transition between in-plane and out-of-plane easy axis was found when spin-orbit coupling is considered in the calculations. This result suggests that, for specific arrangements such as ${(\mathrm{FeCo})}_{2}/{\mathrm{Rh}}_{5}/\mathrm{Co}$ structures, a competition between IEC and magnetic anisotropy of coupled films may result in noncollinear ordering. This possibility was studied with constrained, noncollinear SDFT calculations and the results were mapped onto a classical spin model to explore the richness of spin structures that can arise in these multilayer systems.

Multifunctional one-dimensional rhodium(I)-semiquinonato complex: substituent effects on crystal structures and solid-state properties.

Two new one-dimensional (1D) rhodium(I)-semiquinonato complexes formulated as [Rh(3,6-DBSQ-4,5-PDO)(CO)2]∞ (4; 3,6-DBSQ-4,5-PDO(•-) = 3,6-di-tert-butyl-4,5-(1,3-propanedioxy)-1,2-benzosemiquinonato) and [Rh(3,6-DBSQ-4,5-(N,N'-DEN))(CO)2]∞ (5; 3,6-DBSQ-4,5-(N,N'-DEN)(•-) = 3,6-di-tert-butyl-4,5-(N,N'-diethylenediamine)-1,2-benzosemiquinonato) were synthesized to explore the nature of the unusual structural phase transition and magnetic and conductive properties recently reported for [Rh(3,6-DBSQ-4,5-(MeO)2)(CO)2]∞ (3; 3,6-DBSQ-4,5-(MeO)2(•-) = 3,6-di-tert-butyl-4,5-dimethoxy-1,2-benzosemiquinonato). Their crystal structures and magnetic and conductive properties were investigated. Compounds 4 and 5 comprise neutral 1D chains of complex molecules stacked in a staggered arrangement with fairly short average Rh-Rh distances of 3.06 Å for 4 and 3.10 Å for 5. These distances are similar to those for 3 (3.09 Å); however, the molecules of 5 are strongly dimerized in the 1D chain. Compound 4 undergoes a first-order phase transition at Ttrs = 229.1 K, and its magnetic properties drastically change from antiferromagnetic coupling in the room-temperature (RT) phase to strong ferromagnetic coupling in the low-temperature (LT) phase. In addition, compound 4 exhibits a long-range ordering of net magnetic moments originating from the imperfect cancellation of antiferromagnetically coupled spins between the ferromagnetic 1D chains at TN = 10.9 K. Furthermore, this compound exhibits an interesting crossover from a semiconductor with a small activation energy (Ea = 31 meV) in the RT phase to a semiconductor with a large activation energy (Ea = 199 meV) in the LT phase. These behaviors are commonly observed for 3. Alternating current susceptibility measurements of 4, however, revealed a frequency-dependent phenomenon below 5.2 K, which was not observed for 3, thus indicating a slow spin relaxation process that possibly arises from the movements of domain walls. In contrast, compound 5, which possesses a strongly dimerized structure in its 1D chain, shows no sign of strong ferromagnetic interactions and is an insulator, with a resistivity greater than 7 × 10(7) Ω cm.

A variational theory of zero field electrical resistivity of colossal magnetoresistive manganites (Re1-xAxMnO3)

Using a simple variational method, we have studied the zero field electrical resistivity ρ(T) of rare earth manganites doped with alkaline earths namely Re1-xAxMnO3which exhibit colossal magnetoresistance (CMR), metal–insulator transition and many other poorly understood phenomena. We take the two band model Hamiltonian for manganites in the strong electron-lattice Jahn–Teller (JT) coupling regime. This model is constructed for the doped manganites which exhibit colossal magnetoresistance (CMR) involving a broad spin-majority (eg-spins) conduction band (b-band) as well as nearly localized spin-minority (t2g-spins) electron states (ℓ-band). Two band models involving itinerant and localized states were also suggested earlier by both experimentalists and theorists. We have also studied the temperature dependence of electrical resistivity ρ(T) at H = 0 of these materials and observed the role of the model parameters e.g. local Coulomb repulsion U, strong ferromagnetic Hund's rule coupling JHbetween egand t2gspins and hybridization V between ℓ-polarons and b-electrons of the same spins on ρ(T). We find from the resistivity results that as the temperature is lowered below a critical temperature Tc(~ 200 K), there is a sudden drop in electrical resistivity ρ(T) at H = 0 resembling with the key feature of many CMR compounds like La2/3( Pb , Ca )1/3MnO3and ( Sm1-yGdy)0.55Sr0.45MnO3at y = 0.5. This anomaly in ρ(T) arises from the onset of magnetic ordering at 200 K and vanishes on increasing V or JHvalue. T-dependence of ρ(T) is metallic-like below Tc(~ 200 K), above which it shows insulator/semiconducting-like behavior.

