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.

Magnetic-field-controlled spin valve and spin memory based on single-molecule magnets

A single-molecule magnet is a long-sought-after nanoscale component because it can enable us to miniaturize nonvolatile memory storage devices.The signature of a single-molecule magnet is switching between two bistable magnetic ground states under an external magnetic field.Based on this feature,we theoretically investigate a magnetic-fieldcontrolled reversible resistance change active at low temperatures in a molecular magnetic tunnel junction,which consists of a single-molecule magnet sandwiched between a ferromagnetic electrode and a normal metal electrode.Our numerical results demonstrate that the molecular magnetism orientation can be manipulated by magnetic fields to be parallel/antiparallel to the ferromagnetic electrode magnetization.Moreover,different magnetic configurations can be“read out”based on different resistance states or different spin polarization parameters in the current spectrum,even in the absence of a magnetic field.Such an external magnetic field-controlled resistance state switching effect is similar to that in traditional spin valve devices.The difference between the two systems is that one of the ferromagnetic layers in the original device has been replaced by a magnetic molecule.This proposed scheme provides the possibility of better control of the spin freedom of electrons in molecular electrical devices,with potential applications in future high-density nonvolatile memory devices.

Spin-dependent negative differential conductance in transport through single-molecule magnets

Transport properties are theoretically studied through an anisotropy single-molecule magnet symmetrically connected to two identical ferromagnetic leads. It is found that even though in parallel configuration of leads’ magnetizations, the total current still greatly depends on the spin polarization of leads at certain particular bias region, and thus for large polarization a prominent negative differential conductance （NDC） emerges. This originates from the joint effect of single-direction transitions and spin polarization, which removes the symmetry between spin-up and spin-down transitions. The present mechanism of NDC is remarkably different from the previously reported mechanisms. To clarify the physics of the NDC, we further monitored the shot noise spectroscopy and found that the appearance of the NDC is accompanied by the rapid decrease of Fano factor.

The effect of doped ions on single-molecule magnets of the Mn_(12)-Ac family

This paper investigates the single-molecule magnets of pure and Cr/Fe-doped Mn12-Ac. The components of the mixed crystals are identified by AC susceptibility technique. The ground-state spin and anisotropy parameters of doped Mn12-Ac are obtained： （i） MnllCr-Ac （S=19/2, D=0.62K, B=0.0009K, A=63K）, and （ii） Mn11Fe-Ac （S=21/2, D=0.39 K, B=0.001 K, △=55 K）. The single-ion origin of the magnetic anisotropy is discussed.

Transport through artificial single-molecule magnets:Spin-pair state sequential tunneling and Kondo effects

The transport properties of an artificial single-molecule magnet based on a CdTe quantum dot doped with a single Mn＋2 ion（S=5/2） are investigated by the non-equilibrium Green function method.We consider a minimal model where the Mn-hole exchange coupling is strongly anisotropic so that spin-flip is suppressed and the impurity spin S and a hole spin s entering the quantum dot are coupled into spin pair states with（2S＋1） sublevels.In the sequential tunneling regime,the differential conductance exhibits（2S＋1） possible peaks,corresponding to resonance tunneling via（2S＋1） sublevels.At low temperature,Kondo physics dominates transport and（2S＋1） Kondo peaks occur in the local density of states and conductance.These peaks originate from the spin-singlet state formed by the holes in the leads and on the dot via higher-order processes and are related to the parallel and antiparallel spin pair states.

Bias-controlled spin memory and spin injector scheme in the tunneling junction with a single-molecule magnet

A bias-controlled spin-filter and spin memory is theoretically proposed, which consists of the junction with a singlemolecule magnet sandwiched between the nonmagnetic and ferromagnetic(FM) leads. By applying different voltage pulses Vwriteacross the junction, the spin direction of the single-molecule magnet can be controlled to be parallel or anti-parallel to the magnetization of the FM lead, and the spin direction of SMM can be "read out" either by the magneto-resistance or by the spin current with another series of small voltage pulses V_(probe). It is shown that the polarization of the spin current is extremely high(up to 100%) and can be manipulated by the full-electric manner. This device scheme can be compatible with current technologies and has potential applications in high-density memory devices.

