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 ferrimagne...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.展开更多
We extend a previous result of ours [G.S. Tian, Phys. Rev. B63 (2001) 224413] on the antiferromagnetic spin correlations in the half-filled Hubbard model at finite temperature to the double-exchange model. To overcome...We extend a previous result of ours [G.S. Tian, Phys. Rev. B63 (2001) 224413] on the antiferromagnetic spin correlations in the half-filled Hubbard model at finite temperature to the double-exchange model. To overcome the mathematical difficulty caused by the localized spin freedom in this model, we apply both Zener's argument and the finite-temperature spin-reflection-positivity method to show rigorously that, at any temperature , the spin correlations in the half-filled double-exchange model are predominantly antiferromagnetic. This conclusion is completely consistent with the experimental observations and the previous theoretical results by approximate methods.展开更多
Magnetic susceptibility of a series of dinuclear Ⅴ(Ⅳ) . Co(Ⅱ) and Mn(Ⅲ) complexes has been measured in the temperature range of 1. 5 ～300K. The isotropic Heisenberg theory has been applied to study the temperatur...Magnetic susceptibility of a series of dinuclear Ⅴ(Ⅳ) . Co(Ⅱ) and Mn(Ⅲ) complexes has been measured in the temperature range of 1. 5 ～300K. The isotropic Heisenberg theory has been applied to study the temperature-dependent behaviour of the magnetic susceptibility of these complexes and a corresponding program for fitting the experimental results has been set up on a VAX 11/785 computer. Conclusions can be drawn that the three complexes studied are all anti-ferromagnetically coupled with coupling constants -4. 4 , -115. 2 , and - 8. 4 cm￣(-1) for Ⅴ(Ⅳ) . Co(Ⅱ) ,and Mn(Ⅲ) complexes, respectively.展开更多
In this work, epitaxial growth of LaMnO3 thin films on different substrates using pulsed laser deposition under tensile and compressive strain was studied. The intrinsic exchange bias effect was observed in the single...In this work, epitaxial growth of LaMnO3 thin films on different substrates using pulsed laser deposition under tensile and compressive strain was studied. The intrinsic exchange bias effect was observed in the single A-type antiferromagnetic LaMnO3 films no matter whether the tensile or compressive strain was supplied by the substrates. Due to the lattice mismatch between the film and different substrates, the intense strain can induce MnO6 octahedral rotation in the bottom region of the film neighboring the substrate, which leads to the distortion of MnO6 octahedron and the net magnetic behavior. However, the upper part maintains the original A-type antiferromagnetic order due to strain relaxation. The exchange bias effect in single films is attributed to the coupling between the bottom canted magnetic part and the upper antiferromagnetic region. The observation of exchange bias in single films on different substrates enables the emergence of a new class of biasing components in spintronics, which are based on strain-engineering.展开更多
The exchange bias is of technological significance in magnetic recording and spintronic devices.Pursuing a large bias field is a long-term goal for the research field of magnetic shape memory alloys.In this work,a lar...The exchange bias is of technological significance in magnetic recording and spintronic devices.Pursuing a large bias field is a long-term goal for the research field of magnetic shape memory alloys.In this work,a large bias field of 0.53 T is achieved in the Ni50Mn34In16-xFex(x=1,3,5)system by tuning the magnetic ground state(determined by the composition x)and the magnetic-field history(determined by the magnetic field HFCduring field cooling and the maximum field HMaxduring isothermal magnetization).The maximum volume fraction of the interfaces between the ferromagnetic clusters and antiferromagnetic matrix and the strong interfacial interaction are achieved by tuning the magnetic ground state and the magnetic-field history,which results in strong magnetic unidirectional anisotropy and the large exchange bias.Moreover,two guidelines were proposed to obtain the large bias field.Firstly,the composition with a magnetic ground state consisting of the dilute spin glass and the strong antiferromagnetic matrix is preferred to obtain a large bias field;secondly,tuning the magnetic-field history by enhancing HFCand reducing HMaxis beneficial to achieving large exchange bias.Our work provides an effective way for designing magnetically inhomogeneous compounds with large exchange bias.展开更多
基金the National Natural Science Foundation of China under
文摘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.
