The Experts below are selected from a list of 19482 Experts worldwide ranked by ideXlab platform
David N. Hendrickson - One of the best experts on this subject based on the ideXlab platform.
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Nonexponential Magnetization Relaxation in a manganese single-molecule magnet
Physica B-condensed Matter, 2003Co-Authors: Akira Yamaguchi, Hiroyuki Mitamura, Nobuo Mori, Tsuneaki Goto, Hidehiko Ishimoto, Motohiro Nakano, Jae Yoo, David N. Hendrickson, Euan K. Brechin, George ChristouAbstract:Abstract The Magnetization Relaxation in a tetranuclear manganese cluster Mn4(pdmH) has been investigated with an extraction and a Faraday magnetometer at 0.14– 0.75 K . The Relaxation curves in the tunneling regime show the “square-root time” dependence for a short time after reversing the Magnetization. This fact suggests the hyperfine and inter-cluster dipolar interactions play important roles for the Relaxation.
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Single-Molecule Magnets: Jahn-Teller Isomerism and the Origin of Two Magnetization Relaxation Processes in Mn12 Complexes
arXiv: Condensed Matter, 2001Co-Authors: Sheila M. J. Aubin, George Christou, Ziming Sun, Hilary J. Eppley, E. M. Rumberger, Ilia A. Guzei, Kirsten Folting, Peter Gantzel, Arnold L. Rheingold, David N. HendricksonAbstract:New Mn12 single-molecule magnets (SMM's) with the composition [Mn12O12(O2CR)16(H2O)4] were prepared and structurally characterized. Complexes of this type can exhibit two out-of-phase ac magnetic susceptibility signals, one in the 4-7 K region and the other in the 2-3 K region. The origin of the two Magnetization Relaxation processes was systematically examined. The X-ray structures of two isomeric forms of a Mn12 SMM are given. One complex has an abnormal Jahn-Teller distortion axis. The Magnetization hysteresis loops for the two isomers are quite different.
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Single-Molecule Magnets: Jahn−Teller Isomerism and the Origin of Two Magnetization Relaxation Processes in Mn12 Complexes
Polyhedron, 2001Co-Authors: Sheila M. J. Aubin, George Christou, Ziming Sun, Hilary J. Eppley, E. M. Rumberger, Ilia A. Guzei, Kirsten Folting, Peter Gantzel, Arnold L. Rheingold, David N. HendricksonAbstract:Several single-molecule magnets with the composition [Mn12O12(O2CR)16(H2O)x] (x = 3 or 4) exhibit two out-of-phase ac magnetic susceptibility signals, one in the 4−7 K region and the other in the 2−3 K region. New Mn12 complexes were prepared and structurally characterized, and the origin of the two Magnetization Relaxation processes was systematically examined. Different crystallographic forms of a Mn12 complex with a given R substituent exist where the two forms have different compositions of solvent molecules of crystallization and this results in two different arrangements of bound H2O and carboxylate ligands for the two crystallographically different forms with the same R substituent. The X-ray structure of cubic crystals of [Mn12O12(O2CEt)16(H2O)3]· 4H2O (space group P1) (complex 2a) has been reported previously. The more prevalent needle-form of [Mn12O12(O2CEt)16(H2O)3] (complex 2b) crystallizes in the monoclinic space group P21/c, which at −170 °C has a = 16.462(7) A, b = 22.401(9) A, c = 20.766(...
