Magnetic Relaxation Processes Research Articles

Enhancement of Effective Energy Barrier and Magnetic Blocking Temperature in Tetraoxolene Radical Coupled Dinuclear Dysprosium Complex.

A well-judged combination of a high axial ligand field and a bridging radical ligand in a dinuclear lanthanide complex provides a single-molecule magnet with a higher effective energy barrier for magnetic relaxation and blocking temperature compared to its non-radical analog due to significant magnetic exchange coupling between radical and Ln(III) ions. In this work, we report two chloranilate (CA) bridged dinuclear dysprosium complexes, [{(bbpen)Dy(μ2-CA)Dy(bbpen)}] (1Dy) and [{(bbpen)Dy(μ2-CA•)Dy(bbpen)}-{CoCp2}+] (2Dy), where 2Dy is the radical bridged Dy-complex obtained via the chemical reduction of bridging CA moiety (H2bbpen = N,N'-bis(2-hydroxybenzyl)-N,N'-bis(2-methylpyridyl)ethylenediamine). The presence of high electronegative phenoxide moiety enhances the axial anisotropy of pseudo-square antiprismatic Dy(III) ions. The diffused spin of radical is efficiently coupled with anisotropic Dy(III) centres and decreases the quantum tunnelling of magnetization (QTM) in the magnetic relaxation process. The magnetic relaxation of 1Dy follows Orbach, Raman, and QTM processes whereas for 2Dy it follows Orbach and Raman Processes. Due to less involvement of the QTM relaxation process, 2Dy shows a higher thermal energy barrier (Ueff = 700 K) and a high blocking temperature (6.7 K), compared to its non-radical analog. Remarkably, the radical coupled 2Dy complex shows the highest energy barrier among the radical bridged Dy(III)-based SMMs to date.

CoII single-ion magnet and its multi-dimensional aggregations: Influence of the structural rigidity on magnetic relaxation process

Two CoII-based complexes, {[Co(dps)2(N3)2]∙H2O}n (1) and [Co(dps)2(N3)2]n (2), show a 1D chain and a 3D network, respectively. The central CoII ions in the complexes have the same coordination environment with the [Co(dps)4(N3)2] unit. Although the differences in crystal parameters are nearly negligible, their magnetic properties are very different. AC susceptibility data show that 1 behaves as a typical field-induced single-ion magnet (SIM) with the out-of-phase (χM'') signals, while 2 shows ac signals of χM'' without peaks even under applied dc filed within our measurement window. Far-IR magneto-spectra (FIRMS) show strong spin-phonon couplings at 0 T in 2, likely making the magnetic relaxation in 2 fast, while the couplings are negligible in 1. Small spin-phonon coupling in 1 likely leads to slower magnetic relaxation, making 1 a SIM. The difference in the properties is due to the structural rigidity of 2 in its 3D network, leading to stronger spin-phonon coupling. Combined high-field EPR (HF-EPR) and FIRMS studies give spin-Hamiltonian parameters, including D = 64.0(9) cm-1, |E| = 15.7(2) cm-1 for 1 and D = 80.0(2) cm-1, |E| = 19.0(1) cm-1 for 2.

Magnetic Relaxation Seen in a Rapidly Evolving Light Bridge in a Sunspot

We report a magnetic relaxation process inside a sunspot associated with the evolution of a transient light bridge (LB). From high-resolution imaging and spectro-polarimetric data taken by the 1.6 m Goode Solar Telescope installed at Big Bear Solar Observatory, we observe the evolutionary process of a rapidly evolving LB. The LB is formed as a result of the strong intrusion of filamentary structures with relatively horizontal fields into the vertical umbral field region. A strong current density is detected along a localized region where the magnetic field topology changes rapidly in the sunspot, especially in the boundary region between the LB and the umbra, and bright jets are observed intermittently and repeatedly in the chromosphere along this region through magnetic reconnection. In the second half of our observation, the horizontal component of the magnetic field diminishes within the LB, and the typical convection structure within the sunspot, which manifests itself as umbral dots, is restored. Our findings provide a comprehensive perspective not only on the evolution of an LB itself but also on its impacts in the neighboring regions, including the chromospheric activity and the change of magnetic energy of a sunspot.

