Dynamic Stiffness Analysis and Experimental Verification of Axial Magnetic Bearing Based on Air Gap Flux Variation in Magnetically Suspended Molecular Pump

Current and displacement stiffness are important parameters of axial magnetic bearing(AMB)and are usually considered as constants for the control system.However,in actual dynamic work situations,time-varying force leads to time-varying currents and air gap with a specific frequency,which makes the stiffness of appear decrease and even worsens control performance for the whole system.In this paper,an AMB dynamic stiffness model considering the flux variation across the air gap due to frequency is established to obtain the accurate dynamic stiffness.The dynamic stiffness characteristics are analyzed by means of the dynamic equivalent magnetic circuit method.The analytical results show that the amplitude of current and displacement stiffness decreases with frequency increasing.Moreover,compared with the stiffness model without considering the variation of flux density across the air gap,the improved dynamic stiffness results are closer to the actual results.Through the dynamic stiffness measurement method of AMB,experiments of AMB in magnetically suspended molecular pump(MSMP)are carried out and the experimental results are consistent with theoretical analysis results.This paper proposes the dynamic stiffness model of axial magnetic bearing considering the variation of flux density across the air gap,which improves the accuracy of the AMB stiffness analysis.

Gate-Voltage-Induced Magnetization Reversal and Tunneling Anisotropic Magnetoresistance in a Single Molecular Magnet with Temperature Gradient

We study the coutrol of gate voltage over the magnetization of a single-molecule magnet （SMM） weakly coupled to a ferromagnetic and a normal metal electrode in the presence of the temperature gradient between two electrodes. It is demonstrated that the SMM＇s magnetization can change periodically with periodic gate voltage due to the driving oI the temperature gradient. Under an appropriate matching of the electrode polarization, the temperature difference and the pulse width of gate voltage, the SMM＇s magnetization can be completely reversed in a period of gate voltage. The corresponding flipping time can be controlled by the system parameters. In addition, we also investigate the tunneling anisotropic magnetoresistance （TAMFt） of the device in the steady state when the ferromagnetic electrode is noncollinear with the easy axis of the SMM, and show the jump characteristic of the TAMR.

Controllable Optical Bistability in a Crystal of Molecular Magnets System

We investigate the formation of optical bistability （OB） in a crystal of molecular magnets contained in a unidirectional ring cavity. The crystal is subjected to one dc magnetic field and two （probe and coupling） ac resonant magnetic field. The results show that OB can be controlled efficiently by adjusting the intensity of the control field, the detuning of probe magnetic field and the cooperation parameter, Furthermore, within certain parameter range, the optical multistablity （OM） can also be observed in the crystal medimn. This＇ investigation can be used for designing new types of nonelectronic devices for realizing switching process.

Macroscopic Quantum Coherence in Antiferromagnetic Molecular Magnets

The macroscopic quantum coherence in a biaxial antiferromagnetic molecular magnet in the presence of magnetic field acting parallel to its hard anisotropy axis is studied within the two-sublattice model. On the basis of instanton technique in the spin-coherent-state path-integral representation, both the rigorous Wentzel-Kramers-Brillouin exponent and pre-exponential factor for the ground-state tunnel splitting are obtained. We find that the quantum fluctuations around the classical paths can not only induce a new quantum phase previously reported by Chiolero and Loss (Phys. Rev. Lett. 80 (1998) 169), but also have great influence on the intensity of the ground-state tunnel splitting. Those features clearly have no analogue in the ferromagnetic molecular magnets. We suggest that they may be the universal behaviors in all antiferromagnetic molecular magnets. The analytical results are complemented by exact diagonalization calculation.

