Magnetic Refrigeration Property Research Articles

Two dinuclear lanthanide(III) compounds based on a multidentate ligand: Structures, magnetic refrigeration and slow magnetic relaxation

Two new dinuclear lanthanide(III) compounds based a multidentate Schiff base ligand with the general formula [Ln2(dbm)2L2(CH3OH)2](Ln = Gd (1) and Dy (2), dbm = H2L = N′-(4-(diethylamino)salicylaldehyde)pyridyl-2-carbohydrazide), have been synthesized, structurelly and magnetically characterized. Compounds 1 and 2 are μ2-O bridged dinuclear complexes and each center Ln(III) ion is eight-coordinated with one bidentate dbm−, one CH3OH and two μ2-O bridging Schiff base ligands. Magnetic studies reveal that 1 displays cryogenic magnetic refrigeration property (−ΔSm = 21.1 J kg−1 K−1 for ΔH = 7 T at 2.0 K); while 2 exhibits slow magnetic relaxation behavior under zero dc filed.

Two new coplanar tetranuclear lanthanide complexes (Ln = Gd(III) and Dy(III)) with magnetic refrigeration and slow magnetic relaxation behaviors

Two novel tetranuclear Ln (III) complexes, namely [Ln4(µ3-OH)2(tmhd)4L6] (Ln(III) = Gd (1), Dy (2); HL = 5-(2-thenylidene)-8-hydroxylquinoline; tmhd = 5-(4-methylbenzylidene)-8-hydroxylquinoline), were synthesized and their structures and magnetic properties were characterized. The two complexes are both composed of one planar [Ln4(µ3-OH)2] center, in which adjacent eight-coordinated Ln(III) ions are bridged by phenoxy oxygen atoms and µ3-OH molecules. A magnetic investigation revealed that complex 1 displays cryogenic magnetic refrigeration properties with −ΔSm = 21.13 J kg−1 K−1 at T = 2.5 K and ΔH = 7.0 T. For complex 2, a slow magnetic relaxation behavior with an energy barrier of 67.8 K was observed.

Four tetra-nuclear lanthanide complexes based on 8-hydroxyquinolin derivatives: magnetic refrigeration and single-molecule magnet behaviour

Four lanthanide complexes were fabricated and characterized. 1 exhibits cryogenic magnetic refrigeration property and 3 displays slow relaxation of the magnetization.

Structures and magnetic properties of two series of phenoxo-O bridged Ln2 compounds: Two Gd2 compounds displaying magnetic refrigeration properties

Two series of lanthanide dinuclear compounds, namely[Ln(hfac)2L]2 (LnIII=Gd (1), Ho (2) and Er (3), hfac=hexafluoroacetylacetonate, HL=2-[[(4-iodophenyl)imino]methyl]-8-hydroxyquinoline) and [Ln(tfac)2L]2 (LnIII=Gd (4) and Tm (5), tfac=trifluoroacetylacetonate), have been synthesized and characterized by elemental analysis, IR, PXRD, UV–Vis and single crystal X-ray diffraction. Single-crystal X-ray diffraction analysis shows that the two series of Ln2 compounds have very similar structures and each eight-coordinated center Ln(III) ion is in a slightly distorted dodecahedral geometry with two bidentate β-diketonate coligands and two μ2-O bridging 8-hydroxyquinoline Schiff base ligands. The magnetic study reveals that 1 and 4 display cryogenic magnetic refrigeration properties with maximum −ΔSm values of 16.41 and 18.32JK−1kg−1 at 2.0K and 7.0T, respectively.

Magnetic refrigeration and single-molecule magnet behaviour of two lanthanide dinuclear complexes (Ln = GdIII, TbIII) based on 8-hydroxyquinolin derivatives

Two dinuclear lanthanide(III) complexes, namely, [Ln2(bfa)4L2]·CH2Cl2 (Ln(III)=Gd (1) and Tb (2), bfa=benzoyltrifluoroacetone and HL=2-[[(4-methylphenyl)imino]methyl]-8-hydroxyquinoline), have been synthesized, structurally and magnetically characterized. 1 and 2 are phenoxo-O bridged dinuclear complexes and each center Ln(III) ion is eight-coordinated with two bidentate bfa and two μ2-O bridging 8-hydroxyquinoline Schiff base ligands. Magnetic studies reveal that 1 displays cryogenic magnetic refrigeration property (−ΔSm=18.5Jkg−1K−1 for ΔH=7T at 2K); while 2 exhibits single-molecule magnet behavior with the anisotropic barriers (ΔE/kB) of 9.93K.