Magnetic boson peak in classical spin glasses

We revisited spin dynamics in archetypical classical spin-glass (SG) systems, such as Cu1−xMnx (x=0.017, 0.034, and 0.067) dilute alloys and iron aluminosilicate glass, using a modern neutron scattering spectrometer with high neutron flux. The former is crystalline, and the latter is amorphous, where their SG state is well separated from magnetically ordered phases. Bose-scaled localized magnetic excitations were observed in both compounds below the spin-freezing temperature (Tf). The spectrum exhibits a maximum at low energy and a broad tail on the high-energy side. The excitation energy tends to be higher for the material with higher Tf. Above Tf, the spectrum considerably changes with temperature, thereby indicating the emergence of the magnetic relaxation process. The magnetic excitation in the SG state has much in common with the boson peak in structural glasses. We consider that the Bose-scaled broad excitation peak is an elementary excitation inherent in disordered systems. Published by the American Physical Society 2024

Theoretical exploration of single-molecule magnetic and single-molecule toroic behaviors in peroxide-bridged double-triangular {MII3LnIII3} (M = Ni, Cu and Zn; Ln = Gd, Tb and Dy) complexes.

Detailed state-of-the-art ab initio and density functional theory (DFT) calculations have been undertaken to understand both Single-Molecule Magnetic (SMM) and Single-Molecule Toroic (SMT) behaviors of fascinating 3d-4f {M3Ln3} triangular complexes having the molecular formula [MII3LnIII3(O2)L3(PyCO2)3](OH)2(ClO4)2·8H2O (with M = Zn; Ln = Dy (1), Tb (2) & Gd (3) and M = Cu; Ln = Dy (4), Tb (5) & Gd (6)) and [Ni3Ln3(H2O)3(mpko)9(O2)(NO3)3](ClO4)·3CH3OH·3CH3CN (Ln = Dy (7), Tb (8), and Gd (9)) [mpkoH = 1-(pyrazin-2-yl)ethanone oxime]. All these complexes possess a peroxide ligand that bridges the {LnIII3} triangle in a μ3-η3:η3 fashion and the oxygen atoms/oxime of co-ligands that connect each MII ion to the {LnIII3} triangle. Through our computational studies, we tried to find the key role of the peroxide bridge and how it affects the SMM and SMT behavior of these complexes. Primarily, ab initio Complete Active Space Self-Consistent Field (CASSCF) SINGLE_ANISO + RASSI-SO + POLY_ANISO calculations were performed on 1, 2, 4, 5, 7, and 8 to study the anisotropic behavior of each Ln(III) ion, to derive the magnetic relaxation mechanism and to calculate the LnIII-LnIII and CuII/NiII-LnIII magnetic coupling constants. DFT calculations were also performed to validate these exchange interactions (J) by computing the GdIII-GdIII and CuII/NiII-GdIII interactions in 3, 6, and 9. Our calculations explained the experimental magnetic relaxation processes and the magnetic exchange interactions for all the complexes, which also strongly imply that the peroxide bridge plays a role in the SMM behavior observed in these systems. On the other hand, this peroxide bridge does not support the SMT behavior. To investigate the effect of bridging ions in {M3Ln3} systems, we modeled a {ZnII3DyIII3} complex (1a) with a hydroxide ion replacing the bridged peroxide ion in complex 1 and considered a hydroxide-bridged {CoIII3DyIII3} complex (10) having the formula [Co3Dy3(OH)4(OOCCMe3)6(teaH)3(H2O)3](NO3)2·H2O. We discovered that as compared to the LoProp charges of the peroxide ion, the greater negative charges on the bridging hydroxide ion reduce quantum tunneling of magnetization (QTM) effects, enabling more desirable SMM characteristics and also leading to good SMT behavior.

