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valve devices.The difference between the two systems is that one of the ferromagnetic layers in the original device has been replaced by a magnetic molecule.This proposed scheme provides the possibility of better control of the spin freedom of electrons in molecular electrical devices,with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.

Enhanced conductivity and weakened magnetism in Pb-doped Sr_(2)IrO_(4)

Group IV element Pb has been selected as the dopant to dope at the Sr site of Sr_(2)IrO_(4). It is exciting to find that the single-phase crystal structure could be maintained with a high Pb doping level of up to x=0.3 in Sr_(2-x)Pb_(x)IrO_(4). The mapping data obtained from energy-dispersive x-ray spectroscopy analyses give solid evidence that the Pb ions are uniformly distributed in the Sr_(2)IrO_(4) matrix. The incorporation of Pb leads to a moderate depression of the canted antiferromagnetic ordering state. The electrical conductivity could be greatly enhanced when the Pb doping content is higher than x=0.2.The present results give a fresh material base to explore new physics in doped Sr_(2)IrO_(4) systems.

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.

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.

A global mantle conductivity model derived from 8 years of Swarm satellite magnetic data

Mantle conductivity imaging is one of the scientific goals of the forthcoming Macao Science Satellite-1(MSS-1).To achieve this goal,we develop a data analysis and inversion scheme for satellite magnetic data to probe global one-dimensional(1D)mantle conductivity structures.Using this scheme,we present a new global mantle conductivity model by analyzing over 8 years of Swarm satellite magnetic data.First,after sophisticated data selection procedures and the removal of core and crustal fields,the inducing and induced spherical harmonic coefficients of magnetic potential due to the magnetospheric ring current are derived.Second,satellite Cresponses are estimated from the time series of these coefficients.Finally,the observed responses are inverted for both smooth and threejump conductivity models using a quasi-Newton algorithm.The obtained conductivity models are in general agreement with previous global mantle conductivity models.A comparison of our conductivity model with the laboratory conductivity model suggests the mean state of the upper mantle and transition zone is relatively dry.This scheme can be used to process the forthcoming Macao Science Satellite-1 magnetic data.

Chaotic Motion Analysis for a Coupled Magnetic-Flow-Mechanical Model of the Rectangular Conductive Thin Plate

The chaotic motion behavior of the rectangular conductive thin plate that is simply supported on four sides by airflow andmechanical external excitation in a magnetic field is studied.According to Kirchhoff’s thin plate theory,considering geometric nonlinearity and using the principle of virtualwork,the nonlinearmotion partial differential equation of the rectangular conductive thin plate is deduced.Using the separate variable method and Galerkin’s method,the system motion partial differential equation is converted into the general equation of the Duffing equation;the Hamilton system is introduced,and the Melnikov function is used to analyze the Hamilton system,and obtain the critical surface for the existence of chaos.The bifurcation diagram,phase portrait,time history response and Poincarémap of the vibration system are obtained by numerical simulation,and the correctness is demonstrated.The results showthatwhen the ratio of external excitation amplitude to damping coefficient is higher than the critical surface,the system will enter chaotic state.The chaotic motion of the rectangular conductive thin plate is affected by different magnetic field distributions and airflow.

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.

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.

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.

Electrochemical, Photophysical, and Magnetic Properties of Green Emitting bis(2,5-Hexyloxy)-Phenylene-<i>alt</i>-Thiophene Fluorescent Conducting Oligomer Addended Fullerene-Diol Dyad

Towards the development of potential new organic photovoltaic and optoelectronic materials, a simple route to synthesize flexibly ether linked fullerene-bis[oligo-(phenylene-alt-thiophene)] and evaluation of electrochemical, photophysical and magnetic properties is presented. Flexible ether linking of oligo-phenylene-thiophene chain to 1, 2 C60(OH)2 is achieved employing Williamson’s ether synthesis. 7-chain phenylene-thiophene chain fluorescent conducting oligomer is synthesized using Grignard coupling reaction with preservation of bromo end groups. Oligomer is highly ordered and soluble in all organic solvents while on linking to fullerene-diol, solubility of adduct restricts only to dimethyl sulfoxide (DMSO). All the synthesized materials are characterized through spectroscopic techniques and molecular weight is determined by mass spectrometry and GPC. Properties of the material indicate the substantial effect of fullerene. High quenching in fluorescence intensity and strong paramagnetic property are observed in this material.

A Double-Phase High-Frequency Traveling Magnetic Field Developed for Contactless Stirring of Low-Conducting Liquid Materials

The use of low electrically conducting liquids is more and more widespread.This is the case for molten glass,salt or slag processing,ionic liquids used in biotechnology,batteries in energy storage and metallurgy.The present paper deals with the design of a new electromagnetic induction device that can heat and stir low electricallyconducting liquids.It consists of a resistance-capacity-inductance circuit coupled with a low-conducting liquid load.The device is supplied by a unique electric power source delivering a single-phase high frequency electric current.The main working principle of the circuit is based on a double oscillating circuit inductor connected to the solid-state transistor generator.This technique,which yields a set of coupled oscillating circuits,consists of coupling a forced phase and an induced phase,neglecting the influence of the electric parameters of the loading part(i.e.,the low-conductivity liquid).It is shown that such an inductor is capable to provide a two-phase AC traveling magnetic field at high frequency.To better understand the working principle,the present work improves a previous existing simplified theory by taking into account a complex electrical equivalent diagram due to the different mutual couplings between the two inductors and the two corresponding induced current sets.A more detailed theoretical model is provided,and the key and sensitive elements are elaborated.Based on this theory,equipment is designed to provide a stirring effect on sodium chloride-salted water at 40 S/m.It is shown that such a device fed by several hundred kiloHertz electric currents is able to mimic a linear motor.A set of optimized operating parameters are proposed to guide the experiment.A pure electromagnetic numerical model is presented.Numerical modelling of the load is performed in order to assess the efficiency of the stirrer with a salt water load.Such a device can generate a significant liquid motion with both controlled flow patterns and adjustable amplitude.Based on the magnetohydrodynamic theory,numerical modeling of the salt water flow generated by the stirrer confirms its feasibility.