A new manganese-based single-molecule magnet with a record-high antiferromagnetic phase transition temperature

We perform both dc and ac magnetic measurements on the single crystal of Mn30（Et-sao）3（C104）（MeOH）3 single- molecule magnet （SMM） when the sample is preserved in air for different durations. We find that, during the oxidation process, the sample develops into another SMM with a smaller anisotropy energy barrier and a stronger antiferromagnetic intermolecular exchange interaction. The antiferromagnetic transition temperature observed at 6.65 K in the new SMM is record-high for the antiferromagnetic phase transition in all the known SMMs. Compared to the original SMM, the only apparent change for the new SMM is that each molecule has lost three methyl groups as revealed by four-circle x-ray diffraction （XRD）, which is thought to be the origin of the stronger antiferromagnetic intermolecular exchange interaction.

All-electric-controlled spin current switching in single-molecule magnet-tunnel junctions

A single-molecule magnet （SMM） coupled to two normal metallic electrodes can both switch spin-up and spin- down electronic currents within two different windows of SMM gate voltage. Such spin current switching in the SMM tunnel junction arises from spin-selected single electron resonant tunneling via the lowest unoccupied molecular orbit of the SMM. Since it is not magnetically controlled but all-electrically controlled, the proposed spin current switching effect may have potential applications in future spintronics.

Enhancing blocking temperature using inverse hydrogen bonds for non-radical bridged dimeric Dy(Ⅲ)single-molecule magnets

Single-molecule magnets(SMMs)are a kind of nanosized magnetic materials that are capable of storing massive bytes of information.Strongly coupling the spin centers in a proper manner is a usual approach to promote the working temperature(or blocking temperature)for SMMs.Electron delocalized radicals have been widely employed to accomplish this job.Here,we show a new manner by using weak but multiple B–H^(δ-)···Dy^(3+)inverse hydrogen bonding(IHB)interactions to control the magnetic couplings in a series of dimeric dysprosiacaborane SMMs.This approach leads to a record high T_(B)^(100s)of 10 K among non-radical bridged dimeric SMMs,which is mainly ascribed to strong ferromagnetic coupling(4.38 cm^(-1))and the proper alignment of the magnetic principle axes of the adjacent dysprosium(Ⅲ)ions.In verifying by theoretical calculations,these results demonstrate that IHB interactions can be used to construct strong axial ferromagnetic coupling and enhancing magnetic blocking temperature for SMMs.

Engineering a high-barrier d-f single-molecule magnet centered with hexagonal bipyramidal Dy(Ⅲ)unit

In the pursuit of high-performance single-molecule magnets(SMMs),incorporating intramolecular magnetic coupling emerges as a pivotal strategy.Among these,d-f SMMs have garnered significant attention due to their remarkable versatility,which lies in their ability to tune coordination environments and facilely substitute metal centers.However,achieving performance-centric d-f SMMs through the synergistic interplay between highly anisotropic f ions and d-f magnetic interactions remains a formidable challenge.While mononuclear hexagonal bipyramidal(D_(6h))Dy^(Ⅲ)SMMs have been successfully isolated,the exploration of d-f SMMs featuring D_(6h)-lanthanide metal centers remains uncharted territory.In this study,we employed planar bipodal ligands in conjunction with“staple-like”axial phenoxide ligands to synthesize the first hexagonal bipyramidal d-f SMM.Remarkably,this compound exhibits alternating-current magnetic susceptibilities peaking up to 68 K with an energy barrier surpassing 1,200 K,thus establishing a new benchmark within the heterometallic d-f SMM landscape inclusive of complexes with diamagnetic d metals and paramagnetic f ions.Notably,the ferromagnetic interaction at the d-f sites engenders oscillating relaxation times contingent on the magnetic field—a characteristic distinct from mononuclear SMMs.These findings shed light on a deliberate design approach for d-f SMMs,emphasizing the cooperative utilization of high-barrier lanthanide modules alongside d ions through magnetic interactions.This synergy significantly enhances and diversifies the magnetic dynamics of these intriguing molecular systems.

