Magnetic Blocking Temperature Research Articles

Exploring the Magnetism of C5/C2B3 Heteroleptic Organolanthanide Sandwiches

Comprehensive SummaryTwo families of cyclopentadienyl (Cp)/carboranyl heteroleptic sandwiched organolanthanide complexes, namely [Ln{η5:σ‐Me2C(C5H4)(C2B10H10)}2][Li(DME)3] (1Ln, Ln = Tb, Dy, Ho, Er) and [2‐THF‐2'‐(μ2‐Cl)Li(THF)3‐2,2'‐Ln(nido‐1,7‐C2B9H11)Cp*] (2Dy), were synthesized. Family of 1Ln has been proposed based on the mixing‐ligands idea by linking Cp and nido‐dicarborllide. However, the carborane cage of [Me2C(C5H4)(C2B10H10)]2− deprotons and forms a mono‐C− anion rather than deboron to form dicarborllide dianion. Hence, the family of 1Ln features a dysprosocenium skeleton with extra two coordination of C− anions of carborllides. Such coordination geometry is more like a tetrahedron if abstracting the centroids of two coordinated Cp rings. In this cubic‐type geometry, no significant magnetic axiality is presented; only 1Dy and 1Tb show field‐induced slow magnetic relaxation behavior below 10 K. Inspired by 1Ln, the free pentamethylcyclopentadienyl (Cp*−) and nido‐dicarborllide ligands are used to sandwich central Dy3+ ion, achieving heteroleptic complex 2Dy. The bending angle by linking the centroid of Cp*−, Dy3+ and C2B32− in 2Dy is increased to 132.8(1)°. As such, the effective energy barrier for magnetic reversal (Ueff) and magnetic blocking temperature TB (ZFC) are both increased (Ueff = 616(10) K; TB = 6 K). The effort of further enhancing Ueff and TB in such heteroleptic organolanthanide sandwiches should rely on keeping increasing the ligand axiality.

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.

Short Didysprosium Covalent Bond Enables High Magnetization Blocking Temperature of a Direct 4f-4f Coupled Dinuclear Single-Molecule Magnet.

Coupling two magnetic anisotropic lanthanide ions via a direct covalent bond is an effective way to realize high magnetization blocking temperature of single-molecule magnets (SMMs) by suppressing quantum tunneling of magnetization (QTM), whereas so far only single-electron lanthanide-lanthanide bonds with relatively large bond distances are stabilized in which coupling between lanthanide and the single electron dominates over weak direct 4f-4f coupling. Herein, we report for the first time synthesis of short Dy(II)-Dy(II) single bond (3.61 Å) confined inside a carbon cage in the form of an endohedral metallofullerene Dy2@C82. Such a direct Dy(II)-Dy(II) covalent bond renders a strong Dy-Dy antiferromagnetic coupling that effectively quenches QTM at zero magnetic field, thus opening up magnetic hysteresis up to 25 K using a field sweep rate of 25 Oe/s, concomitant with a high 100 s magnetization blocking temperature (TB,100s) of 27.2 K.

Incidence of the Brownian Relaxation Process on the Magnetic Properties of Ferrofluids.

Ferrofluids containing magnetic nanoparticles represent a special class of magnetic materials due to the added freedom of particle tumbling in the fluids. We studied this process, known as Brownian relaxation, and its effect on the magnetic properties of ferrofluids with controlled magnetite nanoparticle sizes. For small nanoparticles (below 10 nm diameter), the Néel process is expected to dominate the magnetic response, whereas for larger particles, Brownian relaxation becomes important. Temperature- and magnetic-field-dependent magnetization studies, differential scanning calorimetry, and AC susceptibility measurements were carried out for 6 and 13.5 nm diameter magnetite nanoparticles suspended in water. We identify clear fingerprints of Brownian relaxation for the sample of large-diameter nanoparticles as both magnetic and thermal hysteresis develop at the water freezing temperature, whereas the samples of small-diameter nanoparticles remain hysteresis-free down to the magnetic blocking temperature. This is supported by the temperature-dependent AC susceptibility measurements: above 273 K, the data show a low-frequency Debye peak, which is characteristic of Brownian relaxation. This peak vanishes below 273 K.