Structures, luminescence properties, magnetocaloric effect and slow magnetic relaxation of three Ln (III) complexes based on 8‑hydroxyquinoline Schiff-base ligand

Three new dinuclear lanthanide compounds, [Ln(hfac)2L]2 (Ln(III)=Gd (1), Tb (2) and Er (3), hfac=hexafluoroacetylacetonate and HL=2-[(4-ethylphenyl)imino]methyl-8-hydroxyquinoline), have been synthesized and characterized by elemental analysis, IR, PXRD and single crystal X-ray diffraction. The X-ray structural analysis exhibit that 1–3 are phenoxo-O-bridged dinuclear complexes and central Ln(III) ions are eight-coordinated with two bidentate hfac− and two μ2-O bridging 8-hydroxyquinoline Schiff base ligands. Magnetic measurements indicate that 1 displays cryogenic magnetic refrigeration properties with maximum −ΔSm value of 19.94JK−1kg−1 at 2K and 7T; whereas 2 shows slow magnetic relaxation with energy barriers of 15.3K and τ0=3.34×10−6s. Additionally, solid-state photoluminescence property reveals that 2 displays the characteristic TbIII luminescence at room temperature.

Two Gd2 compounds constructed by 8-hydroxyquinoline Schiff base ligands: Synthesis, structure, and magnetic refrigeration

Two new Gd2 compounds having formulae, [Gd2(hfac)4(L1)2] (1) and [Gd2(hfac)4(L2)2] (2) (hfac=hexafluoroacetylacetonate, HL1=2-[4-methylaniline-imino]methyl]-8-hydroxyquinoline and HL2=2-[(3,4-dimethylaniline)-imino]methyl]-8-hydroxyquinoline), have been successfully synthesized via applying two different 8-hydroxyquinoline Schiff base ligands, and further characterized by crystallography. Structural analysis shows that both of 1 and 2 are phenoxo-O bridged dinuclear complexes. The magnetic study reveal that 1 and 2 display cryogenic magnetic refrigeration properties with maximum −ΔSm=17.66Jkg−1K−1 at 2K and 7T for 1 and −ΔSm=14.81Jkg−1K−1 at 3K and 7T for 2.

Fine-tuning the magnetocaloric effect and SMMs behaviors of coplanar RE4 complexes by β-diketonate coligands

By introducing different β-diketonate coligands, Gd4 complexes show cryogenic magnetic refrigeration properties, whereas Dy4 clusters exhibit different SMMs behaviors.

Seven phenoxido-bridged complexes encapsulated by 8-hydroxyquinoline Schiff base derivatives and β-diketone ligands: single-molecule magnet, magnetic refrigeration and luminescence properties

Seven dinuclear complexes based on 8-hydroxyquinoline Schiff base derivatives and β-diketone ligands, [RE2(hfac)4L2] (RE = Y (1), Gd (2), Tb (3), Dy (4), Ho (5), Er (6) and Lu (7); hfac(-) = hexafluoroacetylacetonate; HL = 2-[(4-chloro-phenylimino)-methyl]-8-hydroxyquinoline), have been synthesized, and structurally and magnetically characterized. Complexes 1-7 have similar dinuclear structures, in which each RE(III) ion is eight coordinated by two L(-) and two hfac(-) ligands in a distorted dodecahedron geometry. The luminescence spectra indicate that complex 3 exhibits characteristic Tb(III) ion luminescence, while 1 and 7 show HL ligand luminescence. The magnetic studies reveal that 2 features a magnetocaloric effect with the magnetic entropy change of -ΔSm = 16.83 J kg(-1) K(-1) at 2 K for ΔH = 8 T, and 4 displays slow magnetic relaxation behavior with the anisotropic barrier of 6.7 K and pre-exponential factor τ0 = 5.3 × 10(-6) s.

Ligand Field Affected Single-Molecule Magnet Behavior of Lanthanide(III) Dinuclear Complexes with an 8-Hydroxyquinoline Schiff Base Derivative as Bridging Ligand.