Strong Antiferromagnetic Exchange-Coupling Observed in Hydride-Bridged Dimeric Dysprosium(Ⅲ)Single-Molecule Magnet

One dihydride-bridged dimeric Dy(Ⅲ)guanidinate complex,formulated as[{(Me_(3)Si)_(2)NC(NiPr)_(2)}_(2)Dy(μ-H)]_(2)(1Dy),was successfully isolated and the introduction of hydride bridges significantly reduces the intramolecular Dy(Ⅲ)…Dy(Ⅲ)distance to only 3.688(1)Å.To investigate the effect of such a short Dy(Ⅲ)…Dy(Ⅲ)distance on magnetism,we also prepared its dibromide-bridged analogue[{(Me_(3)Si)_(2)NC(NiPr)_(2)}_(2)Dy(μ-Br)]_(2)(2Dy),which has a much longer Dy(Ⅲ)…Dy(Ⅲ)distance of 4.605(4)Å.Surprisingly,2Dy demonstrates much larger effective energy barrier for magnetization reversal(U_(eff))and higher blocking temperature(T_(B)).The worse performance of 1Dy is attributed to the concerted effect of strong antiferromagnetic interactions between Dy(Ⅲ)ions(J_(total)=–2.683 cm^(–1))and the unparallel arrangement of magnetic principle axes of the Dy(Ⅲ)ions for 1Dy.

Anisotropic spin transport and photoresponse characteristics detected by tip movement in magnetic single-molecule junction

Orientation-dependent transport properties induced by anisotropic molecules are enticing in single-molecule junctions.Here,using the first-principles method,we theoretically investigate spin transport properties and photoresponse characteristics in trimesic acid magnetic single-molecule junctions with different molecular adsorption orientations and electrode contact sites.The transport calculations indicate that a single-molecule switch and a significant enhancement of spin transport and photoresponse can be achieved when the molecular adsorption orientation changes from planar geometry to upright geometry.The maximum spin polarization of current and photocurrent in upright molecular junctions exceeds 90%.Moreover,as the Ni tip electrode moves,the tunneling magnetoresistance of upright molecular junctions can be increased to 70%.The analysis of the spin-dependent PDOS elucidates that the spinterfaces between organic molecule and ferromagnetic electrodes are modulated by molecular adsorption orientation,where the molecule in upright molecular junctions yields higher spin polarization.Our theoretical work paves the way for designing spintronic devices and optoelectronic devices with anisotropic functionality base on anisotropic molecules.

A series of heterometallic 3d-4f polyoxometalates as single-molecule magnets

Three sandwich-like[Ln_(2)Fe_(2)(B-α-FeW_9O_(34))_(2)]^(10-) clusters(Ln_(2)Fe_(4),Ln=Dy(1),Ho(2),and Y(3)) were obtained by reacting Na_9[B-α-SbW_9O_(33)],Ln_(2)O_(3),FeCl_(3)·6H_(2)O and KH_(2)PO_(4).The[B-α-FeW_9O_(34)]^(11-) units were formed via the in situ conversion of lacunary polyoxometalates(POM)[B-α-SbW_9O_(33)]^(9-)and the Ln^(3+)ions were generated from the slow dissolution of Ln_(2)O_(3),both of which play important roles in the synthesis of Ln_(2)Fe_(4).Ln_(2)Fe_(4) is the first 3d-4f cluster assembled from d-metal heteroatom-containing POM.The Dy_(2)Fe_(4) cluster exhibits single-molecule magnet properties with an 80 K energy barrier in an optimal DC field.Cyclic voltammetry tests and controlled-potential coulometry experiments show that the polyoxometalate Fe heteroatom in clusters 1-3 is also electrochemically active.