AtomAccess: A Predictive Tool for Molecular Design and Its Application to the Targeted Synthesis of Dysprosium Single-Molecule Magnets.

Isolated dysprosocenium cations, [Dy(CpR)2]+ (CpR = substituted cyclopentadienyl), have recently been shown to exhibit superior single-molecule magnet (SMM) properties over closely related complexes with equatorially bound ligands. However, gauging the crossover point at which the CpR substituents are large enough to prevent equatorial ligand binding, but small enough to approach the metal closely and generate strong crystal field splitting has required laborious synthetic optimization. We therefore created the computer program AtomAccess to predict the accessibility of a metal binding site and its ability to accommodate additional ligands. Here, we apply AtomAccess to identify the crossover point for equatorial coordination in [Dy(CpR)2]+ cations in silico and hence predict a cation that is at the cusp of stability without equatorial interactions, viz., [Dy(Cpttt)(Cp*)]+ (Cpttt = C5H2tBu3-1,2,4, Cp* = C5Me5). Upon synthesizing this cation, we found that it crystallizes as either a contact ion-pair, [Dy(Cpttt)(Cp*){Al[OC(CF3)3]4-κ-F}], or separated ion-pair polymorph, [Dy(Cpttt)(Cp*)][Al{OC(CF3)3}4]·C6H6. Upon characterizing these complexes, together with their precursors, yttrium and yttrium-doped analogues, we find that the contact ion-pair shows inferior SMM properties to the separated ion-pair, as expected, due to faster Raman and quantum tunneling of magnetization relaxation processes, while the Orbach region is relatively unaffected. The experimental verification of the predicted crossover point for equatorial coordination in this work tests the limitations of the use of AtomAccess as a predictive tool and also indicates that the application of this type of program shows considerable potential to boost efficiency in exploratory synthetic chemistry.

Fluxionality Modulating the Magnetic Anisotropy in Lanthanoarene [(ηCnRn)2Ln(II/III)] (n = 4-8) Single-Ion Magnets.

Lanthanoarenes have emerged as the best bet for the futuristic application of single-ion magnets in information storage devices. While dysprosocenium molecules with various substituents at the arene ring exhibit a very large blocking temperature, the corresponding Er(III) analogues do not, and this is reversed if the size of the arene ring is eight. Using a combination of ab initio CASSCF and DFT-based molecular dynamics (MD) study, we have explored 25 Dy(III)/Er(III)/Ho(II)/Tb(II)/Dy(II) arene complexes with the ring size varying from 4 to 8 to understand the differences observed and decipher the correlation of structure to the spin dynamics behavior. Among the oxidation state of +2 complexes studied, Tb(II) exhibits the highest barrier, with the Cp-Tb-Cp angle being linear. Further, one of the four-membered arene model studied exhibits a very large barrier of 1442 cm-1, suggesting a potential high-blocking SIM. While bulky substituents at the arene ring help increase the axiality and the CR-Ln-CR angle, this also fetches several agostic C-H···Ln interactions, which injects transverse anisotropy. Furthermore, MD coupled with the CASSCF study reveals that the fluxional behavior of the arene ring generates several rotational conformers that are even accessible at lower temperatures offering a shortcut to the magnetization relaxation process. The importance of structural fluctuations in controlling the magnetic anisotropy by choosing apt metal-ion/ring partners and the corresponding substituents has been highlighted to offer clues to the futuristic SIM design.

Unusual magnetic relaxation in a single-molecule magnet with toroidal magnetic moments

We report the synthesis and characterization of a single-molecule magnet composed of triangular clusters of dysprosium ions. The structural study shows that the symmetry changes from one polar point group (mm2) at room temperature to another polar point group (m) at low temperature. Magnetic studies and theory calculations illustrate that the vortex distribution of magnetic dipoles in the triangular dysprosium clusters forms a toroidal magnetic moment. Interestingly, the analysis of AC magnetic susceptibility reveals the coexistence of three distinct magnetic relaxation processes, corresponding to the Raman, Orbach, and QTM relaxation pathways, respectively. The sum of three modified Debye functions is successfully used to describe the multiple relaxation behavior.