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single molecule magnets jahn teller isomerism and the origin of two Magnetization Relaxation processes in mn12 complexes
Inorganic Chemistry, 2001Co-Authors: Sheila M. J. Aubin, George Christou, Ziming Sun, Hilary J. Eppley, E. M. Rumberger, Ilia A. Guzei, Kirsten Folting, Peter Gantzel, Arnold L. Rheingold, David N. HendricksonAbstract:Several single-molecule magnets with the composition [Mn12O12(O2CR)16(H2O)x] (x = 3 or 4) exhibit two out-of-phase ac magnetic susceptibility signals, one in the 4−7 K region and the other in the 2−3 K region. New Mn12 complexes were prepared and structurally characterized, and the origin of the two Magnetization Relaxation processes was systematically examined. Different crystallographic forms of a Mn12 complex with a given R substituent exist where the two forms have different compositions of solvent molecules of crystallization and this results in two different arrangements of bound H2O and carboxylate ligands for the two crystallographically different forms with the same R substituent. The X-ray structure of cubic crystals of [Mn12O12(O2CEt)16(H2O)3]· 4H2O (space group P1) (complex 2a) has been reported previously. The more prevalent needle-form of [Mn12O12(O2CEt)16(H2O)3] (complex 2b) crystallizes in the monoclinic space group P21/c, which at −170 °C has a = 16.462(7) A, b = 22.401(9) A, c = 20.766(...
George Christou - One of the best experts on this subject based on the ideXlab platform.
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Slow Magnetization Relaxation in unprecedented Mn(III)4Dy(III)3 and Mn(III)4Dy(III)5 clusters from the use of N-salicylidene-o-aminophenol.
Inorganic chemistry, 2013Co-Authors: Dimitris I. Alexandropoulos, George Christou, Luís Cunha-silva, Albert Escuer, Tu N. Nguyen, Theodoros F. Zafiropoulos, Theocharis C. StamatatosAbstract:The first use of N-salicylidene-o-aminophenol in 3d/4f chemistry has led to Mn(III)(4)Dy(III)(5) and Mn(III)(4)Dy(III)(3) clusters with unprecedented metal topologies and stoichiometries; both compounds exhibit out-of-phase signals indicative of the slow Magnetization Relaxation of a single-molecule magnet.
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a caveat for single molecule magnetism non linear arrhenius plots
arXiv: Mesoscale and Nanoscale Physics, 2009Co-Authors: Christos Lampropoulos, Stephen Hill, George ChristouAbstract:The Magnetization Relaxation of Mn12 single-molecule magnets (SMMs) does not follow a simple Arrhenius law, even for data collected at low frequencies (5-1500 Hz) due to contributions from Relaxation pathways via excited states with larger thermal barriers, but much faster attempt rates. A modified Arrhenius equation is presented as a means to overcome this problem and obtain a more reliable limiting value for the barrier to Magnetization Relaxation associated with the ground S=10 state.
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Nonexponential Magnetization Relaxation in a manganese single-molecule magnet
Physica B-condensed Matter, 2003Co-Authors: Akira Yamaguchi, Hiroyuki Mitamura, Nobuo Mori, Tsuneaki Goto, Hidehiko Ishimoto, Motohiro Nakano, Jae Yoo, David N. Hendrickson, Euan K. Brechin, George ChristouAbstract:Abstract The Magnetization Relaxation in a tetranuclear manganese cluster Mn4(pdmH) has been investigated with an extraction and a Faraday magnetometer at 0.14– 0.75 K . The Relaxation curves in the tunneling regime show the “square-root time” dependence for a short time after reversing the Magnetization. This fact suggests the hyperfine and inter-cluster dipolar interactions play important roles for the Relaxation.
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Single-Molecule Magnets: Jahn-Teller Isomerism and the Origin of Two Magnetization Relaxation Processes in Mn12 Complexes
arXiv: Condensed Matter, 2001Co-Authors: Sheila M. J. Aubin, George Christou, Ziming Sun, Hilary J. Eppley, E. M. Rumberger, Ilia A. Guzei, Kirsten Folting, Peter Gantzel, Arnold L. Rheingold, David N. HendricksonAbstract:New Mn12 single-molecule magnets (SMM's) with the composition [Mn12O12(O2CR)16(H2O)4] were prepared and structurally characterized. Complexes of this type can exhibit two out-of-phase ac magnetic susceptibility signals, one in the 4-7 K region and the other in the 2-3 K region. The origin of the two Magnetization Relaxation processes was systematically examined. The X-ray structures of two isomeric forms of a Mn12 SMM are given. One complex has an abnormal Jahn-Teller distortion axis. The Magnetization hysteresis loops for the two isomers are quite different.
