Significant Magnetic Entropy Change Research Articles

Metamagnetic phase transition and corresponding magnetocaloric effect in intermetallic Ho1-xTbxCo2 alloys

A comprehensive investigation was conducted to examine the magnetic properties and magnetocaloric effect (MCE) around the phase transition temperature of the intermetallic Ho1-xTbxCo2 (x=0.05, 0.1, and 0.15) alloys. X-ray diffraction (XRD) investigations reveal that the single-phase alloys crystallize in the cubic phase (space group Fd3̅m) at room temperature and undergo a structural transition to the tetragonal phase (space group I41/amd) below their Curie temperatures. These alloys demonstrated a metamagnetic transition around their respective phase transition temperatures, accompanied by a remarkable MCE and negligible hysteresis loss. The Landau free energy study confirmed the existence of the first-order magnetic transition in the aforementioned samples. The spin reorientation occurring below the transition temperature was observed. The studied alloys displayed significant magnetic entropy change (ΔSM) values of 15.6 JKg−1K−1, 15.2 JKg−1K−1, and 13.06 JKg−1K−1 in a wide temperature span over 20 K under a magnetic field change (ΔH) of 5 T for x=0.05, 0.1, and 0.15, respectively. Furthermore, large refrigerant capacities (RC) of 323.6 Jkg−1, 311.28 Jkg−1, and 323.46 Jkg−1 were achieved under ΔH=5 T for these alloys. An unexpected asymmetric broadening of the ΔSM peak was observed as the magnetic field increased. A significant change in the adiabatic temperature (ΔTad) of 5.3–6 K was achieved under ΔH=5 T. The outstanding magnetocaloric performance of studied materials may make them promising for magnetic refrigeration applications within the 87–105 K temperature range.

Implementation of Backpropagation Neural Network for Prediction Magnetocaloric Effect of Manganite

In the field of magnetic cooling technology, there is still much to learn about the magnetocaloric properties of magnetic cooling materials. Research into magnetocaloric manganites exhibiting a significant maximum magnetic entropy change in the vicinity of ambient temperature yields encouraging outcomes for the advancement of magnetic refrigeration apparatus. Through a combination of chemical substitutions, changes in the amount of oxygen present, and different synthesis techniques, these manganites undergo lattice distortions that result in pseudocubic, orthorhombic, and rhombohedral structures instead of perovskite cubic structures. The present investigation used backpropagation neural networks (BPNNs) to investigate the correlations among maximum magnetic entropy change (MMEC), Curie temperature (Tc), lanthanum manganite compositions, lattice properties, and dopant ionic radii. Simbrain 3.07 was used to execute the BPNN model, and the suggested model accuracy was examined using coefficient determination. As a result, the model's predicted values for the mean absolute error, root mean square, and coefficient correlation for MMEC are 0.012, 0.022, and 0.9861, respectively. The model predicts that the Curie temperature mean absolute error, root mean square, and coefficient correlation will be 0.015, 0.021, and 0.9947, respectively. Based on these results, BPNN has the potential to be applied in predicting the MMEC and Tc of manganite as preliminary decision during experiments.

3d Ion-Driven Hexanuclear Heterometallic Clusters with Amazing Structures and Magnetic Properties

By using a heptadentate Schiff base ligand with three NO2 pockets to react with 3d and 4f acetate precursors, three series of M4Ln2 complexes (M, Ln = Ni, Gd for 1NiGd; Ni, Dy for 2NiDy; Co, Gd for 3CoGd; Co, Dy for 4CoDy; Cu, Gd for 5CuGd; Cu, Dy for 6CuDy) have been obtained and characterized. X-ray single-crystal diffraction analyses indicated that Ni4Ln2 series exhibit butterfly structures with extended wings, the Co4Ln2 series are made up of four fused linear defective open cubes, and the Cu4Ln2 series display H-typed topology structures. The dc magnetic susceptibility data revealed that all of the Gd derivatives possess significant magnetic entropy change, whereas the alternating current (ac) magnetic susceptibility measurements identified that only the NiDy derivative displays single-molecule magnet behavior with energy barrier of 15.69 K under zero dc field. These results reveal that 3d ions are important in adjusting the structure and magnetic properties for 3d–4f complexes.