Effects of Arbitrarily Directed Field on Spin Phase Oscillations in Biaxial Molecular Magnets

Quantum phase interference and spin-parity effects are studied in biaxial molecular magnets in a magnetic field at an arbitrarily directed angle. The calculations of the ground-state tunnel splitting are performed on the basis of the instanton technique in the spin-coherent-state path-integral representation, and complemented by exactly numerical diagonalization. Both the Wentzel–Kramers–Brillouin exponent and the pre-exponential factor are obtained for the entire region of the direction of the field. Our results show that the tunnel splitting oscillates with the field for the small field angle, while for the large field angle the oscillation is completely suppressed. This distinct angular dependence, together with the dependence of the tunnel splitting on the field strength, provides an independent test for spin-parity effects in biaxial molecular magnets. The analytical results for the molecular magnet are found to be in good agreement with the numerical simulations, which suggests that even the molecular magnet with total spin is large enough to be treated as a giant spin system.

Phonon-Assisted Spin Current in Single Molecular Magnet Junctions

Owing to the bistable character of the single molecular magnet （SMM）, it can generate 100% spin-polarized currents even connected with normal （N） leads. In this work, we study the phonon-assisted spin current in N- SMM-N systems. We mainly focus on the interplay of SMM＇s bistable character and electron-phonon coupling. It is found that when SMM is trapped in one of the lowest bistable states, it can generate phonon-assisted spin- polarized currents. At the up-spin transport channel, it is accompanied by a phonon-assisted up-spin current, while at the down-spin transport channel, it is accompanied by a phonon-assisted down-spin current.

First Principle Study on the Magnetic and Electric Properties of Wurtzite Cr-phosphides and Cr-sulphides： Several Half-metallic Ferromagnets

The geometrical structures of wurtzite CrX （X=As, Sb, O, Se, and Te） were optimized, then their electric and magnetic properties were investigated by the first-principle calculations within the generalized gradient approximation for the exchange-correlation functional based on the density functional theory. These Cr-phosphides and Cr-sulphides were predicted to be half-metallic ferromagnets whose spin-polarization at the Fermi level is absolutely 100%. The molecular magnetic moments of Cr-phosphides and Cr-sulphides are 3.00 and 4.00 μB, which arise mainly from Cr-ions, respectively. There is ferromagnetic coupling in both Cr- phosphides and Cr-sulphides. The Curie temperatures of Cr-sulphides and Cr-phosphides are high. The electronic structures of Cr-ions are a1g^2↑↓t1u^4↑↓t1u^1↑↓eg^2↑↓in Cr-phosphides and a1g^2↑↓t1u^4↑↓t1u^1↑t2g^3↑in Cr-sulphides, respectively.

Crystal Structure and Magnetic Properties of the Oxamidato-bridged Cu_3 Complex Containing Macrocyclic Ligands

One novel oxamido-bridged trinuclear complex [Cu（CuL）2（ClO4）2] has been syn-thesized and structurally determined.It crystallizes in the monoclinic system,space group P21/n with a = 10.636（4）,b = 11.645（4）,c = 16.038（6） ,β = 91.029（5）°,V = 1986.2（12） 3,C38H32Cl2Cu3N8O12,Mr = 1054.24,Dc = 1.763 Mg/m3,μ（MoKα） = 1.802 mm-1,F（000） = 1066,Z = 2,the final R = 0.0328 and wR = 0.0882 for 3152 observed reflections.The crystal structure is a trinuclear complex in which the CuII ions are bridged by macrocyclic oxamide groups.C-H···O hydrogen bonding interactions link the trinuclear fragment to form a 2D supramolecular architecture.Magnetic measurements indicate that the compound is moderately antiferromagnetically coupled.

Shot noise of the spin inelastic tunneling through a quantum dot with single molecule-magnet

We have studied the quantum fluctuations of inelastic spin-electron scattering in quantum dot with an embedded biaxial single molecule-magnet and particularly investigated the zero-frequency shot noise and Fano factor in different magnetic fields. It is found that the shot noise and Fano factor exhibit a stepwise behaviour as bias increases in the presence of interaction between the electron and molecule-magnet for a weak magnetic field. As magnetic field becomes strong, a dip is displayed in the shot-noise-bias curve due to the suppression of inelastic shot noise caused by the quantum tunneling of magnetisation. Because of the spontaneous inelastic tunneling at zero bias, a small shot noise occurs, which results in the case of Fano factor F ≥ 1. Moreover, our results show that the sweeping speed can also influence the shot noise and Fano factor obviously.