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Single-Molecule Magnets: Jahn−Teller Isomerism and the Origin of Two Magnetization Relaxation Processes in Mn12 Complexes
Polyhedron, 2001Co-Authors: Sheila M. J. Aubin, George Christou, Ziming Sun, Hilary J. Eppley, E. M. Rumberger, Ilia A. Guzei, Kirsten Folting, Peter Gantzel, Arnold L. Rheingold, David N. HendricksonAbstract:Several single-molecule magnets with the composition [Mn12O12(O2CR)16(H2O)x] (x = 3 or 4) exhibit two out-of-phase ac magnetic susceptibility signals, one in the 4−7 K region and the other in the 2−3 K region. New Mn12 complexes were prepared and structurally characterized, and the origin of the two Magnetization Relaxation processes was systematically examined. Different crystallographic forms of a Mn12 complex with a given R substituent exist where the two forms have different compositions of solvent molecules of crystallization and this results in two different arrangements of bound H2O and carboxylate ligands for the two crystallographically different forms with the same R substituent. The X-ray structure of cubic crystals of [Mn12O12(O2CEt)16(H2O)3]· 4H2O (space group P1) (complex 2a) has been reported previously. The more prevalent needle-form of [Mn12O12(O2CEt)16(H2O)3] (complex 2b) crystallizes in the monoclinic space group P21/c, which at −170 °C has a = 16.462(7) A, b = 22.401(9) A, c = 20.766(...
Sheila M. J. Aubin - One of the best experts on this subject based on the ideXlab platform.
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Single-Molecule Magnets: Jahn-Teller Isomerism and the Origin of Two Magnetization Relaxation Processes in Mn12 Complexes
arXiv: Condensed Matter, 2001Co-Authors: Sheila M. J. Aubin, George Christou, Ziming Sun, Hilary J. Eppley, E. M. Rumberger, Ilia A. Guzei, Kirsten Folting, Peter Gantzel, Arnold L. Rheingold, David N. HendricksonAbstract:New Mn12 single-molecule magnets (SMM's) with the composition [Mn12O12(O2CR)16(H2O)4] were prepared and structurally characterized. Complexes of this type can exhibit two out-of-phase ac magnetic susceptibility signals, one in the 4-7 K region and the other in the 2-3 K region. The origin of the two Magnetization Relaxation processes was systematically examined. The X-ray structures of two isomeric forms of a Mn12 SMM are given. One complex has an abnormal Jahn-Teller distortion axis. The Magnetization hysteresis loops for the two isomers are quite different.
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Single-molecule magnets: Jahn-Teller isomerism and the origin of two Magnetization Relaxation processes in Mn12 complexes.