Effect of annealing on microstructure and magnetocaloric properties of plastically deformed La0.7Ce0.3Fe13.68Mn0.2Si1.4 alloys

In this study, we have employed a near-net-shape hot forging deformation with ∼67% reduction ratio, and an annealing process at 1223–1423 K to prepare bulk La0.7Ce0.3Fe13.68Mn0.2Si1.4 alloys. The deformed samples are featured by a unique microstructure consisting of layered α-Fe and La-rich phases. These layered phases gradually degrade during the subsequent annealing, and eventually appear as the magnetocaloric phase (the 1:13 phase) matrix embedded mainly with the α-Fe particles. Upon annealing at 1323 K, the deformed sample has the largest 1:13 phase formation rate. Significant magnetic entropy change of 15.6 J/kg K and a relatively small magnetic hysteresis of 30.9 J/kg at 5 T are achieved in the current forged La-Ce-Fe-Mn-Si alloy on an optimal annealing condition, i.e., 1323 K for 24 h. The large magnetic entropy, rapid 1:13 phase formation rate and near-net shape make the hot-forged La-Ce-Fe-Mn-Si alloys promising magnetic refrigerants.

Enhanced magnetocaloric properties of La0.8K0.2-xPbxMnO3 nanoparticles by optimizing Pb doping concentrations

Polycrystalline La0.8K0.2-xPbxMnO3 (x = 0.05, 0.10, 0.15, 0.20) ceramics were successfully prepared by flash combustion route and their structural, morphological, magnetic and magnetocaloric properties were investigated. Structural analyses using X-ray diffraction reveal that all samples are crystallized in the rhombohedral structure and belong to R3‾c space group. The increase of Pb doping does not modify the crystalline structure but changes the grain size and lattice parameters. X-ray photoelectron spectroscopy (XPS) fitting results of Mn 2p peaks confirmed the coexistence of Mn3+ and Mn4+ ions which contribute to the double exchange interactions improving the ferromagnetic order in the samples. The magnetization's temperature and magnetic field dependences indicate a second-order ferromagnetic-paramagnetic transition of the ceramics. A significant magnetic entropy change near room temperature was observed for La0.8K0.1Pb0.1MnO3,showing considerable magnetocaloric properties. Furthermore, electron paramagnetic resonance spectroscopy (EPR) was also used to examine the ferromagnetic-paramagnetic transition.

Study on the Magnetocaloric Effect of Room Temperature Magnetic Refrigerant Material La0.5Pr0.5(Fe1-xCox)11.4Si1.6 and the Effect Arising from Co Doping on Its Curie Temperature.

The arc-melting method was adopted to prepare the compound La0.5Pr0.5(Fe1−xCox)11.4Si1.6 (x = 0, 0.02, 0.04, 0.06, 0.08), and the magnetocaloric effect of the compound was investigated. As indicated by the powder X-ray diffraction (XRD) results, after receiving 7-day high temperature annealing at 1373 K, all the compounds formed a single-phase cubic NaZn13 crystal structure. As indicated by the magnetic measurement, the most significant magnetic entropy change |∆SM(T)| of the sample decreased from 28.92 J/kg·K to 4.22 J/kg·K with the increase of the Co content under the 0–1.5 T magnetic field, while the Curie temperature TC increased from 185 K to the room temperature 296 K, which indicated that this series of alloys are the room temperature magnetic refrigerant material with practical value. By using the ferromagnetic Curie temperature theory and analyzing the effect of Co doping on the exchange integral of these alloys, the mechanism that the Curie temperature of La0.5Pr0.5(Fe1−xCox)11.4Si1.6 and La0.8Ce0.2(Fe1−xCox)11.4Si1.6 increased with the increase in the Co content was reasonably explained. Accordingly, this paper can provide a theoretical reference for subsequent studies.