Distinct magnetic relaxation behaviors in nitronyl nitroxide-based cocrystalline supramolecular system with DyIII-O-H⋯O-N hydrogen bond

The self-assembly of Dy(hfac)3·2H2O, Co(hfac)2·2H2O or Mn(hfac)2·2H2O (hfac = hexafiuoroacetylacetonate) with NITPh-triazole radical (NITPh-triazole = 2-[2-(1H-1,2,4-triazol-1-yl)phenyl]-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide) produces two 2p-3d-4f compounds of formula {[Dy(hfac)3(H2O)2][Co2(hfac)4(NITPh-triazole)2]2.CH2Cl2}n (1) and {[Dy(hfac)3(H2O)2][Mn2(hfac)4(NITPh-triazole)2]2}n (2) featuring extraordinary intermolecular hydrogen bonds between coordinated H2O molecules and uncoordinated NO groups linking into a supramolecular one-dimensional chain. Notably, the LnIII-O-H⋯O-N hydrogen bond bridge has been rarely observed in nitronyl nitroxide-metal system. Magnetic performance and heat capacity of both 2p-3d-4f compounds are detected. Interestingly, 1 and 2 both show apparent double peaks of χ′′ signals with two-step magnetic relaxation processes. Furthermore, the effective barrier of 1 is obviously higher than 2. As far as we know, employing unusual intermolecular LnIII-O-H⋯O-N hydrogen bond, it is the first to obtain supramolecular 2p-3d-4f one-dimensional heterospin materials with apparent slow magnetic relaxation and heat capacity behaviors.

Slow magnetic relaxation behavior of a {Dy2} complex based on a large π-conjugated bridging ligand

Binuclear lanthanide single molecule magnets (Ln-SMMs) based on large π-conjugated bridging ligands have shown potential in achieving excellent SMM performance. However, their members are still scarce until now. In this work, a novel binuclear Ln-SMM featuring a large π-conjugated bridging ligand, [Dy2(hfac)6(tpphz)]·CH2Cl2 (1), has been prepared. Its two DyIII centers are chelated and bridged by the large π-conjugated tetrapyrido[3,2-a:2′,3′-c:3′′,2′′-h:2′′′,3′′′-j]phenazine (tpphz) ligand. Three 1,1,1,5,5,5-hexafluoroacetylacetonate (hfac-) ions acting as terminal ligands further complete the square antiprism coordination geometry of each DyIII center. Magnetic measurements revealed that 1 exhibits zero field SMM behavior with a single magnetic relaxation process. The effective energy barrier (Ueff) is 13.79 K. Interestingly, dual relaxation behavior including well-separated slow relaxation (SR) and fast relaxation (FR) processes was further observed when a dc field was applied. It could be ascribed to the different single ion anisotropy of the DyIII centers, as well as a possible contribution of magnetic interactions in the system of 1. The Ueff values for the SR and FR processes are 27.3 and 1.30 K, respectively.

Measuring of water transport selectively along the plant root plasmodesmata using gradient nuclear magnetic resonance with paramagnetic doping