Substituted fullerenes as a promising capping ligand towards stabilization of exohedral Dy(III) based single-ion magnets: a theoretical study.

Organometallic dysprosocenium-based molecular magnets are the forefront runners in offering giant magnetic anisotropy and blocking temperatures close to the boiling point of liquid nitrogen. Attaining linearity in the organometallic dysprosocenium complexes is the key to generating giant magnetic anisotropy and blocking barriers. In the present study, we have unravelled the coordination ability of the substituted fullerene (C55X5)- (where X = CCH3, B, and N) generated by fencing around the five-membered ring of fullerene towards stabilizing a new family of exohedral dysprosium organometallic complexes showcasing giant magnetic anisotropy and blockade barriers. Eight exohedral mononuclear dysprosium organometallic complexes, namely [Dy(η5-C55X5)(η4-C4H4)] (1), [Dy(η5-C55X5)(η5-Cp)]+ (2), [Dy(η5-C55X5)(η5-Cp*)]+ (3), [Dy(η5-C55X5)(η6-C6H6)]2+ (4), [Dy(η5-C55X5)(η8-C8H8)] (5), [Dy(η5-C55X5)2]+ (6) (where X = CCH3), [Dy(η5-C55B5)2]+ (7) and [Dy(η5-C55N5)2]+ (8), were studied using scalar relativistic density functional theory (SR-DFT) and the complete active space self-consistent field (CASSCF) methodology to shed light on the structure, stability, bonding and single-ion magnetic properties. SR-DFT calculations predict complexes 1-8 to be highly stable, with a strictly linear geometry around the Dy(III) ion in complexes 6-8. Energy Decomposition Analysis (EDA) predicts the following order for interaction energy (ΔEint value): 5 > 1 > 2 ≈ 3 > 6 > 7 > 8 > 4, with sizable 4f-ligand covalency in all the complexes. CASSCF calculations on complexes 1-8 predict stabilization of mJ |±15/2〉 as the ground state for all the complexes except for 5, with the following trend in the Ucal values: 6 (1573 cm-1) ≈ 3 (1569 cm-1) > 1 (1538 cm-1) > 8 (1347 cm-1) > 2 (1305 cm-1) > 7 (1284 cm-1) > 4 (1125 cm-1) > 5 (108 cm-1). Ab initio ligand field theory (AILFT) analysis provides a rationale for Ucal ordering, where π-type 4f-ligand interactions in complexes 1-4 and 6-8 offer giant barrier height while the large (C8H8)2- rings generate δ-type interaction in 5, which diminishes the axiality in the ligand field. Our detailed finding suggests that the exohedral organometallic dysprosocenium complexes are more linear compared to bent [DyCp*2]+ cations and display a giant barrier height exceeding 1500 cm-1 with negligible quantum tunnelling of magnetization (QTM) - a new approach to design highly anisotropic dysprosium organometallic complexes.

Halide mediated modulation of magnetic interaction and anisotropy in dimeric Co(II) complexes.

The burgeoning interest in the field of molecular magnetism is to perceive the high magnetic anisotropy in different geometries of metal complexes and hence to draw a magneto-structural correlation. Despite a handful of examples to exemplify the magnetic anisotropy in various coordination geometries of mononuclear complexes, the magnetic anisotropies for two different coordination geometries are underexplored. Employing an appropriate synthetic strategy utilizing the ligand LH2 [2,2'-{(1E,1'E)-pyridine2,6-diyl-bis(methaneylylidine)}-bis(azaneylylidine)diphenol] and cobalt halide salts in a 1 : 2 stoichiometric ratio in the presence of triethylamine allowed us to report a new family of dinuclear cobalt complexes [CoII2X2(L)(P)(Q)]·S with varying terminal halides [X = Cl, P = CH3CN, Q = H2O, S = H2O (1), X = Br, P = CH3CN, Q = H2O, S = H2O (2), X = I, P = CH3CN, and Q = CH3CN (3)]. All these complexes are characterized through single crystal X-ray crystallography, which reveals their crystallization in the monoclinic system P21/n space group with nearly identical structural features. These complexes share vital components, including Co(II) centers, a fully deprotonated ligand [L]2-, halide ions, and solvent molecules. The [L]2- ligand contains two Co(II) centers, where phenolate oxygen atoms bridge the Co(II) centers, forming a Co2O2 four-membered ring. Co1 demonstrates a distorted pentagonal-bipyramidal geometry with axial positions for solvent molecules, while Co2 displays a distorted tetrahedral geometry involving phenolate oxygen atoms and halide ions. Temperature-dependent dc magnetic susceptibility measurements were conducted on 1-3 within a range of 2 to 300 K at 1 kOe. The χmT vs. T plots exhibit similar trends, with χmT values at 300 K higher than the spin-only value, signifying a significant orbital contribution. As the temperature decreases, χmT decreases smoothly in all the complexes; however, no clear saturation at low temperatures is observed. Field-dependent magnetization measurements indicate a rapid increase below 20 kOe, with no hysteresis and a low magnetic blocking temperature. DFT and CASSCF/NEVPT2 theoretical calculations were performed to perceive the magnetic interaction and single-ion anisotropies of Co(II) ions in various ligand-field environments.