Two dinuclear GdIII clusters based on isobutyric acid and nicotinic acid with large magnetocaloric effects

Two dinuclear GdIII cluster complexes with the formulas [Gd2(iba)6(bipy)2] (1) and [Gd2(nic)6(H2O)4] (2) (Hiba = isobutyric acid, Hnic = nicotinic acid and bipy = 2,2´-bipyridine) have been constructed by using gadolinium oxide as GdIII ion source under hydrothermal conditions. Although both 1 and 2 exhibit dinuclear structures, the coordination fashions are totally different. In 1, the carboxylate groups of Hiba take syn-syn-μ2-η1:η1, syn-syn-μ2-η1:η2 and syn-μ-η1:η1 modes and bipy acts as the chelating ligand. While the carboxylate groups of Hnic display syn-syn-μ2-η1:η1 and syn-μ-η1:η1 modes in 2 and two water molecules take part in coordination. Magnetic studies reveal weak ferromagnetic couplings and significant magnetic entropy changes with −ΔSmmax = 29.3 J kg−1 K−1 and 27.4 J kg−1 K−1 (ΔH = 7 T), respectively.

Multicaloric effect in multiferroic sulpho spinel MCr2S4 (M = Fe & Co)

We observe a rare occurrence of multiple caloric effects in multiferroic FeCr2S4 & CoCr2S4 compounds having a spinel structure. The significant magnetic entropy changes of ∼3.72 J kg-1 K−1 and 3.99 J kg−1 K−1 are observed in FeCr2S4 & CoCr2S4, respectively, for a magnetic field change of 0–50 kOe at the paramagnetic to ferrimagnetic transition (TN). At TN large magnetoresistances are also observed as ∼17% and ∼10.2% for FeCr2S4 & CoCr2S4, respectively, for applied magnetic field 50 kOe. On the other hand, the electrocaloric entropy are also found considerable as ∼0.56 J-m−3 K−1 and 1.24 J-m−3 K−1 for a small electric field change of 0–100 kV/m at the ferroelectric transition temperature (TC) for CoCr2S4 & FeCr2S4, respectively.

Two Gd2 cluster complexes with monocarboxylate ligands displaying significant magnetic entropy changes

Two Gd2 cluster complexes with the formulas of [Gd2(dnba)6(phen)2] (1) and [Gd2(Hnsa)2(nsa)2(phen)2(H2O)2] (2) (Hdnba = 3,5-dinitrobenzoic acid, H2nsa = 5-nitrosalicylic acid and phen = 1,10-phenanthroline) respectively have been successfully synthesized under hydrothermal conditions. The GdIII ions of 1 are bridged by four carboxylates with syn-syn-μ2-η1:η1 and syn-syn-μ2-η1:η2 modes, while the GdIII ions of 2 are linked by two carboxylate ligands with only syn-syn-μ2-η1:η2 mode. Magnetic studies indicate that weak antiferromagnetic and ferromagnetic interactions exist between the adjacent GdIII ions within Gd2 clusters, respectively. Complexes 1 and 2 display distinct magnetocaloric effects induced by different magnetic interactions and magnetic densities. Notably, the maximum magnetic entropy changes (−ΔSmmax) of 1 and 2 reach 16.8 J kg−1 K−1 and 22.2 J kg−1 K−1 with ΔH = 7 T at 2 K and 3.5 K, respectively.

High temperature spin reorientation, magnetization reversal and magnetocaloric effect in 50% Mn substituted polycrystalline ErFeO3

The structural, magnetic and magnetocaloric properties of 50% Mn substituted ErFeO3 are studied by X-ray diffraction, magnetization and specific heat measurements. ErFe0.5Mn0.5O3 crystallizes in an orthorhombic structure (Pbnm). DC magnetization and specific heat studies point to two magnetic transitions: (i) Fe3+/Mn3+ ordering, TN ~ 245 K and (ii) spin re-orientation transition, TSR ~ 218 K. Below TSR, ErFe0.5Mn0.5O3 exhibits a reduction in magnetization and coercivity which could be due to a Γ4-Γ1 magnetic transition. Interestingly, we have observed a negative magnetization in field cooled curves at lower temperatures under lower applied fields (<50 Oe) as a result of the polarization of paramagnetic Er3+ moments with the internal field created by Mn3+ ordering from the Mn-rich regions. A significant magnetic entropy change (-ΔSm) of 13.4 J/kg.K is also observed at 9.5 K for an applied field of 7 T.