In this study, we measured translational water diffusion selectively along symplast pathway through plasmodesmata in maize roots, and the effective plasmodesmata permeability coefficient (P) was determined using a nuclear magnetic resonance (NMR) spin echo method. Measuring of water transport selectively along the plant root plasmodesmata was achieved with paramagnetic complexes (PCs) of high relaxation efficiency. PCs penetrate into the intercellular space of root tissue, but not into cells, and accelerate the magnetic relaxation processes of intercellular water, thereby excluding the contribution of intercellular water to the registered NMR diffusion echo attenuation. In result, NMR control of translational diffusion can be applied to the signal of the water moving along the symplast pathway through plasmodesmata, where the PCs do not penetrate. Diethylenetriaminepentaacetic acid (GdDTPA), Mn2+-trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid (MnDCTA), and GdCl3 were used as PCs. An increase in the PCs concentration led to a side effect in the form of a varying decrease in diffusive water transport in the roots. The P was determined by extrapolating the concentration dependence to zero concentration of PCs. Among the PCs studied, MnDCTA had the least side effects on the water transport when the concentration dependence was linear. When MnDCTA was used, the P accounted for 30–35% of the total cell water permeability (by transmembrane and symplast pathways). The rate of water flow along the plasmodesmata in the approximation of the piston mode of flow along the linear cell chain was estimated to range from 4.5 × 10−7 to 8.8 × 10−7 m/s.

Porous Mn2+ Magnet with a Pt-Cl Framework: Correlation between Water Vapor Adsorption/Desorption and Slow Magnetic Relaxation.

We report the water adsorption/desorption behavior and dynamic magnetic properties of the Pt-Cl chain complex [{[Pt(en)2 ][PtCl2 (en)2 ]}3 ][{(MnCl5 )Cl3 }2 ] ⋅ 12H2 O (1). Upon heating 1 in a vacuum, we obtained the dehydrated form [{[Pt(en)2 ][PtCl2 (en)2 ]}3 ][{(MnCl5 )Cl3 }2 ] (1DH). The framework structures of 1 and 1DH are identical, and both complexes underwent slow magnetic relaxation. However, the magnetic relaxation times for 1DH were shorter than those for 1, meaning that the dynamic magnetic properties were controlled upon water vapor adsorption/desorption. From detailed analyses of the dynamic magnetic behavior, a phonon-bottleneck effect contributes to the magnetic relaxation processes. We discuss the mechanism for the changes in the magnetic relaxation processes upon dehydration in terms of the heat capacity and thermal conductivity.

Mn-Ln complexes based on azo-salicylaldehyde: Synthesis, structure and magnetic properties

Three Mn-Ln complexes of [MnLn2(TTMSA)4(HTTMSA)2(H2O)6] [Mn(H2O)6]·4H2O (H2TTMSA = 5-azotetrazolyl-3-methoxysalicylaldehyde, Ln = Gd (1), Ho (2), Er (3)) have been synthesized and structurally characterized. The structural characterization reveals that the Mn2+ ion adjusts two mononuclear [LnL3(H2O)2]2 parts into tri-nuclear {[LnL3(H2O)2]2Mn}2− cluster and additional [Mn(H2O)6]2+ just as counter ionto keep electric neutrality of the molecule. The ac susceptibility measurement revels that both complexes of 2 and 3 show slow magnetic relaxation process.

Ferroelectric Single-Molecule Magnet with Toroidal Magnetic Moments.

Materials that coexist magnetic and electric properties on the molecular scale in single‐molecule magnets (SMMs) with peculiar quantum behaviors have promise in molecular electronics and spintronics. Nevertheless, such molecular materials are limited in potentials because their magnetic signal cannot be transformed into an electrical signal through magnetoresistance or Hall effects for their high insulativity. The discovery of an entirely new material, ferroelectric SMMs (FE SMMs) is reported. This FE SMM also shows single‐molecule magnetic behaviors, toroidal magnetic moments, and room‐temperature ferroelectricity. The toroidal moment is formed by a vortex distribution of magnetic dipoles in triangular Dy3 clusters. The analysis of ac magnetic susceptibility reveals the coexistence of three distinct magnetic relaxation processes at low temperatures. The ferroelectricity is introduced by incorporating polar alcohol molecules in the structure, which is confirmed by the X‐ray diffraction and optical second harmonic generation (SHG) measurements. Moreover, the dielectric measurements reveal a ferroelectric‐to‐ferroelectric phase transition around 150 K due to the symmetry change from Pc to Pna21. The coexistence of toroidal moment and ferroelectricity along with quantum magnetism in the rare‐earth single‐molecule magnets yields a unique class of multiferroics.