Switching the coordination geometry to enhance erbium(Ⅲ)single-molecule magnets

Two erbium(Ⅲ)complexes[ErCl(OAr^(Ad))_(3)][Na(THF)_(6)](1)and Er(OAr^(Ad))_(3)(2)are successfully prepared by using one variety of"hard"base ligand with large steric hindrance.The coordination geometry around the Er(Ⅲ)site changes from distorted tetrahedral to flat trigonal pyramid geometry in different solvent environment due to the removal of the coordinated chloride.Such an alternation significantly enhances the single-molecule magnet(SMM)behavior and makes the field-induced effective energy barrier(Ueff)arrive at 43(1)cm-1for the latter.Together with theoretical calculations,this study shows that strong equatorial ligand field and high local symmetry are critical to suppress the quantum tunneling of the magnetization(QTM)and achieve high-performance erbium(Ⅲ)based SMMs.

Structures and magnetic relaxation properties of cyclopentadienyl/β-diketonate/trispyrazolylborate hybridized dysprosium single-molecule magnets

The combination of cyclopentadiene,β-diketonate and tripyrazoylborate ligands with dysprosium ion afforded five mononuclear compounds:[(Cp)2Dy(Tp∗)](1Dy),[(Cp)Dy(Tp∗)Cl(THF)](2Dy),[(Cp)Dy(Tp)Cl(THF)](3Dy),[(DBM)Dy(Tp)Cl(THF)](4Dy),[{(Tp)Dy(DBM)_(2)(H_(2)O)}·THF](5Dy)(Cp=cyclopentadiene;Tp∗=hydrotris(3,5-dimethyl-1-pyrazolyl)borate;Tp=hydrotris(1-pyrazolyl)borate;DBM=dibenzoylmethanoate).Magnetic study revealed that 1Dy and 3Dy exhibited typical butterfly-type hysteresis.AC susceptibility study combined with ab initio calculations indicated that the magnetic relaxation behaviors of 1Dy–4Dy were governed by the Orbach and Raman processes under applied DC field.Moreover,3Dy showed two-step magnetic relaxation,which was attributed to the static disordering of the coordinated THF molecule.Magnetic anisotropy analysis indicated that it was the relative strength of the interactions between DyIII and surrounding ligands that determined the orientation of the magnetic easy axis.

Trinuclear Dy(III)Single-Molecule Magnets with Two-Step Relaxation

The reaction of DyCl_(3)·6H_(2)O with a rigid diacylhydrazone ligand(H_(2)L)afforded a trinuclear precursor[Dy_(3)L_(2)Cl_(3)(H_(2)O)_(2)(CH_(3)OH)]Cl_(2)·3CH_(3)OH(1).The replacement of the Cl-ions and the coordinating solvents by the aryloxides ligands(Lx)-yields three trinuclear complexes[Dy_(3)L_(2)(Lx)_(5)]·nsol(x=1,2-naphthol(2);x=2,7-hydroxycoumarin(3);and x=3,phenol(4)).In complexes 2-4,two end Dy^(3+)centers adopt almost identical N_(4)O_(4) coordination sphere of D6h geometry while the central one adopts N_(4)O_(5) coordination sphere in Cs geometry.Magnetic measurements reveal weak antiferromagnetic interactions in the hydrated samples 2e-4e and two-step slow relaxation process under zero dc field with effective energy barriers Ueff of 439 and 91 K,353 and 40 K,466 and 89 K for SR and FR in 2e-4e,respectively.Such dynamic magnetic behaviour for 4 persists in the magnetically diluted sample of 4@Y.Complex 4 possesses the short Dy-O_(aryloxide) bond distance of 2.055(18)Å,and the largest Ueff among the reported linear trinuclear dysprosium complexes.Moreover,the functionalized aryloxides ligands(Lx)-show photoluminescence via intramolecular energy transfer,making 2e-4e luminescent Dy^(3+)SMMs with high energy barriers.