Magnetoelastic instability in the XXZ rings with next-nearest neighbour coupling

This paper numerically investigates the magnetoelastic instability in the S = 1/2 {XXZ} rings containing finite spins N with antiferromagnetic nearest-neighbour （{NN}） and next-nearest neighbour （{NNN}） coupling. It finds that, as the {NN} anisotropy Δ1 equals the {NNN} anisotropy ／varDelta2, there exists a critical {NNN} coupling strength J2c（≈0.5）, at which the systems always locate in dimerized phase for arbitrary large spring constant. As Δ1 ／ne Δ2, the values of J2^{／rm c} are dependent on N and the difference of （Δ1-／varDelta2）.

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.

Multi-step shot noise spectrum induced by a local large spin

We use non-equilibrium Green＇s function method to analyze the shot noise spectrum of artificial single molecular magnets（ASMM） model in the strong spin–orbit coupling limit in sequential tunneling regime, mainly focusing on the effects of local large spin. In the linear response regime, the shot noise shows 2S ＋ 1 peaks and is strongly spin-dependent.In the nonlinear response regime, one can observe 2S ＋ 1 steps in shot noise and Fano factor. In these steps one can see the significant enhancement effect due to the spin-dependent multi-channel process of local large spin, which reduces electron correlations.

Synthesis,Structural Characterization and Magnetic Properties of{[Gd(DMF)_(3)(DMSO)(H_(2)O)_(3)](μ-CN)(Fe)(CN)_(5)]}·2H_(2)O

A new cyano-bridged Gadolinium^(Ⅲ)-Iron^(Ⅲ)complex{[Gd(DMF)_(3)(DMSO)(H_(2)O)_(3)]2H_(2)0(DMF=N,N·-dimethylformamide;DMSO=dimethylsulfoxidel}was synthesized by the grinding reaction method,.It crysta-]llizes in the triclinic.,space group P1 with ceIl parameters:a=O.90363(2)nm,b=1.25078(3)nm,c=1.41303(1)nm,穋m^(-3),Z=2,Mr=756.72,F(000)=760,Ⅲ)and the approxi-mately oriented octahedrally sixfold-coordinated Fe(Ⅲ)are linked by a cyano-bridge group to construct a dinuclear compound.The{[Gd(DMF)_(3)(DMSO)(H_(2)O)_(3)](Ⅲ)-Fe(Ⅲ)interaction is antiferromagnetic.CCDC:223430.

Molar ratio induced crystal transformation from coordination complex to coordination polymers

Coordination complex of a copper cyanurate(Cu(Ⅱ)-CA) was transformed into coordination polymers upon the stimulus of extra Cu(Ⅱ) through “directed Ostwald ripening”. By increasing the molar ratio of Cu(Ⅱ) to CA, we obtained two coordination polymers with selective coordination sites: Cu(Ⅱ)-κ N(HCA)κ NCu(Ⅱ) and Cu(Ⅱ)-κ N(HCA)κ O-Cu(Ⅱ), which display disparate magnetic interactions.

An introduction to molecular spintronics

We review the progress and future possibilities in the emerging area of molecular spintronics. We first provide an overview of the different transport regimes in which electronic nanodevices can operate, then briefly overview the important characteristics of molecular magnetic materials that can be useful for application in spintronics and we eventually present several schemes to include such systems into spintronic nanodevices. We hightlight the importance of a chemical approach to the area, and in the last section we showcase some approaches to the creation of hybrids made of carbon nanostructures and molecular magnets, which are gaining increasing attention.

Molecular-based conducting magnet

Molecular-based conducting magnet or magnetic conductor, is an overlap of organic conductor and molecular magnet. Due to the existence of ferromagnetism, antiferromagnetism and quantum magnetism in insulated charge-transfer salt, it becomes a common sense that magnetism is not good for conductivity. After the discovery of first molecular-based metallic ferromagnet, molecular-based conducting magnet with n-unit from organic conductor and magnetism from coordination counterion became a hot area. The metallic ferromagnet, semiconductor room-temperature ferrimagnet, metallic weak ferromagnet and supercon- ducting antiferromagnet have been discovered. The new molecular-based conducting magnet with higher conductivity and higher magnetic ordering temperature is expected.