A comparative study on magnetism in Zn-doped AlN and GaN from first-principles

First-principles calculations have been used to comparatively investigate electronic and magnetic properties of Zn-doped AlN and GaN. A total magnetic moment of 1.0 μB induced by Zn is found in AlN, but not in GaN. Analyses show that the origin of spontaneous polarization not only depend on the localized atomic orbitals of N and sufficient hole concentration, but also the relative intensity of the covalency of matrix. The relatively stronger covalent character of GaN with respect to AlN impedes forming local magnetic moment in GaN matrix. Our study offers a fresh sight of spontaneous spin polarization in d0 magnetism. The much stronger ferromagnetic coupling in c-plane of AlN means that it is feasible to realize long-range ferromagnetic order via monolayer delta-doping. This can apply to other wide band-gap semiconductors in wurtzite structure.

Electronic and magnetic structure of neutral radical FBBO

The fluorinated oxobenzo-bridged bisdithiazolyl radical FBBO was recently observed to undergo a pressure-induced Mott insulator-to-metal transition, suggesting a novel organic system for studying Mott physics. This report describes the electronic structure of this material in relation to the observed magnetic response at low pressures. Through analysis of antiferromagnetic resonance measurements, we identify a layered antiferromagnetic ordered phase below ${T}_{N}=13$ K at ambient pressure, which requires strong ferromagnetic coupling between nearest neighbours. The origin of such coupling is elucidated from both molecular and solid-state electronic-structure calculations, which suggest a minimal two-orbital model with strong Hund's-rule coupling. This layered phase is partially frustrated by a second-nearest-neighbor antiferromagnetic coupling, which drives a magnetic phase transition at elevated pressure. On the basis of the two-orbital model, we suggest the pressure-induced Mott transition to proceed via rehybridization of the frontier molecular orbitals, resulting in a half-filled insulator to quarter-filled metal crossover.

Hysteresis-free spin valves with a noncollinear configuration of magnetic anisotropy

A noncollinear configuration of magnetic anisotropy in spin valves with strong and weak interlayer couplings has been formed by annealing and cooling in a magnetic field. The dependence of the lowfield magnetoresistance hysteresis loop width on the angle between the applied magnetic field and the principal axes of the magnetic anisotropy in a spin valve has been investigated. It has been found that, only in the case of a strong ferromagnetic interlayer coupling, the formation of a noncollinear configuration of the magnetic anisotropy provides a hysteresisfree character of the magnetization reversal of the free layer with retaining the maximum magnetoresistance and magnetoresistive sensitivity.

Effect of 3d transition elements substitution for Ni in Ni2Mn1+xSn1-x on the phase stability and magnetic properties: A first principle investigation

In hope of understanding the origin of the 3d-transition elements doping effect on the phase stability and magnetic properties of the ferromagnetic shape memory Heusler alloy Ni–Mn–Sn, the Ni–Z–Mn–Sn system with Z=Ni, Cu, Co, Fe, Mn and Cr is investigated using first-principles calculations. The calculated results show that the energetically favorable magnetic order of the L21 structure is antiferromagnetic for Z=Ni and Cu, and ferromagnetic for the Z=Co, Fe, Mn and Cr. However, for L10 structure, the antiferromagnetic state has an energetical preference for each alloy. Accordingly, a magnetic transition accompanies with the martensite phase transformation and a large change in the magnetic moment can be observed in the alloys with the L21 under the ferromagnetic state, which is mainly dependent on the coupling behaviors of the doped atoms. The weak ferromagnetic coupling between the Ni/Cu and Mn, the strong ferromagnetic coupling between Co/Fe and Mn and the antiferromagnetic coupling between Mn/Cr and Mn play an important role on the magnetic order of L21 structures. Furthermore, the Bethe–Slater model is employed to gain a further understanding and regulation of the coupling behaviors of different doping elements, which is very sensitive to the interatomic distance. These calculated results may help in gaining an insight into the doping behavior of these transition metals and provide some theoretical aid to the material design.

An unprecedented coordination mode of isonicotinate ligand in novel copper(II) polymeric complex: synthesis, spectral, thermal and magnetic properties and their comparison with known molecular analog

Two copper(II) isonicotinate complexes, [Cu(INA)2(H2O)4] (1) and {[Cu(INA-N-H)2(μ2-H2O)2]·2H2O·2NO3}n (2) were prepared using a one-pot synthesis and characterized by single-crystal X-ray diffraction, spectral and thermal analysis and magnetic susceptibility. Complex 1 provides Cu–N(pyridyl) coordination mode with ionic carboxylate functionality. A novel complex 2 exhibits a chain-like crystal structure in which the [Cu(INA-N-H)]2+ ions are bridged by μ2-H2O molecules. The structural, spectral and thermal correlations indicate significant influence of ligand coordination mode and non-covalent interactions to mentioned properties. Magnetic susceptibility data were fitted by Curie–Weiss law with Tc=0.68K for complex 1 and Tc=9.01K for complex 2. Magnetic studies show a very weak interaction between copper(II) centers within the network structure in complex 1 and stronger ferromagnetic coupling between Cu ions caused by the presence of intra-chain Cu–O–Cu interaction in complex 2.