New dinuclear lanthanide(III) complexes based on an 8-hydroxyquinoline Schiff base derivative and β-diketonate ligands, [Ln2(hfac)4(L)2] (Ln(III) = Gd (1), Tb (2), Dy (3), Ho (4), Er (5)), [Ln2(tfac)4(L)2] (Ln(III) = Gd (6), Tb (7), Dy (8), Ho (9)), and [Dy(bfac)4(L)2·C7H16] (10) (L = 2-[[(4-fluorophenyl)imino] methyl]-8-hydroxyquinoline, hfac = hexafluoroacetylacetonate, tfac = trifluoroacetylacetonate, and bfac = benzoyltrifluoroacetone), have been synthesized. The single-crystal X-ray diffraction data show that complexes 1-10 are phenoxo-O-bridged dinuclear complexes; each eight-coordinated center Ln(III) ion is in a slightly distorted dodecahedral geometry with two bidentate β-diketonate coligands and two μ2-O bridging 8-hydroxyquinoline Schiff base derivative ligands. The magnetic study reveals that 1 and 6 display cryogenic magnetic refrigeration properties, whereas complexes 3, 8, and 10 show different SMM behaviors with energy barriers of 6.77 K for 3, 19.83 K for 8, and 25.65 K for 10. Meanwhile, slow magnetic relaxation was observed in 7, while no out-of-phase alternating-current signals were found for 2. The different dynamic magnetic behaviors of two Tb2 complexes and the three Dy2 complexes mainly derive from the tiny crystal structure changes around the Ln(III) ions. It is also proved that the β-diketonate coligands can play an important role in modulating magnetic dynamics of the lanthanide 8-hydroxyquinoline Schiff base derivative system.

Enhanced magnetic refrigeration properties in Mn-rich Ni-Mn-Sn ribbons by optimal annealing.

The influence of annealing time on temperature range of martensitic phase transition (ΔTA-M), thermal hysteresis (ΔThys), magnetic hysteresis loss (ΔMhys), magnetic entropy change (ΔSM) and relative refrigeration capacity (RC) of the Mn-rich Ni43Mn46Sn11 melt spun ribbons have been systematically studied. By optimal annealing, an extremely large ΔSM of 43.2 J.kg−1K−1 and a maximum RC of 221.0 J.kg−1 could be obtained respectively in a field change of 5 T. Both ΔTA-M and ΔThys decreases after annealing, while ΔMhys and ΔSM first dramatically increase to a maximum then degenerates as increase of annealing time. A large effective cooling capacity (RCeff) of 115.4 J.kg−1 was achieved in 60 min annealed ribbons, which increased 75% compared with that unannealed ribbons. The evolution of magnetic properties and magnetocaloric effect has been discussed and proved by atomic ordering degree, microstructure and composition analysis.

Lanthanide coordination polymers with "fsy-type" topology based on 4,4'-azobenzoic acid: syntheses, crystal structures, and magnetic properties.

Seven lanthanide coordination polymers (CPs), [Ln2(azdc)3(DMA)2]n·2n(DMA) (Ln = Sm(III) for 1, Eu(III) for 2, Gd(III) for 3, Tb(III) for 4, Dy(III) for 5, Ho(III) for 6, Er(III) for 7; H2azdc = 4,4'-azobenzoic acid, DMA = N,N-dimethylacetamide), have been successfully prepared with high yields via solvothermal methods and further studied by elemental analyses (EA), powder X-ray diffraction (PXRD), UV-vis spectra, photoluminescent spectra, thermogravimetric analyses (TGA), variable-temperature in situ PXRD analyses, and single-crystal X-ray diffraction. CPs 1-7 all consist of unique 1D lanthanide-carboxylate building units [Ln2(CO2)6]n constructed from the adjacent Ln(III) cations and carboxyl groups of the H2azdc ligands, which can further generate 3D frameworks with "fsy"-type topological structures via the link of azdc(2-). Furthermore, variable-temperature magnetic susceptibility measurements of 1-7 have been investigated. The results indicate that unusual ferromagnetic coupling between adjacent Gd(III) cations exists in 3, which is rarely reported in the Gd(III) complexes only bridged by μ1,3-COO groups. Meanwhile, the magnetic study reveals that 3 displays cryogenic magnetic refrigeration property, whereas 5 shows magnetic dynamics at low temperature.

A novel preparation method and magnetic properties of NaZn13-type La(Fe, Si)13 compounds

The single-phase NaZn13-type La(Fe,Si)13 compounds have been successfully synthesized by using a novel stoichiometry chemical ratio 1:11 of La and (Fe, Si). By this method, the as-cast compounds directly formed into NaZn13-type single phase from arc-melting when the Si content in the range of 2.2 to 2.4, which is the first time to obtain NaZn13-type single phase without any heat treatments. Meanwhile, when the Si content x⩽1.4, all the compounds crystallize in the NaZn13-type cubic structure with small amounts of α-Fe impurity phase after annealed at 1373K for 100h. Among them, the LaFe9.8Si1.2 compound shows a thermal and field-induced first-order phase transition around its transition temperature. Its maximal magnetic entropy-change reaches to 14.8J/kgK under a field change of 1.5 T, showing an excellent magnetic refrigeration property. Thus, the chemical ratio of 1:11 as a new stoichiometry provides a novel and rapid preparation method for single-phase NaZn13-type La(Fe,Si)13 compounds with excellent properties.