A hard molecular nanomagnet from confined paramagnetic 3d-4f spins inside a fullerene cage

Reducing inter-spin distance can enhance magnetic interactions and allow for the realization of outstanding magnetic properties. However, achieving reduced distances is technically challenging. Here, we construct a 3d-4f metal cluster (Dy2VN) inside a C80 cage, affording a heretofore unseen metallofullerene containing both paramagnetic 3d and 4f metal ions. The significantly suppressed 3d-4f (Dy-V) distances, due to the unique cage confinement effect, were observed by crystallographic and theoretical analysis of Dy2VN@Ih(7)-C80. These reduced distances result in an enhanced magnetic coupling (Jtotal, Dy-V = 53.30 cm−1; Jtotal, Dy-Dy = −6.25 cm−1), leading to a high magnetic blocking temperature compared to reported 3d-4f single-molecule magnets and strong coercive field of 2.73 Tesla. Our work presents a new class of single-molecule magnets with both paramagnetic 3d and 4f metals confined in a fullerene cage, offering superior and tunable magnetic properties due to the unique cage confinement effect and the diverse composition of the entrapped magnetic core.

Nd─Nd Bond in Ih and D5h Cage Isomers of Nd2 @C80 Stabilized by Electrophilic CF3 Addition.

Synthesis of molecular compounds with metal-metal bonds between 4f elements is recognized as one of the fascinating milestones in lanthanide metallochemistry. The main focus of such studies is on heavy lanthanides due to the interest in their magnetism, while bonding between light lanthanides remains unexplored. In this work, the Nd─Nd bonding in Nd-dimetallofullerenes as a case study of metal-metal bonding between early lanthanides is demonstrated. Combined experimental and computational study proves that pristine Nd2 @C80 has an open shell structure with a single electron occupying the Nd─Nd bonding orbital. Nd2 @C80 is stabilized by a one-electron reduction and further by the electrophilic CF3 addition to [Nd2 @C80 ]- . Single-crystal X-ray diffraction reveals the formation of two Nd2 @C80 (CF3 ) isomers with D5h -C80 and Ih -C80 carbon cages, both featuring a single-electron Nd─Nd bond with the length of 3.78-3.79 Å. The mutual influence of the exohedral CF3 group and endohedral metal dimer in determining the molecular structure of the adducts is analyzed. Unlike Tb or Dy analogs, which are strong single-molecule magnets with high blocking temperature of magnetization, the slow relaxation of magnetization in Nd2 @Ih -C80 (CF3 ) is detectable via out-of-phase magnetic susceptibility only below 3 K and in the presence of magnetic field.

Theoretical Magnetic Relaxation and Spin-Phonon Coupling Study in a Series of Molecular Engineering Designed Bridged Dysprosocenium Analogues.