Inorganic chemistry, 2001Co-Authors: Sheila M. J. Aubin, Ziming Sun, Hilary J. Eppley, E. M. Rumberger, Ilia A. Guzei, Kirsten Folting, Peter Gantzel, Arnold L. Rheingold, G Christou, D N HendricksonAbstract:Several single-molecule magnets with the composition [Mn12O12(O2CR)16(H2O)x] (x = 3 or 4) exhibit two out-of-phase ac magnetic susceptibility signals, one in the 4-7 K region and the other in the 2-3 K region. New Mn12 complexes were prepared and structurally characterized, and the origin of the two Magnetization Relaxation processes was systematically examined. Different crystallographic forms of a Mn12 complex with a given R substituent exist where the two forms have different compositions of solvent molecules of crystallization and this results in two different arrangements of bound H2O and carboxylate ligands for the two crystallographically different forms with the same R substituent. The X-ray structure of cubic crystals of [Mn12O12(O2CEt)16(H2O)3]. 4H2O (space group P1) (complex 2a) has been reported previously. The more prevalent needle-form of [Mn12O12(O2CEt)16(H2O)3] (complex 2b) crystallizes in the monoclinic space group P2(1)/c, which at -170 degrees C has a = 16.462(7) A, b = 22.401(9) A, c = 20.766(9) A, beta = 103.85(2) degrees, and Z = 4. The arrangements of H2O and carboxylate ligands on the Mn12 molecule are different in the two crystal forms. The complex [Mn12O12-(O2)CC6H4-p-Cl)16(H2O)4].8CH2Cl2 (5) crystallizes in the monoclinic space group C2/c, which at -172 degrees C has a = 29.697(9) A, b = 17.708(4) A, c = 30.204(8) A, beta = 102.12(2) degrees, and Z = 4. The ac susceptibility data for complex 5 show that it has out-of-phase signals in both the 2-3 K and the 4-7 K ranges. X-ray structures are also reported for two isomeric forms of the p-methylbenzoate complex. [Mn12O12(O2CC6H4-p-Me)16(H2O)4]. (HO2CC6H4-p-Me) (6) crystallizes in the monoclinic space group C2/c, which at 193 K has a = 40.4589(5) A, b = 18.2288(2) A, c = 26.5882(4) A, beta = 125.8359(2) degrees, and Z = 4. [Mn12O12(O2CC6H4-p-Me)16(H2O)4].3(H2O) (7) crystallizes in the monoclinic space group I2/a, which at 223 K has a = 29.2794(4) A, b = 32.2371(4) A, c = 29.8738(6) A, beta = 99.2650(10) degrees, and Z = 8. The Mn12 molecules in complexes 6 and 7 differ in their arrangements of the four bound H2O ligands. Complex 6 exhibits an out-of-phase ac peak (chi(M)' ') in the 2-3 K region, whereas the hydrate complex 7 has a chi(M)' ' signal in the 4-7 K region. In addition, however, in complex 6, one Mn(III) ion has an abnormal Jahn-Teller distortion axis oriented at an oxide ion, and thus 6 and 7 are Jahn-Teller isomers. This reduces the symmetry of the core of complex 6 compared with complex 7. Thus, complex 6 likely has a larger tunneling matrix element and this explains why this complex shows a chi(M)' ' signal in the 2-3 K region, whereas complex 7 has its chi(M)' ' peak in the 4-7 K region, i.e., the rate of tunneling of Magnetization is greater in complex 6 than complex 7. Detailed 1H NMR experiments (2-D COSY and TOCSY) lead to the assignment of all proton resonances for the benzoate and p-methyl-benzoate Mn12 complexes and confirm the structural integrity of the (Mn12O12) complexes upon dissolution. In solution there is rapid ligand exchange and no evidence for the different isomeric forms of Mn12 complexes seen in the solid state.
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Single-Molecule Magnets: Jahn−Teller Isomerism and the Origin of Two Magnetization Relaxation Processes in Mn12 Complexes
Polyhedron, 2001Co-Authors: Sheila M. J. Aubin, George Christou, Ziming Sun, Hilary J. Eppley, E. M. Rumberger, Ilia A. Guzei, Kirsten Folting, Peter Gantzel, Arnold L. Rheingold, David N. HendricksonAbstract:Several single-molecule magnets with the composition [Mn12O12(O2CR)16(H2O)x] (x = 3 or 4) exhibit two out-of-phase ac magnetic susceptibility signals, one in the 4−7 K region and the other in the 2−3 K region. New Mn12 complexes were prepared and structurally characterized, and the origin of the two Magnetization Relaxation processes was systematically examined. Different crystallographic forms of a Mn12 complex with a given R substituent exist where the two forms have different compositions of solvent molecules of crystallization and this results in two different arrangements of bound H2O and carboxylate ligands for the two crystallographically different forms with the same R substituent. The X-ray structure of cubic crystals of [Mn12O12(O2CEt)16(H2O)3]· 4H2O (space group P1) (complex 2a) has been reported previously. The more prevalent needle-form of [Mn12O12(O2CEt)16(H2O)3] (complex 2b) crystallizes in the monoclinic space group P21/c, which at −170 °C has a = 16.462(7) A, b = 22.401(9) A, c = 20.766(...