Evidence of large magnetic cooling power and double glass transition in Tb5Pd2

We report a detailed dc magnetization, ac susceptibility and magnetocaloric properties of a binary intermetallic compound Tb5Pd2. Our dc magnetization and heat capacity results reveal the absence of long range ordering in this compound. Two distinct frequency dependent peaks (Tf1∼60 K and Tf2∼21 K) had been observed in the ac-susceptibility. Analysis of these frequency dependent peaks by Mydosh parameter, power and Vogel-Fulcher law reveals that around Tf1 the compound is at the boundary of spin glass (SG) like-cluster glass (CG) like state and it undergoes a cluster glass-like freezing below Tf2. Zero field cooled memory effect and non-linear dc susceptibility also confirmed the presence of two glassy transitions in this compound. The transformation from SG/CG boundary to CG phase was also confirmed by the magnetic relaxation measurement and Arrott plots study. Remarkably, a significant magnetic entropy change was also observed in the temperature range of 60–120 K. Additionally a large relative cooling power also observed in this compound. The observed value is comparable to those of promising refrigerant material in this temperature range and is quite notable as in this compound magnetic hysteresis was absent in this temperature range. It was noted that in this compound short-range interactions persist up to a higher temperature above Tf1 and this is responsible for the observation of significant MCE over a wide temperature range. Our studies suggest that this compound is an example of a glassy magnetic compound which shows large magnetocaloric effect.

Magnetocaloric effect in Fe-based amorphous alloys and their composites with low boron content

The amorphous soft magnetic Fe88Zr11B1 ribbon was fabricated and the magnetocaloric effect of it was investigated through the measurement of magnetization in this work. To enhance its magnetocaloric effect, Co is selected as a microalloying addition to this precursor. Among these ribbons, the replacement of Fe by minor Co, compared with the replacement of Zr by Co, gives more increment in Curie temperature and magnetic entropy change. Fe86Zr11B1Co2 exhibits the largest peak value of magnetic entropy change of 1.73 Jkg−1 K−1 and Fe88Zr9B1Co2 shows the largest refrigerant capacity of 149.7 Jkg−1 for an applied field of 15 kOe. Furthermore, a significant magnetic entropy change can be obtained using multiphase materials in this work. Under a magnetic field change of 15 kOe, the maximum improvement of the refrigerant capacity by 38.6%, in comparison with those of the individual alloys, is obtained for the layered composite of Fe88Zr11B1 (50 wt%) and Fe86Zr11B1Co2 (50 wt%). Besides, a quite broad SM(T) curve around room temperature of the amorphous composite is observed, which is a key feature for an Ericsson magnetic refrigeration cycle.

Table-like magnetocaloric effect and large refrigerant capacity in Gd65Mn25Si10-Gd composite materials for near room temperature refrigeration

Amorphous Gd65Mn25Si10 as well as crystalline Gd have technologically significant Curie temperature and large magnetic entropy change. Two types of composite materials Gd65Mn25Si10-Gd were fabricated: laminating Gd sheets and amorphous Gd65Mn25Si10 ribbons (multilayer composite) and hot pressing a mixture of amorphous Gd65Mn25Si10 thin ribbons, Gd particles and a small amount of Sn powders (bulk composite). A table-like magnetocaloric effect (MCE) in a wide, commercially useful, temperature span of 73 K (220 K-293 K) were observed in these composites. The values of full-width at half maximum of (−ΔSM) − T plots (ΔTFWHM) and enhanced refrigerant capacity (RC) for the multilayer and bulk composites are 212 K, 724 J/kg, and 248 K, 617 J/kg, respectively, for a field of 5 T. Large ΔTFWHM and RC values and the table-like (−ΔSM)max feature suggest that both multilayer and bulk Gd65Mn25Si10-Gd composites can meet the requirements of different magnetic refrigeration based on Ericsson-cycle.

