共查询到20条相似文献,搜索用时 31 毫秒
1.
Pertti Hakonen Olli V. Lounasmaa Aarne Oja 《Journal of magnetism and magnetic materials》1991,100(1-3):394-412
Owing to the weak mutual interactions, spontaneous nuclear magnetic ordering in metallic copper and silver occurs at 60 nK and 560 pK, respectively. These extremely low spin temperatures can be reached by two-stage adiabatic nuclear demagnetization. Spin ordering has been investigated by employing magnetic susceptibility measurements on copper and silver and by using neutron diffraction techniques on copper. Three antiferromagnetic phases in the field-entropy plane have been discovered in copper, caused by competition between the dipolar and Ruderman-Kittel exchange interactions; only one ordered state has been found in silver. Negative spin temperatures have been produced in silver as well, and a clear ferromagnetic tendency was observed when T < 0. The theoretically calculated spin-spin interactions, ordering temperatures, magnetic phase diagrams and ordered spin structures are in good overall agreement with experimental data for these two metals. 相似文献
2.
Tanmoy Chakraborty Harkirat SinghDiptaranjan Das Tamal K. SenChiranjib Mitra 《Physics letters. A》2012
We report temperature and magnetic field dependent magnetization and quantification of entanglement from the experimental data for dichloro (thiazole) copper (II), a Heisenberg spin chain system. The plot of magnetic susceptibility vs. temperature indicates an infinite spin chain. Isothermal magnetization measurements (as functions of magnetic field) were performed at various temperatures below the antiferromagnetic (AFM) ordering, where the AFM correlations persist significantly. These magnetization curves are fitted to the Bonner–Fisher model. Magnetic susceptibility is used as an entanglement witness to quantify the amount of entanglement in the system. 相似文献
3.
P. Borrmann H. Stamerjohanns E.R. Hilf D. Tománek 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(1):117-119
In contrast to the experimentally widely used isentropic demagnetization process for cooling to ultra-low temperatures we
examine a particular classical model system that does not cool, but rather heats up with isentropic demagnetization. This
system consists of several magnetite particles in a colloidal suspension, and shows the uncommon behavior of disordering structurally
while ordering magnetically in an increasing magnetic field. For a six-particle system, we report an uncommon structural transition
from a ring to a chain as a function of magnetic field and temperature.
Received 5 September 2000 相似文献
4.
A theoretical model is presented in this paper for degree of spin polarization in a light emitting diode (LED) whose epitaxial region contains quantum dots doped with magnetic impurity. The model is then used to investigate the effect of electron–phonon interaction on degree of spin polarization at different temperatures and magnetic fields. It is found that magnetic impurity increases the degree of spin polarization irrespective of temperature, while the electron–phonon interaction decreases the degree of spin polarization. Results are found to be in better agreement with experiments. 相似文献
5.
A. F. Andreev 《Physica B: Condensed Matter》1995,210(3-4):378-382
The melting and growth of 3He crystals spin-polarized by an external magnetic field at temperatures below the Neel temperature are accompanied by spin supercurrents in addition to mass flows. In fields weak in comparison with exchange fields, the crystallization waves change in nature, because the spin currents begin to play a dominent role. The wave spectrum becomes linear with a velocity inversely proportional to the magnetic field. The attenuation of the waves at low enough temperatures is mainly due to the interaction of the moving crystal-liquid interface with thermal spin waves in the crystal. The waves could be weakly damped at temperatures below a few hundred microkelvins. 相似文献
6.
The helicoidal magnetic structure of a MnGe compound doped with 25% Fe is studied by means of small-angle neutron scattering in a wide temperature range of 10–300 K. Analysis of the scattering-function profile demonstrates that magnetic structures inherent to both pure MnGe and its doped compounds are unstable. The doping of manganese monogermanide is revealed to lead to higher destabilization of the magnetic system. In passing from MnGe to Mn0.75Fe0.25Ge, the magnetic-ordering temperature T N decreases from 130 to 95 K, respectively. It is demonstrated that, at temperatures close to 0 K, the intensity of the contribution to scattering from stable spin helices decreases and the intensity of scattering by spin helix fluctuations increases with increasing impurity-metal concentration. An increased intensity of anomalous scattering caused by spin excitations existing in the system is observed. Helicoidal fluctuations and spin excitations corresponding to low temperatures indicate the quantum nature of the instability in the doped compound. However, MnGe doping with Fe atoms has no influence on the compound’s magnetic properties at temperatures of higher than T N. The temperature range of short-range ferromagnetic correlations is independent of concentrations and is restricted by temperatures T ranging from 175 to 300 K. 相似文献
7.