A detailed computational study of hypothetical sandwich dysprosium double-decker complexes, bridged by various numbers of aliphatic linkers, was performed to evaluate the effect of the structural modifications on their ground-state magnetic sublevels and assess their potential as candidates for single-molecule magnets (SMMs). The molecular structures of seven complexes were optimized using the TPSSh functional, and the electronic structure and magnetic properties were investigated using the complete active space self-consistent field method (CASSCF). Estimates of the magnetic moment blocking barrier (Ueff) and blocking temperatures (TB) are reported. In addition, a new method based on computed derivatives of effective demagnetization barriers Ueff with respect to vibrational normal modes was introduced and applied to evaluate the impact of spin-phonon coupling on the SMM properties. On the basis of the computed parameters, we have identified promising candidates with properties superior to those of the existing single-molecule magnets.

Magnetic susceptibility of a ternary Ising nanoisland

We investigate magnetic properties of a ternary ( 1 / 2 , 1, 3 / 2 ) bilayer Ising nanoisland with an 18-site quadratic structure. By employing exact enumeration, we study the effects of crystal fields, exchange couplings and thermal fluctuations on the magnetic susceptibility and blocking temperature. As a result, we find several scenarios in which a double peak structure in the thermal dependence of the magnetic susceptibility can be observed. In particular, the competition between core–shell antiferromagnetic interactions and the external magnetic field can drive an additional low-temperature maximum in the magnetic susceptibility. In addition, the competition between core–shell couplings and a strong crystal field in the core spins can also provide a scenario in which the magnetic susceptibility shows two maximum. From the magnetic susceptibility maximum at higher temperatures, we estimate the blocking temperature. Surprisingly, we note that an increase in the absolute value of the exchange couplings can reduce the blocking temperature. Moreover, our findings suggest that the mechanism driving the double maxima in the magnetic susceptibility also provides a context in which the increase in the strength of the exchange coupling can lead to a reduction in the blocking temperature. Therefore, our results allow us to describe different scenarios in which double-peak structures in the magnetic susceptibility of nanoparticles can be spotted, also suggesting that these scenarios can favor a reduced blocking temperature. • Magnetism of a mixed-spin (1/2,1,3/2) nanoisland with core–shell structure has been investigated. • Effects of crystal fields and exchange couplings are evaluated. • Thermal dependence of magnetic susceptibility shows a double-peak structure. • Blocking temperature shows non-monotonic dependence on the core–shell couplings.

Structure and properties of Co-=SUB=-x-=/SUB=-Mn-=SUB=-1-x-=/SUB=-Fe-=SUB=-2-=/SUB=-O-=SUB=-4-=/SUB=- nanoparticles depending on the amount of Co ions (0≤ x≤ 1.0)

The properties of magnetic nanoparticles (MNPs) of spinel ferrites CoxMn1-xFe2O4 (at x=0.0; 0.2; 0.3; 0.4; 0.5; 0.6; 0.8; 1.0) synthesized by chemical co-precipitation method have been studied. The studies of the synthesized CoxMn1-xFe2O4 MNPs were carried out using X-ray diffraction (XRD), Raman scattering and Mossbauer spectroscopy. The results of XRD, Raman and Mossbaur studies indicate that the obtained CoxMn1-xFe2O4 MNPs are single-phase. It was established from XRD measurements that the average size of CoxMn1-xFe2O4 crystallites is 34.86 nm for MnFe2O4 (x=0) and decreases to 14.99 nm for CoFe2O4 (x=1.0) with increasing Co ions concentration. An analysis of the Mossbaur spectra showed that the average crystallite size varies from 25 nm for MnFe2O4 (x=0) to 12 nm for CoFe2O4 (x=1.0). On the Raman spectra of CoxMn1-xFe2O4 MNPs, in the region of ~620 cm-1, splitting of the A1g line is observed, which means that the studied MNPs have a reverse spinel structure. The intensity ratio of the A1g (1) and A1g (2) peaks indicates a significant redistribution of the Co2+ and Fe3+ cations between tetra- and octahedralpositions in MNPs of the CoxMn1-xFe2O4 ferrite, which is confirmed by Mossbauer data. Mossbaur spectroscopy data indicate that the synthesized CoxMn1-xFe2O4 MNPs consist of large particles with magnetic ordering and small particles in the paramagnetic phase. With an increase in the concentration of Mn ions, the proportion of fine particles increases, which leads to a decrease in the magnetic blocking temperature. The saturation magnetization of MNPs at x=0.2 (Co0.2Mn0.8Fe2O4) is 57.41 emu/g and this sample, as was found in [V. Narayanaswamy, I.A. Al-Omari, A.S. Kamzin, B. Issa, H.O. Tekin, H. Khourshid, H. Kumar, A. Mallya, S. Sambasivam, I.M. Obaidat. Nanomaterials 11, 1231 (2021)] has the highest specific absorption rate. As shown by Mossbauer studies, this is due to the fact that these particles are in a superparamagnetic state and the magnetic blocking temperature of these MNPs is in the region of ~315 K, which is most suitable for the treatment of malignant tumors by magnetic hyperthermia. Thus, the synthesized CoxMn1-xFe2O4 MNPs are promising for biomedical applications. Keywords: spinel ferrites CoxMn1-xFe2O4, magnetic structure, superparamagnetism, Mossbauer spectroscopy, materials for biomedicine.