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single molecule magnets jahn teller isomerism and the origin of two Magnetization Relaxation processes in mn12 complexes
Inorganic Chemistry, 2001Co-Authors: Sheila M. J. Aubin, George Christou, Ziming Sun, Hilary J. Eppley, E. M. Rumberger, Ilia A. Guzei, Kirsten Folting, Peter Gantzel, Arnold L. Rheingold, David N. HendricksonAbstract:Several single-molecule magnets with the composition [Mn12O12(O2CR)16(H2O)x] (x = 3 or 4) exhibit two out-of-phase ac magnetic susceptibility signals, one in the 4−7 K region and the other in the 2−3 K region. New Mn12 complexes were prepared and structurally characterized, and the origin of the two Magnetization Relaxation processes was systematically examined. Different crystallographic forms of a Mn12 complex with a given R substituent exist where the two forms have different compositions of solvent molecules of crystallization and this results in two different arrangements of bound H2O and carboxylate ligands for the two crystallographically different forms with the same R substituent. The X-ray structure of cubic crystals of [Mn12O12(O2CEt)16(H2O)3]· 4H2O (space group P1) (complex 2a) has been reported previously. The more prevalent needle-form of [Mn12O12(O2CEt)16(H2O)3] (complex 2b) crystallizes in the monoclinic space group P21/c, which at −170 °C has a = 16.462(7) A, b = 22.401(9) A, c = 20.766(...
Lucica Miu - One of the best experts on this subject based on the ideXlab platform.
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DC Magnetization Relaxation and the AC Susceptibility of YBCO Films with Strong Pinning
Journal of Superconductivity and Novel Magnetism, 2014Co-Authors: Lucica Miu, I Ivan, Paolo Mele, A. M. Ionescu, Dana MiuAbstract:AC susceptibility and DC Magnetization Relaxation measurements have been performed for YBa2Cu3O7 films containing BaZrO3 nanorods preferentially oriented along the c axis, with the external magnetic field perpendicular to the film surface. It was found that the effective vortex activation energy U e supplied by the standard analysis of the frequency dependent AC magnetic response remains very high even in the vicinity of the irreversibility line indicated by the DC Relaxation. We show that the large U e values appearing in the AC signal are related to the pinning enhanced viscous drag and significant vortex velocities.
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Vortex creep crossover in YBCO/PrBCO superlattices during standard Magnetization Relaxation measurements
Superconductor Science and Technology, 2011Co-Authors: A. El Tahan, I Ivan, Petre Badica, Gerhard Jakob, Dana Miu, Lucica MiuAbstract:We investigated the Relaxation of the irreversible Magnetization in a series of 200?nm thick YBa2Cu3O7/PrBa2Cu3O7 [(YBCO)n/(PrBCO)m] superlattices, where the thickness m of the nonsuperconducting PrBCO layer (measured in unit cells) was kept to m = 4 (sufficient to decouple the superconducting YBCO layers), whereas the thickness n of the YBCO layer was varied between 2 and 20 unit cells. The analysis of standard zero-field-cooling dc Magnetization Relaxation data obtained in the low temperature T region with the applied magnetic field H oriented along the c axis reveals the occurrence of a crossover elastic (collective) vortex creep at low T?plastic vortex creep at high T, generated by the T dependent macroscopic currents induced in the sample during measurements. For thin superlattices (n < 20) the creep crossover temperature , and Tcr decreases linearly with increasing ln(H) for a fixed n. This crossover represents an alternative to the elastic vortex glass behavior reported for superlattices, as well as to 'quantum vortex creep' at unexpectedly high T inferred for thin films. We also discuss the absence of an increase of the magnetically determined critical current density with decreasing YBCO thickness in our superlattices, which apparently contradicts the collective pinning theories.