Effect of site disorder on the resonant microwave absorption in Co2Fe0.5Ti0.5Si Heusler alloy thin films

100 nm Co2Fe0.5Ti0.5Si (CFTS) thin films were grown on Si (100) substrate at different substrate temperatures TS to study the effect of site disorder on the magnetization relaxation processes and magnetic anisotropy in them. To this end, two different ferromagnetic resonance (FMR) techniques have been employed: broad-band (3 – 17 GHz) FMR at a fixed static magnetic field angle in the ‘in-plane’ (IP) sample geometry, and X-band (9.45 GHz) FMR at different polar field-angles, θH, in the ‘out-of-plane’ (OP) sample configuration. Increase in TS reduces the degree of disorder and improves crystalline order. Improvement in crystallinity, in turn, results in the decrease in the strength of magnetocrystalline anisotropy. Irrespective of the degree of disorder present, the OP anisotropy field, Hk⊥, is an order of magnitude higher than the IP counterpart, Hk‖. Out of the CFTS thin films studied, the film (TS500), deposited at TS = 500 °C, has the maximum L21 crystalline order, maximum saturation magnetization (MS = 779 G), and the least values for Hk‖ (5.3 Oe), Hk⊥ (17 Oe), Landé splitting factor, g = 2.02, and the Gilbert damping constant, α=5.5×10-3. These optimum values of MS, g and α, at room temperature, are conducive for spintronics applications. In the OP configuration, the FMR linewidth, ΔH⊥, mainly arises from the intrinsic Landau-Lifshitz-Gilbert damping and extrinsic angular spread of crystallite misorientation. However, the extrinsic two-magnon scattering contribution to ΔH⊥, is appreciable only in the angular range 70° ≤ θH ≤ 110° .

Superparamagnetic Hyperthermia Study with Cobalt Ferrite Nanoparticles Covered with γ-Cyclodextrins by Computer Simulation for Application in Alternative Cancer Therapy.

In this paper, we present a study by computer simulation on superparamagnetic hyperthermia with CoFe2O4 ferrimagnetic nanoparticles coated with biocompatible gamma-cyclodextrins (γ-CDs) to be used in alternative cancer therapy with increased efficacy and non-toxicity. The specific loss power that leads to the heating of nanoparticles in superparamagnetic hyperthermia using CoFe2O4–γ-CDs was analyzed in detail depending on the size of the nanoparticles, the thickness of the γ-CDs layer on the nanoparticle surface, the amplitude and frequency of the alternating magnetic field, and the packing fraction of nanoparticles, in order to find the proper conditions in which the specific loss power is maximal. We found that the maximum specific loss power was determined by the Brown magnetic relaxation processes, and the maximum power obtained was significantly higher than that which would be obtained by the Néel relaxation processes under the same conditions. Moreover, increasing the amplitude of the magnetic field led to a significant decrease in the optimal diameter at which the maximum specific loss power is obtained (e.g., for 500 kHz frequency the optimal diameter decreased from 13.6 nm to 9.8 nm when the field increased from 10 kA/m to 50 kA/m), constituting a major advantage in magnetic hyperthermia for its optimization, in contrast to the known results in the absence of cyclodextrins from the surface of immobilized nanoparticles of CoFe2O4, where the optimal diameter remained practically unchanged at ~6.2 nm.