AC Susceptibility Studies under DC Fields in Superspinglass Nanomaghemite-Multiwall Carbon Nanotube Hybrid

Magnetic properties of maghemite (γ-Fe2O3) nanoparticles grown on activated multiwall carbon nanotubes have been studied by alternating current (AC) magnetic susceptibility experiments performed under different temperatures, frequencies, and applied magnetic fields. Transmission electron images have suggested that the γ-Fe2O3 nanoparticles are not isolated and have an average size of 9 nm, but with a relatively broad size distribution. The activation energies of these 9 nm γ-Fe2O3 nanoparticles, determined from the generalized Vogel–Fulcher relation, are reduced upon increasing the direct current (DC) field magnitude. The large activation energy values have indicated the formation of a superspinglass state in the γ-Fe2O3 nanoparticle ensemble, which were not observed for pure γ-Fe2O3 nanoparticles, concluding that the multiwall carbon nanotubes favored the appearance of highly concentrated magnetic regions and hence the formation of superspinglass state. Magnetic relaxation studies, using Argand diagrams recorded for DC probe fields (<20 kOe) below the magnetic blocking temperature at 100 and 10 K, have revealed the presence of more than one relaxation process. The behavior of the ensemble of γ-Fe2O3 nanoparticles can be related to the superspinglass state and is also supported by Almeida–Thouless plots.

Size-dependent catalytic effect of magnetite nanoparticles in the synthesis of tunable magnetic polyaniline nanocomposites

Nanocomposites comprising magnetic nanoparticles (NPs) embedded in an organic conducting polymer are promising materials that may allow one to exploit synergic effects between the electrically conducting and the magnetically permeable components. Having already shown that magnetite NPs can be conveniently used as a catalyst for the oxidative polymerization of the aniline dimer resulting in NPs embedded in the final composite and how to modulate the magnetic coercivity of the composites, we now turn to investigate how the size of magnetite NPs affects the polymerization and the properties of the final composite. Magnetite NPs of diameter 2.3, 10, and 27 nm turned out to be effective catalysts with cheap oxidants such as H2O2 and O2. Yield data show that the rate-determining step occurs on the NP surface. Extensive characterization shows that the NPs are well-dispersed in the composite with no significant morphological change. The static magnetic properties of the composites are widely different, e.g., the magnetic blocking temperature shifts from 290 K for 27 nm NPs to 54 K for 10 nm NPs, while composites with 2.3 nm NPs are virtually unblocked down to 5 K. The dynamic electromagnetic behavior studied up to the microwave range only shows energy absorptions associated with the ferromagnetic resonance, at frequencies around 1 GHz.

Magnetic Hysteresis at 10 K in Single Molecule Magnet Self-Assembled on Gold.

Tremendous progress in the development of single molecule magnets (SMMs) raises the question of their device integration. On this route, understanding the properties of low‐dimensional assemblies of SMMs, in particular in contact with electrodes, is a necessary but difficult step. Here, it is shown that fullerene SMM self‐assembled on metal substrate from solution retains magnetic hysteresis up to 10 K. Fullerene‐SMM DySc2N@C80 and Dy2ScN@C80 are derivatized to introduce a thioacetate group, which is used to graft SMMs on gold. Magnetic properties of grafted SMMs are studied by X‐ray magnetic circular dichroism and compared to the films of nonderivatized fullerenes prepared by sublimation. In self‐assembled films, the magnetic moments of the Dy ions are preferentially aligned parallel to the surface, which is different from the disordered orientation of endohedral clusters in nonfunctionalized fullerenes. Whereas chemical derivatization reduces the blocking temperature of magnetization and narrows the hysteresis of Dy2ScN@C80, for DySc2N@C80 equally broad hysteresis is observed as in the fullerene multilayer. Magnetic bistability in the DySc2N@C80 grafted on gold is sustained up to 10 K. This study demonstrates that self‐assembly of fullerene‐SMM derivatives offers a facile solution‐based procedure for the preparation of functional magnetic sub‐monolayers with excellent SMM performance.