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Origin of the fast Magnetization Relaxation at low temperatures in HTS with strong pinning
Physica C: Superconductivity and its Applications, 2010Co-Authors: Lucica Miu, I Ivan, Petre Badica, Gerhard Jakob, Dana Miu, Paolo Mele, Kaname Matsumoto, Masashi Mukaida, Yutaka Yoshida, T. HorideAbstract:The temperature T variation of the normalized Magnetization Relaxation rate S in high-temperature superconductors (HTS) with strong vortex pinning exhibits a maximum in the low-T range. This was reported for various HTS, and the origin of the faster Relaxation at low T appearing in standard Magnetization Relaxation measurements was usually related to specific pinning properties of the investigated specimens. Since the observed behaviour seems to be characteristic to all HTS with enhanced pinning (generated by random and/or correlated disorder), we show that the S(T) maximum can be explained in terms of classic collective vortex creep. The influence of thermo-magnetic instabilities in the low-T range is also evidenced. The collective (elastic) creep regime is generated by the T dependent macroscopic currents induced in the sample during standard Magnetization measurements.
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Origin of the plateau in the temperature dependence of the normalized Magnetization Relaxation rate in disordered high-temperature superconductors
Physical Review B, 2008Co-Authors: Lucica Miu, Gerhard Jakob, Dana Miu, A. El Tahan, Traian Petrisor, H. AdrianAbstract:The temperature $T$ dependence of the normalized Magnetization Relaxation rate $S$ in optimally doped ${\text{YBa}}_{2}{\text{Cu}}_{3}{\text{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ films with the external dc magnetic field $H$ oriented along the $c$ axis exhibits the well-known plateau in the intermediate $T$ range, associated with the presence of elastic (collective) vortex creep. The disappearance of the $S(T)$ plateau in the high-$H$ domain $(H\ensuremath{\ge}20\text{ }\text{kOe})$ is not completely understood. We show that in the case of high-temperature superconductors with significant quenched disorder the $S(T)$ plateau is directly related to a crossover in the vortex-creep process generated by the macroscopic currents induced in the sample. In dc Magnetization measurements the creep-crossover temperature decreases rapidly with increasing $H$, reaching the low-$T$ region where the Magnetization decay is dominated by micro flux jumps. Consequently, at high $H$ no well-defined elastic-creep domain is present and the $S(T)$ plateau disappears.
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Analysis of Magnetization Relaxation in MgB2 bulk samples obtained by electric-field assisted sintering
Physica C: Superconductivity, 2008Co-Authors: Lucica Miu, I Ivan, Petre Badica, Gerhard Jakob, Dana Miu, Gheorghe Aldica, J. R. Groza, H. AdrianAbstract:Abstract The Relaxation of the irreversible Magnetization of MgB2 bulk samples obtained by electric-field assisted sintering was investigated using the SQUID magnetometry for a magnetic field H up to 50 kOe applied in zero-field-cooling conditions. We observed a crossover plastic creep at high temperatures T-elastic creep at low T, described by H ∝ T−2 in the low T range, which appears to be caused by the macroscopic currents induced in the sample during Magnetization measurements. By decreasing T below this line the determined creep exponent rapidly overcomes the widely accepted theoretical values for elastic (collective) pinning. This behaviour can easily be explained through the occurrence of micro flux jumps, leading to a finite Magnetization Relaxation rate in the low-T limit.
Gopalan Rajaraman - One of the best experts on this subject based on the ideXlab platform.