Design of Dinuclear Lanthanide Complexes from N2O2 Donor Ligand for Single Molecule Magnets: Crystalline Architecture and Slow Magnetic Relaxation Studies

AbstractThree new dinuclear lanthanide complexes [Ln2L2(μ2‐benzoate)2(MeOH)2] ⋅ 4MeOH (H2L=2‐Bis(2‐hydroxybenzyl)aminomethyl]pyridine); Ln=Nd (1), Tb (2), Dy (3)) have been synthesized and structurally characterized by single‐crystal X‐ray diffraction analyses. Compounds 1, 2 and 3 are isomorphous and thus the framework connectivity features are the same for all the three compounds. In the dimeric form of the complexes, each metal centre is octacoordinated with square antiprism (D4d symmetry) geometry, which is completed by a coordinated methanol molecule. In addition, the methanol that present in the structural voids also acts as linkers of paddle‐wheel like complexes. Magnetic properties of the compounds have been investigated in detail using direct‐current and alternating‐current susceptibility measurements. From the analysis of all three complexes, the decrease of susceptibility value at low temperatures is due to the depopulation of Stark sublevels and the existence of intramolecular antiferromagnetic interactions. In addition, complex 3 shows slow relaxation of magnetization behavior, a characteristic feature of single molecule magnets (SMMs). An effective energy barrier value (Ueff) of 38.87 K and relaxation time (τ0) of 1.665×10−7 s for the magnetic relaxation process was obtained for 3. Solid state luminescence spectra for complex 2 show characteristic green emission peaks at 543 nm region having potential for applications in the solid state as light emitting diodes and photoluminescent materials.

Slow-Relaxation Behavior of a Mononuclear Co(II) Complex Featuring Long Axial Co-O Bond.

Co(II) mononuclear complex with different coordination geometry would display various of field-induced single-ion magnet (SIM) behaviors. Here, we identify a field-induced single-ion magnet in a mononuclear complex Co(H2DPA)2·H2O (H2DPA = 2,6-pyridine-dicarboxylic acid) by the hydrothermal method. The long axial Co-O coordination bond (Co1‧‧‧O3) can be formed by Co1 and O3. Therefore, Co(II) ion is six-coordinated in a distorted elongated octahedron. AC magnetization susceptibilities show that the effective energy barrier is up to 43.28 K. This is much larger than most mononuclear Co(II). The distorted elongated octahedron caused by the axial Co-O coordination bond is responsible for the high effective energy barrier. The distribution of electron density in Co1 and O3 atoms in the long axial bond would influence the magnetic relaxation process in turn. Our work deepens the relationship between the effective energy barrier and the weak change of ligand field by long axial bonds, which would facilitate constructing SIM with high energy temperature.

Magnetic nanoparticle relaxation processes key for medical imaging techniques

Separating Brownian and Néel relaxation mechanisms by timescale using advanced technology.

A nonsymmetric Dy2 single-molecule magnet with two relaxation processes triggered by an external magnetic field: a theoretical and integrated EPR study of the role of magnetic-site dilution.

The 1 : 2 reaction between Dy(O2CMe)3·4H2O and 1-acetyl-2-napthol (LH) in MeOH has provided access to the complex [Dy2L6(MeOH)]·MeOH (1·MeOH) in a good yield. The structures of the isomorphous complex 1·MeOH and its doped diamagnetic yttrium analogue [Dy0.14Y1.86L6(MeOH)]·MeOH (Dy@Y2) have been determined by single-crystal X-ray crystallography and characterized based on elemental analyses, IR spectra, and powder X-ray patterns. Combined dc and ac magnetic susceptibility and the magnetization data for 1 suggest that this complex shows slow magnetic relaxation. Under a 0 Oe dc field, a single relaxation mechanism is seen while two magnetization relaxation processes are evident under a 1500 G external magnetic field. The fit to the Arrhenius law has been performed using the 1.8-10 K ac data, affording an effective barrier for the magnetization reversal of 13 K and 7 K under the external dc field. Theoretical studies have been performed using ab initio and density functional methodologies to understand the electronic structure and the magnetic relaxation dynamics resulting from the single DyIII ion as well as from the dinuclear exchange-coupled states. Rich powder EPR spectra at the X-band and Q-band were obtained from Dy@Y2, as well as from the 1·MeOH dimer, while simulation studies revealed the ferromagnetic nature of the interaction between the DyIII ions in accordance with theoretical studies.