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41.
A new manganese-based single-molecule magnet with a record-high antiferromagnetic phase transition temperature 下载免费PDF全文
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. 相似文献
42.
We generalize the Heisenberg star consisting of a spin-1/2 central spin and a homogeneously coupled spin bath modeled by the XXX ring [Richter J and Voigt A 1994 J. Phys. A: Math. Gen. 27 1139-1149] to the case of arbitrary central-spin size S < N/2, where N is the number of bath spins. We describe how to block-diagonalize the model based on the Bethe ansatz solution of the XXX ring, with the dimension of each block Hamiltonian ≤ 2S + 1. We obtain all the eigenenergies and explicit expressions of the sub-ground states in each l-subspace with l being the total angular momentum of the bath. Both the eigenenergies and the sub-ground states have distinct structures depending whether S ≤ l or l < S. The absolute ground-state energy and the corresponding l as functions of the intrabath coupling are numerically calculated for N = 16 and S = 1, 2, ⋯ ,7 and their behaviors are quantitatively explained in the weak and strong intrabath coupling limits. We then study the dynamics of the antiferromagnetic order within an XXX bath prepared in the Néel state. Effects of the initial state of the central spin, the value of S, and the system-bath coupling strength on the staggered magnetization dynamics are investigated. By including a Zeeman term for the central spin and the anisotropy in the intrabath coupling, we also study the polarization dynamics of the central spin for a bath prepared in the spin coherent state. Under the resonant condition and at the isotropic point of the bath, the polarization dynamics for S > 1/2 exhibit collapse-revival behaviors with fine structures. However, the collapse-revival phenomena are found to be fragile with respect to the anisotropy of the intrabath coupling. 相似文献
43.
Magnetic polaron-related optical properties in Ni(Ⅱ)-doped Cd S nanobelts: Implication for spin nanophotonic devices 下载免费PDF全文
Emissions by magnetic polarons and spin-coupled d-d transitions in diluted magnetic semiconductors(DMSs)have become a popular research field due to their unusual optical behaviors.In this work,high-quality NiI2(Ⅱ)-doped CdS nanobelts are synthesized via chemical vapor deposition(CVD),and then characterized by scanning electron microscopy(SEM),x-ray diffraction,x-ray photoelectron spectroscopy(XPS),and Raman scattering.At low temperatures,the photoluminescence(PL)spectra of the Ni-doped nanobelts demonstrate three peaks near the band edge:the free exciton(FX)peak,the exciton magnetic polaron(EMP)peak out of ferromagnetically coupled spins coupled with FXs,and a small higher-energy peak from the interaction of antiferromagnetic coupled Ni pairs and FXs,called antiferromagnetic magnetic polarons(AMPs).With a higher Ni doping concentration,in addition to the d-d transitions of single Ni ions at 620 nm and 760 nm,two other PL peaks appear at 530 nm and 685 nm,attributed to another EMP emission and the d-d transitions of the antiferromagnetic coupled Ni2+-Ni2+pair,respectively.Furthermore,single-mode lasing at the first EMP is excited by a femtosecond laser pulse,proving a coherent bosonic lasing of the EMP condensate out of complicated states.These results show that the coupled spins play an important role in forming magnetic polaron and implementing related optical responses. 相似文献
44.
Xiao-Fang Ouyang 《中国物理 B》2022,31(7):77304-077304
Exploring the half-metallic nanostructures with large band gap and high carrier mobility is a crucial solution for developing high-performance spintronic devices. The electric and magnetic properties of monolayer zigzag black-phosphorene nanoribbons (ZBPNRs) with various widths are analyzed by means of the first-principles calculations. Our results show that the magnetic ground state is dependent on the width of the nanoribbons. The ground state of narrow nanoribbons smaller than 8ZBPNRs prefers ferromagnetic order in the same edge but antiferromagnetic order between two opposite edges. In addition, we also calculate the electronic band dispersion, density of states and charge density difference of 8ZBPNRs under the action of out-of-plane electric field. More interesting, the addition of out-of-plane field can modulate antiferromagnetic semiconductor to the half metal by splitting the antiferromagnetic degeneracy. Our results propose a new approach to realize half-metal in phosphorene, which overcomes the drawbacks of graphene/silicene with negligible band gap as well as the transitional metal sulfide (TMS) with low carrier mobility. 相似文献
45.
Large inverse and normal magnetocaloric effects in HoBi compound with nonhysteretic first-order phase transition 下载免费PDF全文
HoBi single crystal and polycrystalline compounds with NaCl-type structure are successfully obtained, and their magnetic and magnetocaloric properties are studied in detail. With temperature increasing, HoBi compound undergoes two magnetic transitions at 3.7 K and 6 K, respectively. The transition temperature at 6 K is recognized as an antiferromagnetic-to-paramagnetic (AFM-PM) transition, which belongs to the first-order magnetic phase transition (FOMT). It is interesting that the HoBi compound with FOMT exhibits good thermal and magnetic reversibility. Furthermore, a large inverse and normal magnetocaloric effect (MCE) is found in HoBi single crystal in the $H|| [100]$ direction, and the positive $\Delta S_{\rm M}$ peak reaches 13.1 J/kg$\cdot$K under a low field change of 2 T and the negative $\Delta S_{\rm M}$ peak arrives at $-18 $ J/kg$\cdot$K under a field change of 5 T. These excellent properties are expected to be applied to some magnetic refrigerators with special designs and functions. 相似文献
46.
47.
Solitons and intrinsic localized modes in a one-dimensional antiferromagnetic chain 总被引:3,自引:0,他引:3 下载免费PDF全文
By use of the Hartree approximation and the method of multiple scales, we
investigate quantum solitons and intrinsic localized modes in a
one-dimensional antiferromagnetic chain. It is shown that there exist
solitons of two different quantum frequency bands: i.e., magnetic optical
solitons and acoustic solitons. At the boundary of the Brillouin zone, these
solitons become quantum intrinsic localized modes: their quantum
eigenfrequencies are below the bottom of the harmonic optical frequency band
and above the top of the harmonic acoustic frequency band. 相似文献
48.
YAO Kai-Lun QIN Yi LIU Qing-Mei LIU Zu-Li 《理论物理通讯》2005,44(6):1099-1102
By using density matrix renormalization group (DMRG) method a model for organic molecule-based ferromagnetic chain is proposed. It is found that the ground states of Undoped and doped systems both exhibit ferrimagnetic ordering. The e-e repulsion plays an important role in the stability of the ferromagnetic state either in doped system or undoped system. For the undoped system, each unit cell coatains half of the total spins, which is consistent with Lieb's theorem. It is convinced that when the system is doped with one electron, a charge density wave is excited, which decreases the amplitude of spin density wave,therefore acting against the stability of ferromagnetic state. 相似文献
49.
The temperature dependence of exchange bias and coercivity in a
ferromagnetic layer coupled with an antiferromagnetic layer is discussed. In
this model, the temperature dependence comes from the thermal instability of
the system states and the temperature modulated relative magnetic
parameters. Morever, the thermal fluctuation of orientations of easy axes of antiferromagnetic grains at preparing has been considered. From the present model, the experimental results can be illustrated qualitatively for
available magnetic parameters. Based on our discussion, we can conclude that
soft ferromagnetic layer coupled by hard antiferromagnetic layer may be very
applicable to design magnetic devices. In special exchange coupling, we can
get high exchange bias and low coercivity almost independent of temperature for proper temperature ranges. 相似文献
50.