Enhancing single-molecule magnet behavior of linear Co~Ⅱ-Dy~Ⅲ-Co~Ⅱ complex by introducing bulky diamagnetic moiety

Single-molecule magnets （SMMs） are regarded as promising candidates for ultrahigh-density storage, quantum information processing and molecular spintronics. It is a crucial challenge for chemists to modulate magnetic dynamics of SMMs. Here, we successfully synthesized two 3d-4f polynuclear compounds [Co2Dy（TTTTCl）2（MeOH）]NO3.3MeOH （1） and [Co2Dy（TTTTCl）2 （MeOH）][Co（HTTTTCl）]（NO3）z-2.5MeOH＇2H20 （2）, where H3TTTTCl=2,2＇,2＂-（（（nitrilotris（ethane-2,1-diyl）） tris（azanediyl）） tris（methylene））tris-（4-chlorophenol）. On applying the approach by co-crystallization of bulky diamagnetic moiety, the effective energy barrier enhances from 401 K （1） to 536 K （2）, which are both among the highest d-f heterometallic SMMs.

Simultaneous assembly of mononuclear and dinuclear dysprosium(Ⅲ) complexes behaving as single-molecule magnets in a one-pot hydrothermal synthesis

Two dysprosium(Ⅲ) complexes derived from 2,2'-bipyridine-6,6'-dicarboxylic acid(H_2bpdc),[Dy(bpdc)(Hbpdc)]-3H_2O(1) and[Dy_2(bpdc)_3(H_2O)_3]·2.125H_2O(2),were isolated from the same hydrothermal reaction container as different phases.Compound1 is a mononuclear complex with a DyN_4O_4 coordination polyhedron;whereas compound 2 is a dinuclear complex with two types of eight coordinated dy sprosium(Ⅲ) ions,showing DyN_4O_4 and DyN_2O_6 coordination polyhedra,respectively.Remarkably,a new type of(H_2O)_6 supramolecular aggregate exists in the crystal structure of 2.Magnetic investigations revealed that 1 is a field-induced single-ion magnet with an effective energy barrier of 45.6 K,exhibiting two-step magnetic relaxation;while an intramolecular ferromagnetic interaction exists in 2,which is a field-induced single-molecule magnet,displaying two-step magnetic relaxation too,with effective energy barriers of 53.4 and 92.1 K,respectively.

Chelating Guanidinates for Dysprosium(Ⅲ) Single-Molecule Magnets

Two chelating guanidinate-based dysprosium(Ⅲ)complexes,namely the monomeric{(Me_(3)Si)_(2)NC(N^(i)Pr)_(2)}_(2)Dy(μ-CI)_(2)Li(THF)_(2) 1 and the dimeric[{(Me_(3)Si)_(2)NC(N^(i)Pr)_(2)}_(2)Dy(μ-CI)]_(2) 2,have been confirmed to be single-molecule magnets.Moreover,the alteration from 1 to 2 leads to an obvious mitigated quantum tunnelling of magnetization at zero field of the hysteresis loop and much enhanced magnetic relaxation barrier(up to 312 K).5%dilution with the yttrium(Ⅲ)analogue for 2 shows no clear change for the hysteresis,indicating the single-ion nature of the magnetic behavior.

Pressure-induced changes in the magnetic properties of the single crystal of Mn_3 single-molecule magnet

The magnetic measurements of the single crystal of Mn3 single-molecule magnet under high pressure at T=2 K have been performed.We find both the antiferromagnetic intermolecular coupling parameter J and the effective energy barrier to vary compared with the measurements at low pressure.The increase of|J|is estimated to be 12%at 0.7 GPa when compared with that of0 GPa,whereas the effective energy barrier becomes smaller with increasing pressure.Our results demonstrate that the intermolecular interaction of single-molecule magnet can be changed by pressure.Compared with the normal magnetic alloy,the effect of pressure on the magnetic properties of Mn3 is much more prominent,which implies that Mn3 may have great potential in magnetic multifunctional material.