共查询到20条相似文献,搜索用时 31 毫秒
1.
Kyungwha Park Mark R Pederson Noam Bernstein 《Journal of Physics and Chemistry of Solids》2004,65(4):805-811
A new type of the single-molecule magnet [Mn4O3Cl4(O2CEt)3(py)3] forms dimers. Recent magnetic hysteresis measurements on this single-molecular magnet revealed interesting phenomena: an absence of quantum tunneling at zero magnetic field and tunneling before magnetic field reversal. This is attributed to a significant antiferromagnetic exchange interaction between different monomers. To investigate this system, we calculate the electronic structure, magnetic properties, intramolecular and intermolecular exchange interactions using density-functional theory within the generalized-gradient approximation. Our calculations agree with experiment. We find that the calculated threefold symmetric structure is vibrationally stable. We also calculate vibrational infrared absorption and Raman scattering intensities for the monomer which can be tested experimentally. 相似文献
2.
K. O. Khutsishvili N. P. Fokina 《Journal of Experimental and Theoretical Physics》2009,109(5):794-804
It is shown that antiferromagnetic ordering in doped manganites with strong double-exchange interaction is transformed into
ferromagnetic canted ordering with residual antiferromagnetic behavior in the basal plane as a result of hopping of mobile
electron. The canting angle between the core magnetiztions is controlled by the competition of the Heisenberg antiferromagnetic
exchange and double exchange. The temperatures of the paramagnet-antiferromagnet and paramagnet-canted ferromagnetic phase
transitions are calculated. The results on the dependence of the magnetization in the canted phase and critical temperatures
on the doping degree are in qualitative agreement with experiment. The form of uniform oscillations of core magnetiztions
in the canted ferromagnetic phase of a doped manganite sample with hopping conduction is analyzed with and without allowance
for relaxation of mobile electrons to the lattice. We propose a mechanism for the ferromagnetic resonance broadening and its
resonance frequency shift in a ferromagnetic conducting sample (hopping conduction) of doped manganite due to double exchange.
The resonance frequency shift and the ferromagnetic resonance damping constant (linewidth) are calculated in this model. In
contrast to other relaxation mechanisms, the model is based on the fact that mobile electrons rapidly relax to the lattice
(over a time on the order of the precession period). 相似文献
3.
We investigate multiband Hubbard models for the three iron 3d t(2g) bands and the two iron 3d e(g) bands in LaOFeAs by means of the Gutzwiller variational theory. Our analysis of the paramagnetic ground state shows that neither Hartree-Fock mean-field theories nor effective spin models describe these systems adequately. In contrast to Hartree-Fock-type approaches, the Gutzwiller theory predicts that antiferromagnetic order requires substantial values of the local Hund's-rule exchange interaction. For the three-band model, the antiferromagnetic moment fits experimental data for a broad range of interaction parameters. However, for the more appropriate five-band model, the iron e(g) electrons polarize the t(2g) electrons and they substantially contribute to the ordered moment. 相似文献
4.
Laukhin V Skumryev V Martí X Hrabovsky D Sánchez F García-Cuenca MV Ferrater C Varela M Lüders U Bobo JF Fontcuberta J 《Physical review letters》2006,97(22):227201
The magnetic exchange between epitaxial thin films of the multiferroic (antiferromagnetic and ferroelectric) hexagonal YMnO3 oxide and a soft ferromagnetic (FM) layer is used to couple the magnetic response of the FM layer to the magnetic state of the antiferromagnetic one. We will show that biasing the ferroelectric YMnO3 layer by an electric field allows control of the magnetic exchange bias and subsequently the magnetotransport properties of the FM layer. This finding may contribute to paving the way towards a new generation of electric-field controlled spintronic devices. 相似文献
5.
《Current Applied Physics》2015,15(3):163-168
We have investigated the antiferromagnetic edge states in carbon nanotubes with hydrogen line defects by using the density functional theory calculations. As the hydrogen line defects increase, the exchange energy gain stabilizing the antiferromagnetic edge states increases in each graphenic ribbon produced by the line defects, indicating that the antiferromagnetic edge states can be realized at high temperatures regardless of the nanotube size. The exchange energy gain in each ribbon is determined by the ribbon width of the flat ribbon and apparently by the curvature of the curved ribbon. The exchange interaction between the ribbons is seen to be negligibly small even in the presence of a nonmagnetic inter-ribbon interaction that is sensitive to the ribbon width. 相似文献
6.