Optimization of structure-property relationships in nickel ferrite nanoparticles annealed at different temperature

In this report, a detail analysis of the impact of annealing temperature on the structural, elastic, morphological, optical, and magnetic behavior of NiFe2O4 nanoparticles prepared by the citrate sol-gel method is presented. Analyzing the XRD patterns by the Rietveld method confirms that all the annealed samples have been crystallized to cubic spinel structure belonging to Fd3−m space group with a single phase. Rietveld analysis demonstrates the change in structural and microstructural parameters and movement of cations from tetrahedral to octahedral sites and vice-versa upon annealing. The quantitative estimation of Ni2+ & Ni3+ and Fe2+ & Fe3+ has been carried out using XPS analysis. Decreases in peak broadening and shift of five Raman active peaks towards higher frequency upon annealing have been analyzed using the phonon confinement model. The variation in elastic parameters with annealing temperature has been assessed by FTIR analysis. The UV analysis reveals the increase of the optical energy band gap and the decrease of Urbach energy with annealing temperature enhancement. A noticeable sharp absorption band at 748 nm in UV spectra is attributed to A32g(3F)→T31g(3F) electronic transition. Room temperature magnetic hysteresis loops exhibit an increase of saturation magnetization upon annealing which is discussed with reference to finite size effects and disorderly surface spins. The estimated value of magnetocrystalline anisotropy constant by Law of Approach to saturation (LAS) theory as well as coercivity value elucidates the annealing effect in changing the magnetic single domain state of the particle to a multidomain state. Analysis of ZFC and FC magnetization curve measured at 100 Oe in the temperature range 400 K–60 K reveals the significant impact of annealing temperature on magnetic anisotropy, inter-particle interaction, and blocking temperature. Exploring the magnetic hysteresis loop measured in the temperature range 60–400 K over field strength of ± 3 T demonstrates the significant role of annealing on magnetic exchange interaction. Temperature dependent behavior of saturation magnetization and coercivity has been analyzed using modified Bloch's law and Kneller's relation. The magnetic heating efficiency examined by the induction heating system reveals that the sample has enough potential for hyperthermia application.

Shining New Light on Multifunctional Lanthanide Single-Molecule Magnets.

Single-molecule magnets (SMMs) are at the forefront of new technological advances in quantum information processing and spintronics. Despite the recent impressive breakthroughs in extending the magnetic blocking temperatures beyond liquid-nitrogen temperatures, significant challenges await in terms of integrating and addressing such compounds in devices. With this ultimate goal in mind, the design of multifunctional SMMs not only allows to imbue molecules of interest with specific properties that would allow for in situ monitoring of the SMM operation in real time, but can also provide critical insights into our understanding of the magnetic behaviour. In this Review, we highlight how magnetism and luminescence can be harmoniously combined within single molecules to achieve these objectives. The key design principles to attain the simultaneous combination of photoluminescence and slow relaxation of the magnetization are discussed, along with an outlook on how such molecules could be beneficial for emerging next-generation spintronics devices.

Single-Molecule Magnets DyM2 N@C80 and Dy2 MN@C80 (M=Sc, Lu): The Impact of Diamagnetic Metals on Dy3+ Magnetic Anisotropy, Dy⋅⋅⋅Dy Coupling, and Mixing of Molecular and Lattice Vibrations.