Channel-Assisted Proton Conduction Behavior in Hydroxyl-Rich Lanthanide-Based Magnetic Metal-Organic Frameworks.

Two new lanthanide-based 3D metal-organic frameworks (MOFs), {[Ln(L)(Ox)(H2O)]n·xH2O} [Ln = Gd3+ and x = 3 (1) and Dy3+ and x = 1.5 (2); H2L = mucic acid; OxH2 = oxalic acid] showing interesting magnetic properties and channel-mediated proton conduction behavior, are presented here. Single-crystal X-ray structure analysis shows that, in complex 1, the overall structure originates from the mucate-bridged gadolinium-based rectangular metallocycles. The packing view reveals the presence the two types of hydrophilic 1D channels filled with lattice water molecules, which are strongly hydrogen-bonded with coordinated water along the a and b axes, whereas for complex 2, the 3D framework originates from a carboxylate-bridged dysprosium-based criss-cross-type secondary building block. Magnetic studies reveal that 1 exhibits a significant magnetic entropy change (-ΔSM) of 30.6 J kg-1 K-1 for ΔH= 7 T at 3 K. Our electronic structure calculations under the framework of density functional theory reveal that exchange interactions between Gd3+ ions are weak and of the antiferromagnetic type. Complex 2 shows field-induced single-molecule-magnetic behavior. Impedance analysis shows that the proton conductivity of both complexes reaches up to the maximum value of 4.7 × 10-4 S cm-1 for 1 and 9.06 × 10-5 S cm-1 for 2 at high temperature (>75 °C) and relative humidity (RH; 95%). The Monte Carlo simulations confirm the exact location of the adsorbed water molecules in the framework after humidification (RH = 95%) for 1. Further, the results from computational simulation also reveal that the presence of a more dense arrangement of adsorbed water molecules through hydrogen bonding in a particular type of channel (along the a axis) contributes more to the proton migration compared to the other channel (along the b axis) in the framework.

Pentanuclear Lanthanide Mono-organophosphates: Synthesis, Structure, and Magnetism.

Research on rare-earth phosphates has recently received substantial interest because of their unique physical and chemical properties. In recent years, because of their low solubility, research interest has been built on developing methodologies to prepare nanostructures and grow single crystals of inorganic rare-earth phosphates. The chemistry of rare-earth organophosphates, however, is still at a latent stage. Contrary to the traditional hydrothermal route, we report rare examples of discrete pentanuclear lanthanide(III) organophosphate clusters assembled from a sterically encumbered monoester of phosphoric acid under mild reaction conditions. Single-crystal X-ray analysis revealed that all of the compounds possess a similar core structure, [Ln5(μ3-OH)(dipp)6(NO3)x(CH3OH)y(H2O)z]2+ [Ln = Nd (1), Sm (2), Eu (3), Gd (4), Tb (5), Dy (6), Ho (7), Er (8), Tm (9); dipp = 2,6-diisopropylphenylphosphate], where the anionic charge balance is maintained by the presence of chelating nitrate anions (in the case of 9, x = 0), protonated tmeda, or dipp2- ligands. The vacant coordination sites on the metal ions are satisfied by coordinated methanol or water molecules. The core structure of these clusters is built on a [Ln3(μ3-OH)(dipp)6] triangle where the phosphate ligands bridge to two further Ln(III) ions. The complexes display lanthanide contraction along the series, with Ln(III) ions displaying different coordination environments/geometries as we move along the series. All of the compounds have been characterized by both analytical and spectroscopic techniques. Magnetic studies revealed the presence of weak antiferromagnetic exchange through the bridging μ3-hydroxo moiety and organophosphate groups for the {GdIII5} analogue, with a significant magnetic entropy change (25.8 J kg-1 K-1, ΔH = 7 T). The anisotropic complexes reveal an absence of slow relaxation of magnetization, except for Nd (1), Dy (6), and Er (8), which show slow relaxation in an applied DC field.