Bagno A Rastrelli F Scorrano G 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2004,167(1):31-35
We present a pulse sequence based on solute-to-solvent NOE enhancement and aimed at the detection of intermolecular NOE's. Thus, a W3 pulse cluster is used to selectively filter the solvent signals in a DPFGSE sequence. The sequence has been tested on a sample of glucose dissolved in two binary aqueous mixtures (water-acetonitrile and water-DMSO). We show how the resulting enhancements may derive from intermolecular cross-relaxation or, in the water-DMSO sample, also from chemical exchange. In each case, a quantitative interpretation of the data is also supplied, both in terms of local enrichment in one specific solvent (preferential solvation), and by means of a kinetic model for a two-site chemical exchange. 相似文献
7.
La$lt;sub$gt;0.4$lt;/sub$gt;Ca$lt;sub$gt;0.6$lt;/sub$gt;MnO$lt;sub$gt;3$lt;/sub$gt;中Mn-位Fe和Cr掺杂对磁性质的影响
下载免费PDF全文
![点击此处可从《物理学报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
研究了Fe和Cr掺杂对La0.4Ca0.6MnO3 中电荷有序反铁磁基态的调控作用. 磁性质的测量结果表明, 两种离子掺杂均能有效抑制原型样品中的长程电荷有序相, 但是Fe离子掺杂样品均具有反铁磁的基态, 而Cr掺杂样品中则出现了显著的铁磁性. 结合电输运测量结果显示, Cr掺杂引起的铁磁态同时具有金属性, 表明其中是电子双交换作用占主导. 对比两种掺杂离子的电子结构发现, Cr离子空的eg电子轨道促进了电子双交换作用, 而Fe掺杂则只是引入了不同的自旋交换作用, 导致自旋无序.
关键词:
磁性氧化物
反铁磁 相似文献
8.
We study the full counting statistics (FCS) in a single-molecule magnet (SMM) with finite Coulomb interaction U. For finite U the FCS, differing from U→∞, shows a symmetric gate-voltage-dependence when the coupling strengths with two electrodes are interchanged, which can be observed experimentally just by reversing the bias-voltage. Moreover, we find that the effect of finite U on shot noise depends on the internal level structure of the SMM and the coupling asymmetry of the SMM with two electrodes as well. When the coupling of the SMM with the incident-electrode is stronger than that with the outgoing-electrode, the super-Poissonian shot noise in the sequential tunneling regime appears under relatively small gate-voltage and relatively large finite U, and dose not for U→∞; while it occurs at relatively large gate-voltage for the opposite coupling case. The formation mechanism of super-Poissonian shot noise can be qualitatively attributed to the competition between fast and slow transport channels. 相似文献
9.
We study theoretically the spin dynamics of a magnetic dimer serving as a contact between two electrodes. We find that the spin-spin coupling in the dimer can be dramatically modified from its equilibrium value. We show that the interaction can be tuned in such a way that it effectively changes its sign. The calculations show that, for large enough bias, the exchange interaction can even be changed from antiferromagnetic to ferromagnetic. The physical principles behind this result can be used as a new tool to achieve magneto-electric effects in molecular magnet systems. 相似文献
10.
Entanglement and quantum phase transition in alternating XY spin chain with next-nearest neighbouring interactions
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
By using the method of density-matrix renormalization-group to solve the different spin spin correlation functions, the nearest-neighbouring entanglement (NNE) and the next-nearest-neighbouring entanglement (NNNE) of one-dimensional alternating Heisenberg XY spin chain are investigated in the presence of alternating the-nearestneighbouring interaction of exchange couplings, external magnetic fields and the next-nearest neighbouring interaction. For a dimerised ferromagnetic spin chain, the NNNE appears only above a critical dimerized interaction, meanwhile, the dimerized interaction a effects a quantum phase transition point and improves the NNNE to a large extent. We also study the effect of ferromagnetic or antiferromagnetic next-nearest neighbouring (NNN) interaction on the dynamics of NNE and NNNE. The ferromagnetic NNN interaction increases and shrinks the NNE below and above a critical frustrated interaction respectively, while the antiferromagnetic NNN interaction always reduces the NNE. The antiferromagnetic NNN interaction results in a large value of NNNE compared with the case where the NNN interaction is ferromagnetic. 相似文献
11.