The transformation of the spin structure of a high-spin Fe8 cluster in a strong magnetic field has been investigated. The magnetization and magnetic susceptibility of the material are
calculated at different external magnetic fields and temperatures. It is shown that the magnetic field induces transformation
of the spin structure of a Fe8 cluster from the quasi-ferrimagnetic structure with an average magnetic moment of 20 μB per molecule to the quasi-ferromagnetic structure with a magnetic moment of 40 μB. Unlike a similar transformation of a Néel ferrimagnet, which is continuous and occurs through an intermediate angular phase,
this process in Fe8 at low temperatures manifests itself as a cascade of discrete quantum jumps, each being the transition accompanied by an
increase in the spin number of the complex. At high temperatures, the behavior of the magnetic cluster approaches the cluster
behavior described by the classical theory. The nature of quantum jumps is discussed in terms of the magnetic-field-induced
energy level crossing in the ground state of a magnetic cluster.
__________
Translated from Fizika Tverdogo Tela, Vol. 42, No. 6, 2000, pp. 1068–1072.
Original Russian Text Copyright ? 2000 by Zvezdin, Plis, Popov. 相似文献
8.
V. V. Prudnikov V. N. Borodikhin 《Journal of Experimental and Theoretical Physics》2005,101(2):294-298
Phase transitions in the three-dimensional diluted Ising antiferromagnet in an applied magnetic field are analyzed numerically. It is found that random magnetic field in a system with spin concentration below a certain threshold induces a crossover from second-order phase transition to first-order transition to a new phase characterized by a spin-glass ground state and metastable energy states at finite temperatures. 相似文献
9.
10.
Finite-temperature magnetic properties of iron thin films are investigated by computer simulation over a broad range of temperatures up to the point of the ferromagnetic–paramagnetic phase transition. The coupled dynamics of atoms and magnetic moments is treated using the large-scale spin–lattice dynamics (SLD) algorithm. We investigate surface and bulk magnetic properties of iron, and how these properties vary as a function of temperature, film thickness and surface crystallography. We find that magnetization at surfaces is enhanced at low temperatures and suppressed at higher temperatures, in agreement with experimental observations. The effective Curie temperature of a film decreases as a function of thickness. Short-range magnetic order and non-vanishing spin–spin spatial correlations are found above the Curie temperature. The spin autocorrelation functions exhibit slower oscillations with longer decoherence times near the surface. We also find that the directional spin disorder has a significant effect on the surface strain. 相似文献
11.
In this study the authors use the negativity to study the entanglement of electronic spin and thermally induced subband states
inside a quasi-one-dimensional Rashba nanowire (of width in the order of 100 nm), to which a perpendicular uniform magnetic
field is applied. To be clearer, it is assumed that the nanowire is held at a temperature T, so that all subband excitations,
with definite probabilities, are present. The partially transposed density matrix is shown to be block-diagonal whose eigenvalues
are readily obtained. It is shown that at least one of the eigenvalues is always negative, so that the system of electronic
spin and subbands inside a Rashba nanowire is never separable. Moreover, it is shown that the negativity, at certain temperatures,
exhibits maxima. The temperatures at which the entanglement is maximal strongly depend on the magnetic field. The authors
further present graphs of negativity, as functions of temperature, for different magnetic fields, indicating how this agent
may be used to control the spin-subband entanglement. 相似文献
12.
Ekrem Aydiner Yusuf Yüksel Hamza Polat 《Journal of magnetism and magnetic materials》2009,321(19):3193-3197
In this study, dependence on site dilution of critical and compensation temperatures of a two-dimensional mixed spin-1/2 and spin-1 system has been investigated with Monte Carlo simulation. The dependence of the thermal and magnetic behaviors on dilution of mixed spin system has been discussed. We have shown that the critical and compensation temperatures of diluted mixed spin system linearly decrease with increasing number of diluted sites. 相似文献
13.
Jaime M Correa VF Harrison N Batista CD Kawashima N Kazuma Y Jorge GA Stern R Heinmaa I Zvyagin SA Sasago Y Uchinokura K 《Physical review letters》2004,93(8):087203
Besides being an ancient pigment, BaCuSi2O6 is a quasi-2D magnetic insulator with a gapped spin dimer ground state. The application of strong magnetic fields closes this gap, creating a gas of bosonic spin triplet excitations. The topology of the spin lattice makes BaCuSi2O6 an ideal candidate for studying the Bose-Einstein condensation of triplet excitations as a function of the external magnetic field, which acts as a chemical potential. In agreement with quantum Monte Carlo numerical simulations, we observe a distinct lambda anomaly in the specific heat together with a maximum in the magnetic susceptibility upon cooling down to liquid helium temperatures. 相似文献
14.