Synthesis,Structure,and Optical-response Magnetic Property of a Heteroarene-azo Functionalized Mn_(19) Cluster

Metal clusters with photoswitching ligands can undergo magnetic changes under light radiation,which makes them potential optical-response magnetic-switching materials.Herein,a photoswitchable Mn-oxo cluster[Mn^(II)_(15)Mn^(III)_(4)(L)_(18)(OH)_(12)(N_(3))_(6)](ClO_(4))_(2)(C_(6)H_(5)CN)_(8),(Mn19azo,HL=1-(hydroxymethyl)-3,5-dimethyl-4-(phenyldiazenyl)-pyrazole)has been designed and synthesized to realize the photoswitching behavior.Mn19azo shows quick trans-to-cis transformation upon 365 nm light irradiation in CH2Cl2 solution and solid state as confirmed by UV-Vis spectra.After the powder sample was irradiated for 80 min,the Curie constant of Mn19azo increases by about 7%.The change of magnetic properties can be considered as the result of the change of intermolecular interactions.

Magnetic and electro-catalytic properties of a copper complex with 2-(pyridylmethyl)amino-N,N-bis(2-methylene-4,6-difluorophenol)

A new material for both magnetic coupling and electrocatalytic hydrogen generation based on a copper complex,[（HL）CuCl-CuCl（HL）]HCl 1 is prepared by the reaction of 2-（pyridylmethyl）amino-N,N-bis（2-methylene-4,6-difluorophenol）（H2L） and CuCl2·2H2O.In solid,complex 1 is built from two copper units（[（HL）CuCl]）,and exhibits an antiferromagnetic exchange interaction between copper（Ⅱ） ions（J=-160cm^-1）.In liquid,1 can electrocatalyze hydrogen generation both from acetic acid with a turnover frequency（TOF） of 16.3 moles of hydrogen per mole of catalyst per hour at an overpotential（OP）of 941.6 mV（in DMF）,and a neutral buffer with a TOF of 1415.6 moles of hydrogen per mole of catalyst per hour at an OP of 787.6 mV.

Shape and magnetic moment dependence of the dipolar field in Mn_(12)-acetate

There is a small fraction of fast-relaxation species in Mn12-acetate, which is utilized to determine the dipolar field of Mn12. Here we report an easier way to precisely obtain the dipolar field by measuring the M-H curves above the blocking temperature of fastrelaxation species. We found that there is a simple linear relationship between the magnetic moment and dipolar field; besides the dipolar field is also dependent on the sample shape, which is consistent with the numerical calculation.

Cyanido-bridged one-dimensional systems assembled from [Re~ⅣCl_4(CN)_2]_(2-) and [M~Ⅱ(cyclam)]^(2+) (M=Ni,Cu) precursors

Three new cyanido-bridged heterometallic ReIVNin and ReIVCu one-dimensional systems were synthesized and extensively characterized both structurally and magnetically. Single-crystal X-ray diffraction analysis revealed that these compounds display a common topology, with chains composed of alternating [RetVc14（CN）2]2- and [Mn（cyclam）]2＋ （M = Ni in 1, Cu in 2） or [Cull（N,N＇-dimethylcyclam）]2＋ （in 3） building units. Two different chain orientations with a tilt angle of ca. 51° to 55° are present in the crystal packing of these compounds. The magnetic susceptibility measurements suggest the presence of intrachain ferromagnetic interactions between the S = 3/2 ReTM centers and the 3d metal ions： S = 1 Ni1I or S = 1/2 CuII. At low temperature, a three-dimensional ordered magnetic phase induced by interchain antiferromagnetic interactions （antiferromagnetic for 1 and 2; canted antiferromagnetic for 3） is detected for the three compounds.