The substitution of scandium in fullerene single‐molecule magnets (SMMs) DySc2N@C80 and Dy2ScN@C80 by lutetium has been studied to explore the influence of the diamagnetic metal on the SMM performance of dysprosium nitride clusterfullerenes. The use of lutetium led to an improved SMM performance of DyLu2N@C80, which shows a higher blocking temperature of magnetization (T B=9.5 K), longer relaxation times, and broader hysteresis than DySc2N@C80 (T B=6.9 K). At the same time, Dy2LuN@C80 was found to have a similar blocking temperature of magnetization to Dy2ScN@C80 (T B=8 K), but substantially different interactions between the magnetic moments of the dysprosium ions in the Dy2MN clusters. Surprisingly, although the intramolecular dipolar interactions in Dy2LuN@C80 and Dy2ScN@C80 are of similar strength, the exchange interactions in Dy2LuN@C80 are close to zero. Analysis of the low‐frequency molecular and lattice vibrations showed strong mixing of the lattice modes and endohedral cluster librations in k‐space. This mixing simplifies the spin–lattice relaxation by conserving the momentum during the spin flip and helping to distribute the moment and energy further into the lattice.

Dy2@C79N: a new member of dimetalloazafullerenes with strong single molecular magnetism.

Enhancing the exchange interaction between magnetic ions is a long-term target in molecular magnetism. Endohedral metallofullerenes (EMFs) provide a possibility for achieving such a goal by imprisoning multiple magnetic centers inside the confined inner space of a fullerene cage. Here, we report a new member of dimetallic azafullerene Dy2@C79N via crystallographic determination for the first time. Magnetic studies indicate that the strong ferromagnetic coupling between lanthanide ions and unpaired electrons enables Dy2@C79N to be a favorable SMM with large energy barrier of U = 669 K and observable hysteresis loops below 24 K.

High blocking temperatures for DyScS endohedral fullerene single-molecule magnets.

Dy-based single-molecule magnets (SMMs) are of great interest due to their ability to exhibit very large thermal barriers to relaxation and therefore high blocking temperatures. One interesting line of investigation is Dy-encapsulating endohedral clusterfullerenes, in which a carbon cage protects magnetic Dy3+ ions against decoherence by environmental noise and allows for the stabilization of bonding and magnetic interactions that would be difficult to achieve in other molecular architectures. Recent studies of such materials have focused on clusters with two Dy atoms, since ferromagnetic exchange between Dy atoms is known to reduce the rate of magnetic relaxation via quantum tunneling. Here, two new dysprosium-containing mixed-metallic sulfide clusterfullerenes, DyScS@Cs(6)–C82 and DyScS@C3v(8)–C82, have been successfully synthesized, isolated and characterized by mass spectrometry, Vis-NIR, cyclic voltammetry, single crystal X-ray diffractometry, and magnetic measurements. Crystallographic analyses show that the conformation of the encapsulated cluster inside the fullerene cages is notably different than in the Dy2X@Cs(6)–C82 and Dy2X@C3v(8)–C82 (X = S, O) analogues. Remarkably, both isomers of DyScS@C82 show open magnetic hysteresis and slow magnetic relaxation, even at zero field. Their magnetic blocking temperatures are around 7.3 K, which are among the highest values reported for clusterfullerene SMMs. The SMM properties of DyScS@C82 far outperform those of the dilanthanide analogues Dy2S@C82, in contrast to the trend observed for carbide and nitride Dy clusterfullerenes.

Magnetic and Electrocatalytic Properties of Nanoscale Cobalt Boride, Co3B.

The use of low-temperature solution synthesis followed by a brief annealing step allows metastable single-phase Co3B nanoparticles to be obtained, with sizes ranging from 11 to 22 nm. The particles are ferromagnetic with a saturation magnetization of 91 A m2 kg-1 (corresponding to 1.02 μB/Co) and a coercive field of 0.14 T at 5 K, retaining the semihard magnetic properties of bulk Co3B. They display a magnetic blocking temperature of 695 K and a Curie temperature near 710 K, but the measurement of these high-temperature properties was complicated by decomposition of the particles during heating in the magnetometer. Additionally, the nanoparticles of Co3B were investigated as an electrocatalyst in the oxygen evolution reaction and showed a low onset potential of 1.55 V vs RHE. XPS measurements were performed before and after the electrocatalytic measurements to study the surface of the catalyst, to pinpoint what appear to be the active surface species.