Modulating Magnetic Refrigeration through Structural Variation in CoII/III-GdIII Clusters.

Three heterometallic aggregates, [(CoII)2(GdIII)2(tBuPO3)2(O2CtBu)2(HO2CtBu)2(NO3)4]·NEt3 (1), [(CoII)2(CoIII)2(GdIII)3(μ3-OH)2(tBuPO3)2(O2CtBu)9(deaH)2(H2O)2] (2), and (CoIII)2(GdIII)5(μ2-OH)(μ3-OH)2(tBuPO3)2(O2CtBu)10(HO2CtBu)(deaH)2]·MeOH (3), were successfully isolated in reactions of [Co2(μ-OH2)(O2CtBu)4]·(HO2CtBu)4, Gd(NO3)3·6H2O, tBu-PO3H2, and diethanolamine (deaH3) by varying the stoichiometry of the reactants and/or changing the solvent. The structures of the final products were profoundly affected by these minor changes in stoichiometry or a change in solvent. The metal-oxo core of these complexes displays a hemicubane or a defective dicubane-like view. Bond valence sum calculations and bond lengths indicate the presence of CoII centers in compound 1, mixed valent Co centers (CoII/CoIII) in compound 2, and only CoIII centers in compound 3 as required for the charge balances and supported by the magnetic measurements. Magnetic studies reveal significant magnetic entropy changes for complexes 1-3 (-ΔSm values of 28.14, 25.06, and 29.19 J kg-1 K-1 for 3 K and 7 T, respectively). This study shows how magnetic refrigeration can be affected by anisotropy, magnetic interactions (ferro- or antiferromagnetic), the metal/ligand ratio, and the content of GdIII in the molecule.

Two di- and trinuclear Gd(III) clusters derived from monocarboxylates exhibiting significant magnetic entropy changes

Two di- and trinuclear Gd(III) clusters with the formulas {[Gd2(omba)6(phen)2]·2H2O} (1) and [Gd3(Hsa)5(sa)2(phen)3] (2) (Homba=o-methoxybenzoic acid, H2sa=salicylic acid and phen=1,10-phenanthroline) have been prepared through the hydrothermal reactions. Complex 1 takes a dinuclear structure and two Gd(III) are bridged by two syn-syn-μ2-η1:η1 and two syn-syn-μ2-η1:η2 carboxylates. While complex 2 is a trinuclear cluster linked by one syn-syn-μ2-η1:η2 and two syn-syn-μ2-η1:η1 carboxylates. Magnetic studies reveal the key impact of magnetic density on the magnetocaloric effect in Gd(III) systems. They exhibit relatively weak magnetic interactions and significant magnetic entropy changes with −ΔSmmax=17.1Jkg−1K−1 and 22.5Jkg−1K−1 (T=2K, ΔH=7T), respectively.

Proton-Conducting Magnetic Coordination Polymers.