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The effect of the electronic structure and flexibility of the counteranions on Magnetization Relaxation in [Dy(L)2(H2O)5]3+ (L = phosphine oxide derivative) pentagonal bipyramidal SIMs
Inorganic Chemistry Frontiers, 2020Co-Authors: Ismael F. Díaz-ortega, Gopalan Rajaraman, Juan Manuel Herrera, Sourav Dey, Hiroyuki Nojiri, Enrique ColacioAbstract:We report here a new DyIII-SIM [Dy(OPCy3)2(H2O)5](CF3SO3)3·2OPCy3 (OPCy3 = tricyclohexylphosphine oxide) with a pentagonal bipyramidal geometry, which exhibits a blocking temperature TB = 8.5 K and an anisotropy barrier Ueff = 562 K. Ab initio calculations show that this complex exhibits the largest Ucalc = 732 K among the DyIII-SIM complexes containing the [Dy(L)2(H2O)5]3+ (L = phosphine oxide derivative) cationic unit, which is essentially due to the electronic effects of the triflate anion that increase the charge difference between the oxygen atoms of the ligands L coordinated in axial positions and those belonging to the equatorial water molecules. This charge difference enhancement, which is also reflected in a larger difference between the corresponding Dy–O distances (Δ), appears to be the driving force to increase the Ucalc value. The comparatively smaller experimental Ueff value observed for this compound has been justified by the flexibility of the structural network due to the size of the triflate counteranions. The absence of a clear correlation between TB and Ueff (or Ucalc) suggests the involvement of Raman and QTM mechanisms in the Magnetization Relaxation process.
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Substituted versus Naked Thiourea Ligand Containing Pseudotetrahedral Cobalt(II) Complexes: A Comparative Study on Its Magnetization Relaxation Dynamics Phenomenon.
Inorganic chemistry, 2018Co-Authors: Shefali Vaidya, Pragya Shukla, Shalini Tripathi, Gopalan Rajaraman, Eric Rivière, Talal Mallah, Maheswaran ShanmugamAbstract:A series of mononuclear tetrahedral cobalt(II) complexes with the general molecular formula [Co(L1)2X2] [where L1 = tetramethylthiourea ([(CH3)2N]2C═S) and X = Cl (1), Br (2), and I (3)] were isolated, and their structures were characterized by single-crystal X-ray diffraction. The experimental direct-current magnetic data are excellently reproduced by fitting both χM T( T) and M( H) simultaneously using the spin Hamiltonian (SH) parameters D1 = -18.1 cm-1 and g1,iso = 2.26, D2 = -16.4 cm-1 and g2,iso = 2.33, and D3 = -22 cm-1 and g3,iso = 2.4 for 1-3, respectively, and the sign of D was unambiguously confirmed from X-band electron paramagnetic resonance measurements. The effective energy barrier extracted for the magnetically diluted complexes 1-3 (10%) is larger than the barrier observed for the pure samples and implies a nonzero contribution of dipolar interaction to the Magnetization Relaxation dynamics. The SH parameters extracted for the three complexes drastically differ from their respective parent complexes that possess the general molecular formula [Co(L)2X2] [where L = thiourea [(NH2)2C═S] and X = Cl (1a), Br (2a), and I (3a)], which is rationalized by detailed ab initio calculations. An exhaustive theoretical study reveals that both the ground and excited states are not pure but rather multideterminental in nature (1-3). Noticeably, the substitution of L by L1 induces structural distortion in 1-3 on the level of the secondary coordination sphere compared to 1a-3a. This distortion leads to an overall reduction in | E/ D| of 1-3 compared to 1a-3a. This may be one of the reasons for the origin of the slower Relaxation times of 1-3 compared to 1a-3a.