Evangelisti M Candini A Ghirri A Affronte M Powell GW Gass IA Wood PA Parsons S Brechin EK Collison D Heath SL 《Physical review letters》2006,97(16):167202
We report on the Fe17 high-spin molecular cluster and show that this system is an exemplification of nanostructured dipolar magnetism. Each Fe17 molecule, with spin S=35/2 and axial anisotropy as small as D approximately -0.02 K, is the magnetic unit that can be chemically arranged in different packing crystals while preserving both the spin ground state and anisotropy. For every configuration, molecular spins are correlated only by dipolar interactions. The ensuing interplay between dipolar energy and anisotropy gives rise to macroscopic behaviors ranging from superparamagnetism to long-range magnetic order at temperatures below 1 K. 相似文献
15.
16.
通过分析不同温度下HgMnTe磁性二维电子气Shubnikov-de Hass(SdH)振荡的拍频现象,研究了量子阱中电子自旋 轨道相互作用和spd交换相互作用.结果表明:(1)在零磁场下,电子的自旋 轨道相互作用导致电子发生零场自旋分裂;(2)在弱磁场下,电子的自旋-轨道相互作用占主导地位,并受Landau分裂和Zeeman分裂的影响,电子的自旋分裂随磁场增加而减小;(3)在高磁场下,电子的spd交换相互作用达到饱和,电子的自旋分裂主要表现为Zeeman分裂.实验证明了当电子的Zeeman分裂能量与零场
关键词:
磁性二维电子气
Zeeman分裂
Rashba自旋分裂 相似文献
17.
An Ising effective field theory model is presented to calculate the magnetic properties of 2D nano-islands on a nonmagnetic substrate, subject to an externally out-of-plane applied magnetic field. The system Hamiltonian contains nearest neighbor exchange interactions, single-atom magnetic anisotropies, and the Zeeman term. The calculations yield, in particular, the single site spin correlations, the magnetizations, and the isothermal susceptibilities, for the core and periphery domains of the nano-island. The choice of a spin S=1 for the atoms of the system permits the analysis of local spin fluctuations via the single site spin correlations. We investigate in this respect the effects due to the different magnetocrystalline anisotropies and reduced dimensionalities, for the core and periphery domains, and in particular the critical influence of the applied magnetic field. Detailed theoretical results are presented for the square and hexagonal lattice symmetries, with numerical applications for the 2D monolayer Co nano-islands on a Pt substrate. It is shown that the remarkable differences between the magnetic properties of the core and periphery domains in zero field are washed out when an out-of-plane field is applied. The applied field also provokes critical discontinuities for the spin correlations and magnetization reversals, for the core and periphery domains, which are especially evident for the hexagonal lattice nano-island in the range of fields of interest. The discontinuities and magnetization reversals occur over elementary temperature widths, and shift to lower temperatures with increasing field. The field-dependant isothermal susceptibilities show new features very different from those for the susceptibilities in zero field. The present Ising model does not show any blocking temperature transition to superparamagnetism. 相似文献
18.
Haverkort MW Hu Z Cezar JC Burnus T Hartmann H Reuther M Zobel C Lorenz T Tanaka A Brookes NB Hsieh HH Lin HJ Chen CT Tjeng LH 《Physical review letters》2006,97(17):176405
Using soft x-ray absorption spectroscopy and magnetic circular dichroism at the Co-L(2,3) edge, we reveal that the spin state transition in LaCoO3 can be well described by a low-spin ground state and a triply degenerate high-spin first excited state. From the temperature dependence of the spectral line shapes, we find that LaCoO3 at finite temperatures is an inhomogeneous mixed-spin state system. It is crucial that the magnetic circular dichroism signal in the paramagnetic state carries a large orbital momentum. This directly shows that the currently accepted low- or intermediate-spin picture is at variance. Parameters derived from these spectroscopies fully explain existing magnetic susceptibility, electron spin resonance, and inelastic neutron data. 相似文献
19.
N. Yu. Pankratov A. I. Zvonov D. Yu. Karpenkov A. I. Smarzhevskaya A. Yu. Karpenkov S. A. Nikitin 《Bulletin of the Russian Academy of Sciences: Physics》2013,77(10):1268-1271
The magnetocaloric effect of rare-earth metals (REMs) Gd, Tb, and Dy in the nanostructured state is investigated. The ranges of working temperatures and cool capacity for materials based on nanocrystalline REMs are calculated from the experimental data. These results enable us to evaluate in detail the magnetic properties of REMs in a nanocrystalline state. It is shown that nanocrystalline Dy possesses the largest cool capacity, making this material most effective for magnetic cooling in the temperature range of 82–134 K. 相似文献