Three isostructural lanthanide-based two- dimensional coordination polymers (CPs) {[Ln2(L)3(H2O)2]n⋅2n CH3OH)⋅2n H2O} (Ln=Gd(3+) (1), Tb(3+) (2), Dy(3+) (3); H2L=cyclobutane-1,1-dicarboxylic acid) were synthesized by using a low molecular weight dicarboxylate ligand and characterized. Single-crystal structure analysis showed that in complexes 1-3 lanthanide centers are connected by μ3-bridging cyclobutanedicarboxylate ligands along the c axis to form a rod-shaped infinite 1D coordination chain, which is further linked with nearby chains by μ4-connected cyclobutanedicarboxylate ligands to form 2D CPs in the bc plane. Viewing the packing of the complexes down the b axis reveals that the lattice methanol molecules are located in the interlayer space between the adjacent 2D layers and form H-bonds with lattice and coordinated water molecules to form 1D chains. Magnetic properties of complexes 1-3 were thoroughly investigated. Complex 1 exhibits dominant ferromagnetic interaction between two nearby gadolinium centers and also acts as a cryogenic magnetic refrigerant having a significant magnetic entropy change of -ΔSm=32.8 J kg(-1) K(-1) for ΔH=7 T at 4 K (calculated from isothermal magnetization data). Complex 3 shows slow relaxation of magnetization below 10 K. Impedance analysis revealed that the complexes show humidity-dependent proton conductivity (σ=1.5×10(-5) S cm(-1) for 1, σ=2.07×10(-4) S cm(-1) for 2, and σ=1.1×10(-3) S cm(-1) for 3) at elevated temperature (>75 °C). They retain the conductivity for up to 10 h at high temperature and high humidity. Furthermore, the proton conductivity results were correlated with the number of water molecules from the water-vapor adsorption measurements. Water-vapor adsorption studies showed hysteretic and two-step water vapor adsorption (182,000 μL g(-1) for 1, 184,000 μL g(-1) for 2, and 1,874,000 μL g(-1) for 3) in the experimental pressure range. Simulation of water-vapor adsorption by the Monte Carlo method (for 1) confirmed the high density of adsorbed water molecules, preferentially in the interlayer space between the 2D layers.

A triangular [Mn3] cluster-based ferrimagnet with significant magnetic entropy change

A triangular [Mn3] cluster-based ferrimagnet [Na2Mn3(SO4)3(μ3-OH)2(μ2-OH2)2]n exhibits a significant magnetocaloric effect (−ΔSm = 14.4 J kg−1 K−1) at 13.5 K.

A family of Fe(3+) based double-stranded helicates showing a magnetocaloric effect, and Rhodamine B dye and DNA binding activities.

Herein, the synthesis, structural characterization, magnetic properties and guest binding activities of four Fe(3+) based double-stranded helicates namely; [Fe2(L)2](ClO4)(Cl)·4(CH3OH)·2(H2O) (), [Fe2(L)2](BF4)2·2(H2O) (), [Fe2(L)2](NO3)2·3(CH3OH)·2(H2O) (), and [Fe2(L)2](Cl)2·2(CH3OH)·4(H2O) () are reported. Complexes have been synthesized using the hydrazide-based ligand H2L (H2L = N'1,N'4-bis(2-hydroxybenzylidene)succinohydrazide) and the corresponding Fe(2+) salts. Each of the independent cationic complexes [Fe2(L)2](2+) shows double-stranded helicates from the self-assembly of the ligand and metal ions in a 2 : 2 ratio, where the individual Fe(3+) centre is lying on a C2-axis and the ligand strands wrap around it. In , ligand L adopts "pseudo-C" conformations and forms a double-stranded dinuclear helicate with a small cage in between them. Moreover, in , each of the independent cationic complexes [Fe2L2](2+) is inherently chiral and possesses P for right-hand and M for left-hand helicity and as a consequence is a racemic solid. Detailed magnetic studies of all the complexes reveal that the Fe(3+) centres are magnetically isolated and isotropic in nature. Estimation of the Magnetocaloric Effect (MCE) from magnetization data unveils a moderate MCE at a temperature of 3 K with magnetic entropy changes (-ΔSm) of 22.9, 27.7, 24.1, 26.5 J kg(-1) K(-1) at a magnetic field of 7 T for complexes , respectively. Also, the variation of the -ΔSm values was justified by considering the parameter of magnetization per unit mass. Stability of all the complexes in solution phase was confirmed by ESI-mass spectrometric analysis and liquid phase FT-IR spectroscopy. Further, the interaction of the complexes with Rhodamine B dye was examined by UV-vis and fluorescence spectroscopic study. The observed blue-shift in the fluorescence study and hyperchromicity and hypochromicity with the appearance of two isosbestic points in the UV-vis study ascertain the interactions of the dye with the complexes. A DNA binding study by absorption spectral titration suggests the weak external intercalation of complex within the nucleotide of calf thymus DNA. Computational study supports the isotropic nature of the metal centres and the consequent high spin multiplicity, which assists the complexes to show significant magnetic entropy changes.