A Superconducting Magnet with Center Field of 10 T and φ100 mm Warm Bore

Aconduction-cooled superconducting magnet with central field of 10Tand warmbore of 100 mmwas designed based on a Nb3Sn and two NbTi superconducting coils.At the first stage,the NbTi coils havebeen fabricated andtested.Atwo-stage 4 KGifford-McMahon(GM) cryocooler withthe second-stage powerin1W,4.2Kis used to cool the magnet fromroomtemperature to 4 K.The superconducting magnet with thesame power supply has the operating current of 116A.The magnet can be rotated with a support frame to beoperated with either horizontal or vertical position.Apair of Bi-2223 hightemperature superconductingcurrentleads was employedto reduce heat leakage into 4.2Klevel.The NbTi coils reachto the operating current of120Awithout training effect to be observed duringchargingof the magnet during40 minutes chargingtime andgenerate the center field of 6.5T.The training effect inthe NbTi magnet directly cool-down by cryocooler andinter-winding support structure in magnet can be remarkablyimproved.The superconducting magnet has beenstably operatedfor more than 275 hours with 6.5T.In this paper,the detailed design,fabrication,stressanalysis and quench protection characteristics are presented.

Multi-Functional Nano-Sciences of Advanced Metal Complexes:Photo-Induced Switching between Single-Chain Quantum Magnet and Paramagnet,and Conducting Single-Molecule Quantum Magnets

1 Results In the fields of the molecule-based magnets,the quantum molecular magnets have been attracting much attention. While the bulk magnets or classic magnets are based on the 3D ferro- or ferrimagnetic interaction,the quantum molecular magnets are based on the double-well potential barrier defined with DS2,where D and S are uni-axial anisotropy and spin quantum number,respectively.Therefore,while the memory capacity of the bulk magnets such as floppy disc is 109 bits,the quantum magnets may have th...

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.

MULTI-FIELD COUPLING BEHAVIOR OF SIMPLY-SUPPORTED CONDUCTIVE PLATE UNDER THE CONDITION OF A TRANSVERSE STRONG IMPULSIVE MAGNETIC FIELD

In order to study the multi-field coupling mechanical behavior of the simply-supported conductive rectangular thin plate under the condition of an externally lateral strong impulsive magnetic field, that is the dynamic buckling phenomenon of the thin plates in the effect of the magnetic volume forces produced by the interaction between the eddy current and the magnetic fields, a FEM analysis program is developed to characterize the phenomena of magnetoelastic buckling and instability of the plates. The critical values of magnetic field for the three different initial vibrating modes are obtained, with a detailed discussion made on the effects of the lengththickness ratio a/h of the plate and the length-width ratio a/b as well as the impulse parameter on the critical value BOcr of the applied magnetic field.

Phase, magnetism and thermal conductivity of glass ceramics from iron ore tailings

In order to develop the applications of ore tailings, the glass ceramics were prepared by using a conventional melting-quenching-sintering process. The phase component, microstructures, magnetic properties and thermal conductivities of the prepared glass ceramics were investigated by using X-ray diffractometer, scanning electron microscopy, vibrating sample magnetometer and thermophysical properties tester, respectively. The results show that orthorhombic olivine-type phase and triclinic sunstone-type phase formed when the glass was annealed at 700 oC, the concentration of olivine-type and sunstone-type phases decreased, the spinel-type cubic phase occurred and the amount increased when the annealing temperatures increased. The magnetic properties from the cubic spinel ferrites were detected in the glass ceramics, and the related saturation magnetization increased with the annealing temperature increasing. The porous glass ceramics with magnetic property showed much lower thermal conductivity, compared with the non-magnetic porous glass-ceramic and the dense glass-ceramics.

Thomson and rotation effects during photothermal excitation process in magnetic semiconductor medium using variable thermal conductivity

This study investigates a strong magnetic field acting over an elastic rotator semiconductor medium.The Thomson effect due to the magnetic field during the photothermal transport process is studied,and the thermoelectricity theory is used to explain the behavior of waves in the homogenous and isotropic medium under the effect of variable thermal conductivity.The variable thermal conductivity is considered as a linear function of the temperature.The two-dimensional deformation equations are used to describe the overlaps among plasma,electrical,thermal,and magneto-elastic waves.The charge density of inertia-particles is considered as a function of time for studying the induced electric current.The normal mode analysis is used to obtain the exact solutions of the physical field distributions as part of this phenomenon.To obtain the complete solutions of the physical field quantities,the certain mechanical loads,electromagnetic effects,thermal effects,and plasma recombination process are applied herein.The results of the physical distributions are graphically depicted and discussed in consideration of the internal heat source,rotation,and Peltier coefficient.