Zhao HB Talbayev D Ma X Ren YH Venimadhav A Li Q Lüpke G 《Physical review letters》2011,107(20):207205
Pronounced spin precessions are observed in a geometry with negligible canting of the magnetization in ferromagnetic La(0.67)Ca(0.33)MnO(3) thin films using the time-resolved magneto-optical Kerr effect. The precession amplitude monotonically decreases with increasing field, indicating that the coherent spin rotation may be triggered by a transient exchange field and not by demagnetization and/or anisotropy field modulation. We attribute the transient exchange field to emergent antiferromagnetic interactions due to charge transfer and modification of the kinetic energy of e(g) electrons under optical excitation. 相似文献
12.
在带有垂直各向异性的二维三角晶格磁体中,当同时存在最近邻铁磁性和第三近邻反铁磁性交换作用时,垂直于膜面施加外磁场会使体系内自旋沿着非共面的方向排列,甚至出现拓扑稳定的斯格明子自旋结构.基于蒙特卡罗模拟方法,本文研究了在该二维阻挫磁体中,竞争性交换作用和外磁场对斯格明子直径的影响.与常规非中心对称的手性磁体中的斯格明子性质类似,外磁场会磁化斯格明子外围自旋而减小斯格明子直径.但是,磁体中反铁磁性交换作用的增强会整体压缩斯格明子.本文结合自旋波理论和蒙特卡罗模拟,首次量化了此类阻挫磁体中斯格明子的直径.结果表明:在弱的反铁磁性交换作用磁体中,斯格明子直径随磁场增大而快速线性减小;随着反铁磁性交换作用的增大,斯格明子直径随外磁场增大的减小变得相对平缓,但在强磁场下也会造成斯格明子直径的加速减小;随着反铁磁性交换作用的增强,斯格明子在不同外磁场下的直径的最大值和中值均从逐渐减小到渐趋稳定,而直径的最小值则从快速减小到表现出很大的涨落.这些现象都可以通过分析斯格明子在不同交换作用和外磁场下的构型和磁能变化加以解释.该项工作阐明了在中心对称的阻挫磁体中斯格明子直径的可调节性,不仅完善了我们对斯格明子本身物理机理的认识,同时也为发展基于斯格明子的新一代存储和逻辑器件提供了理论支撑. 相似文献
13.
We present evidence for the creation of an exchange spring in an antiferromagnet due to exchange coupling to a ferromagnet. X-ray magnetic linear dichroism spectroscopy on single crystal Co/NiO(001) shows that a partial domain wall is wound up at the surface of the antiferromagnet when the adjacent ferromagnet is rotated by a magnetic field. We determine the interface exchange stiffness and the antiferromagnetic domain wall energy from the field dependence of the direction of the antiferromagnetic axis, the antiferromagnetic pendant to a ferromagnetic hysteresis loop. The existence of a planar antiferromagnetic domain wall, proven by our measurement, is a key assumption of most exchange bias models. 相似文献
14.
We report high-resolution observations of antiferromagnetic (AF) domain walls at the surface of NiO and determine the typical width of AF walls in this material to be of the order of 150 nm. We observe a number of different types of domain walls, including double walls caused by long-range interaction between walls. We describe the observed wall profiles by a model containing the exchange interaction and magnetostriction as basic ingredients. The good agreement of this model with experiment shows that the formation of walls between antiferromagnetic domains in NiO and their properties are dominated by magnetoelastic interactions. 相似文献
15.
Alexandra Imre Gyrgy Csaba Gary H. Bernstein Wolfgang Porod Vitali Metlushko 《Superlattices and Microstructures》2003,34(3-6):513
This paper presents a magnetic force microscopy study of antiferromagnetic ordering along chains of dipole-coupled single-domain permalloy nanomagnets with a variety of shapes. Magnetization reversal processes occur due to antiferromagnetic coupling between the closely spaced dots when an appropriate external magnetic field is applied. The goal of this study was to investigate the switching properties and correlation lengths as a function of nanomagnet geometry. We have found that certain shapes (due to their stronger stray fields) clearly show stronger interaction than others when the chain is demagnetized. In addition we have seen that the performance of the nanomagnets also depends on the method of demagnetization, and this fact must be taken into account when shape engineering is used to design coupled nanomagnet systems for a given application. 相似文献
16.