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role of magnetic exchange interactions in the Magnetization Relaxation of 3d 4f single molecule magnets a theoretical perspective
Chemistry: A European Journal, 2016Co-Authors: Saurabh Kumar Singh, Mohammad Faizan Beg, Gopalan RajaramanAbstract:Combined density functional and ab initio calculations are performed on two isomorphous tetranuclear {Ni3 (III) Ln(III) } star-type complexes [Ln=Gd (1), Dy (2)] to shed light on the mechanism of magnetic exchange in 1 and the origin of the slow Magnetization Relaxation in complex 2. DFT calculations correctly reproduce the sign and magnitude of the J values compared to the experiments for complex 1. Acute ∢Ni-O-Gd bond angles present in 1 instigate a significant interaction between the 4fxyz orbital of the Gd(III) ion and 3d${{_{x{^{2}}- y{^{2}}}}}$ orbital of the Ni(II) ions, leading to rare and strong antiferromagnetic Ni⋅⋅⋅Gd interactions. Calculations reveal the presence of a strong next-nearest-neighbour Ni⋅⋅⋅Ni antiferromagnetic interaction in complex 1 leading to spin frustration behavior. CASSCF+RASSI-SO calculations performed on complex 2 suggest that the octahedral environment around the Dy(III) ion is neither strong enough to stabilize the mJ |±15/2〉 as the ground state nor able to achieve a large ground-state-first-excited-state gap. The ground-state Kramers doublet for the Dy(III) ion is found to be the mJ |±13/2〉 state with a significant transverse anisotropy, leading to very strong quantum tunneling of Magnetization (QTM). Using the POLY_ANISO program, we have extracted the JNiDy interaction as -1.45 cm(-1) . The strong Ni⋅⋅⋅Dy and next-nearest-neighbour Ni⋅⋅⋅Ni interactions are found to quench the QTM to a certain extent, resulting in zero-field SMM behavior for complex 2. The absence of any ac signals at zero field for the structurally similar [Dy(AlMe4 )3 ] highlights the importance of both the Ni⋅⋅⋅Dy and the Ni⋅⋅⋅Ni interactions in the Magnetization Relaxation of complex 2. To the best of our knowledge, this is the first time that the roles of both the Ni⋅⋅⋅Dy and Ni⋅⋅⋅Ni interactions in Magnetization Relaxation of a {3d-4f} molecular magnet have been established.
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Role of Magnetic Exchange Interactions in the Magnetization Relaxation of {3d–4f} Single‐Molecule Magnets: A Theoretical Perspective
Chemistry (Weinheim an der Bergstrasse Germany), 2015Co-Authors: Saurabh Kumar Singh, Mohammad Faizan Beg, Gopalan RajaramanAbstract:Combined density functional and ab initio calculations are performed on two isomorphous tetranuclear {Ni3 (III) Ln(III) } star-type complexes [Ln=Gd (1), Dy (2)] to shed light on the mechanism of magnetic exchange in 1 and the origin of the slow Magnetization Relaxation in complex 2. DFT calculations correctly reproduce the sign and magnitude of the J values compared to the experiments for complex 1. Acute ∢Ni-O-Gd bond angles present in 1 instigate a significant interaction between the 4fxyz orbital of the Gd(III) ion and 3d${{_{x{^{2}}- y{^{2}}}}}$ orbital of the Ni(II) ions, leading to rare and strong antiferromagnetic Ni⋅⋅⋅Gd interactions. Calculations reveal the presence of a strong next-nearest-neighbour Ni⋅⋅⋅Ni antiferromagnetic interaction in complex 1 leading to spin frustration behavior. CASSCF+RASSI-SO calculations performed on complex 2 suggest that the octahedral environment around the Dy(III) ion is neither strong enough to stabilize the mJ |±15/2〉 as the ground state nor able to achieve a large ground-state-first-excited-state gap. The ground-state Kramers doublet for the Dy(III) ion is found to be the mJ |±13/2〉 state with a significant transverse anisotropy, leading to very strong quantum tunneling of Magnetization (QTM). Using the POLY_ANISO program, we have extracted the JNiDy interaction as -1.45 cm(-1) . The strong Ni⋅⋅⋅Dy and next-nearest-neighbour Ni⋅⋅⋅Ni interactions are found to quench the QTM to a certain extent, resulting in zero-field SMM behavior for complex 2. The absence of any ac signals at zero field for the structurally similar [Dy(AlMe4 )3 ] highlights the importance of both the Ni⋅⋅⋅Dy and the Ni⋅⋅⋅Ni interactions in the Magnetization Relaxation of complex 2. To the best of our knowledge, this is the first time that the roles of both the Ni⋅⋅⋅Dy and Ni⋅⋅⋅Ni interactions in Magnetization Relaxation of a {3d-4f} molecular magnet have been established.