文摘We extend a previous result of ours [G.S. Tian, Phys. Rev. B63 (2001) 224413] on the antiferromagnetic spin correlations in the half-filled Hubbard model at finite temperature to the double-exchange model. To overcome the mathematical difficulty caused by the localized spin freedom in this model, we apply both Zener's argument and the finite-temperature spin-reflection-positivity method to show rigorously that, at any temperature , the spin correlations in the half-filled double-exchange model are predominantly antiferromagnetic. This conclusion is completely consistent with the experimental observations and the previous theoretical results by approximate methods.
文摘Magnetic susceptibility of a series of dinuclear Ⅴ(Ⅳ) . Co(Ⅱ) and Mn(Ⅲ) complexes has been measured in the temperature range of 1. 5 ～300K. The isotropic Heisenberg theory has been applied to study the temperature-dependent behaviour of the magnetic susceptibility of these complexes and a corresponding program for fitting the experimental results has been set up on a VAX 11/785 computer. Conclusions can be drawn that the three complexes studied are all anti-ferromagnetically coupled with coupling constants -4. 4 , -115. 2 , and - 8. 4 cm￣(-1) for Ⅴ(Ⅳ) . Co(Ⅱ) ,and Mn(Ⅲ) complexes, respectively.
基金financially supported by the National Key R&D Program of China (2017YFB0405703)the National Natural Science Foundation of China (51871137, 61434002 and 51571136)the Special Funds of Sanjin Scholars Program
文摘In this work, epitaxial growth of LaMnO3 thin films on different substrates using pulsed laser deposition under tensile and compressive strain was studied. The intrinsic exchange bias effect was observed in the single A-type antiferromagnetic LaMnO3 films no matter whether the tensile or compressive strain was supplied by the substrates. Due to the lattice mismatch between the film and different substrates, the intense strain can induce MnO6 octahedral rotation in the bottom region of the film neighboring the substrate, which leads to the distortion of MnO6 octahedron and the net magnetic behavior. However, the upper part maintains the original A-type antiferromagnetic order due to strain relaxation. The exchange bias effect in single films is attributed to the coupling between the bottom canted magnetic part and the upper antiferromagnetic region. The observation of exchange bias in single films on different substrates enables the emergence of a new class of biasing components in spintronics, which are based on strain-engineering.
基金supported by the National Natural Science Foundation of China(51471127,51431007 and 51371134)the Program for Young Scientific New-star in Shaanxi Province of China(2014KJXX-35)+2 种基金the Innovation Capability Support Program of Shaanxi(2018PT-28 and 2017KTPT-04)Shenzhen Science and Technology Project(JCYJ20180507182246321)the Fundamental Research Funds for Central Universities of China。
文摘The exchange bias is of technological significance in magnetic recording and spintronic devices.Pursuing a large bias field is a long-term goal for the research field of magnetic shape memory alloys.In this work,a large bias field of 0.53 T is achieved in the Ni50Mn34In16-xFex(x=1,3,5)system by tuning the magnetic ground state(determined by the composition x)and the magnetic-field history(determined by the magnetic field HFCduring field cooling and the maximum field HMaxduring isothermal magnetization).The maximum volume fraction of the interfaces between the ferromagnetic clusters and antiferromagnetic matrix and the strong interfacial interaction are achieved by tuning the magnetic ground state and the magnetic-field history,which results in strong magnetic unidirectional anisotropy and the large exchange bias.Moreover,two guidelines were proposed to obtain the large bias field.Firstly,the composition with a magnetic ground state consisting of the dilute spin glass and the strong antiferromagnetic matrix is preferred to obtain a large bias field;secondly,tuning the magnetic-field history by enhancing HFCand reducing HMaxis beneficial to achieving large exchange bias.Our work provides an effective way for designing magnetically inhomogeneous compounds with large exchange bias.