T. V. Drokina G. A. Petrakovskii O. A. Bayukov A. M. Vorotynov D. A. Velikanov M. S. Molokeev 《Physics of the Solid State》2016,58(10):1981-1988
Complex studies have been performed for the structural, static magnetic, and resonance properties of a new magnet LiCuFe2(VO4)3 prepared by solid-phase synthesis. The temperature dependence of the susceptibility has an anomaly at temperature Tmax = 9.6 K. At high temperatures, the LiCuFe2(VO4)3 sample is in the paramagnetic state described by the Curie–Weiss law at T > 50 K and mainly determined by iron ions with effective magnetic moment μeff(exp) = 8.6μB per formula unit. At low temperatures, a long-range magnetic order is observed in the magnetic subsystem of the sample; the order is predominantly characterized by the antiferromagnetic exchange interaction and high frustration level. The exchange interaction parameters are estimated in a six-sublattice representation of the LiCuFe2(VO4)3 magnet. It is shown that the LiCuFe2(VO4)3 compound is an antiferromagnet with strong intrachain and frustrating interchain exchange interactions. 相似文献
17.
YAOJian-Guo PENGGuang-Xiong 《理论物理通讯》2004,42(5):798-800
The electronic structure and the magnetic properties of the non-pure organic ferromagnetic compound MnCu(pbaOH)(H2O)3 with pbaOH=2-hydroxy-1, 3-propylenebis (oxamato) are studied by using the density-functional theory with local-spin-density approximation. The density of states, total energy, and the spin magnetic moment are calculated. The calculations reveal that the compound MnCu(pbaOH)(H2O)3 has a stable metal-ferromagnetic ground state, and the spin magnetic moment per molecule is 2.208 μa, and the spin magnetic moment is mainly from Mn ionand Cu ion. An antiferromagnetic order is expected and the antiferromagnetic exchange interaction of d-electrons of Cu and Mn passes through the antiferromagnetic interaction between the adjacent O, 0, and N atoms along the path linking the atoms Cu and Mn. 相似文献
18.
Norgaard K Eskildsen MR Andersen NH Jensen J Hedegard P Klausen SN Canfield PC 《Physical review letters》2000,84(21):4982-4985
We have discovered a new antiferromagnetic phase in TmNi2B2C by neutron diffraction. The ordering vector is Q(A) = (0.48,0,0) and the phase appears above a critical in-plane magnetic field of 0.9 T. The field was applied in order to test the assumption that the zero-field magnetic structure at Q(F) = (0.094,0.094,0) would change into a c-axis ferromagnet if superconductivity were destroyed. We present theoretical calculations which show that two effects are important: a suppression of the ferromagnetic component of the RKKY exchange interaction in the superconducting phase and a reduction of the superconducting condensation energy due to the periodic modulation of the moments at Q(A). 相似文献
19.
Sánchez-Marcos J Angeles Laguna-Marco M Martínez-Morillas R Céspedes E Jiménez-Villacorta F Menéndez N Prieto C 《J Phys Condens Matter》2011,23(47):476003
Iron oxide nanoclusters have been prepared by the gas-phase aggregation technique to form thin film structures with very high exchange bias values (up to 3000?Oe at low temperatures). Composition has been analysed by x-ray absorption and M?ssbauer spectroscopies in order to elucidate the actual origin of the observed magnetic behaviour. The formation of a metal-oxide core-shell arrangement to explain the observed exchange bias has to be discarded since results show no metallic iron content and the main presence of α-Fe(2)O(3). The observed weak ferromagnetism and exchange bias are in agreement with the obtained size of α-Fe(2)O(3) nanoparticles: weak ferromagnetism because of the well-known spin canting in this antiferromagnetic structure and exchange bias because of the interaction between different spin sublattice configurations promoted by the modification of iron coordination in α-Fe(2)O(3) nanoparticles. Moreover, the preparation method is proposed for tuning both magnetization and exchange bias values by modification of the preparation conditions of α-Fe(2)O(3) nanoparticles, which open new possibilities in the design of new materials with required properties. 相似文献
20.
We investigate the scanning tunneling spectroscopy (STS) of a two-orbital Anderson impurity
adsorbed on a metallic surface by using the numerical renormalization group (NRG) method. The density
of state of magnetic impurity and the local conduction electron are calculated. We obtain the Fano
resonance line shape in the STM conductance at zero temperature. For the impurity atom with
antiferromagnetic inter-orbital exchange interaction and a spin singlet ground state, we show that a
dip in the STM spectra around zero bias voltage regime and side peaks of spin excitation can be
observed. The spin excitation energy is proportional to the exchange interaction strength. As the
exchange interaction is ferromagnetic, the underscreened Kondo effect dominates the low energy
properties of this system, and it gives rise to drastically different STM spectra as compared with the
spin singlet case. 相似文献