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1.
We present an analysis of the thermodynamic properties of small transition-metal clusters and show how the commonly used indicators of phase transitions such as peaks in the specific heat or magnetic susceptibility can lead to deceptive interpretations of the underlying physics. The analysis of the distribution of zeros of the canonical partition function in the whole complex temperature plane reveals the nature of the transition. We show that signals in the magnetic susceptibility at positive temperatures have their origin at zeros lying at negative temperatures.  相似文献   

2.
陈凌孚  王强华 《物理学报》1989,38(5):840-845
本文提出具有非磁性缺陷(nm1/2l<<1)的二维RKKY自旋玻璃模型,分别给出不同温区比热和磁化率的表达式.同时应用渗流理论分析转变温区自旋集团的行为,说明比热膝盖伏峰值和磁化率尖拐状峰值的实验事实. 关键词:  相似文献   

3.
Vibration modes and thermodynamic properties of a body‐centered cubic (bcc) Coulomb crystal with a small admixture of substitutional isotopic impurities are studied analytically applying the perturbation theory of disordered crystal spectra and the Lifshitz‐Krein trace formula. We calculate the density of phonon states of the perfect bcc Coulomb crystal and use it to compute the heat capacity of the crystal with impurities in a wide range of temperatures. It is shown that the ratio of an impurity contribution to the crystal heat capacity over the perfect crystal specific heat tends to a constant in the low‐temperature quantum regime and decays as T–2 in the classic regime of high temperatures. It is also shown that even a small concentration of heavy impurities amplifies significantly the total crystal heat capacity. The results are compared with those obtained using the more conventional linear mixing theory. It is demonstrated that both methods give similar results at all tempera‐tures when the impurity mass is not too different from that of the base ions but a strong discrepancy is observed at low and intermediate temperatures when impurities are noticeably lighter or heavier. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

4.
When a dilute alloy exhibits exchange enhancement of the isolated impurity susceptibility, it is shown that pairs of impurities may exhibit a low lying anti-parallel fluctuation mode such that the pair susceptibility in a uniform field is less enhanced than that of the isolated impurity, while the specific heat may be strongly enhanced. N.M.R. properties of such a pair should exhibit a small shift in frequency and a fast nuclear spin lattice relaxation time, leading to possibly large deviations from the Korringa relation.  相似文献   

5.
The random field Ising model is studied numerically at both zero and positive temperature. Ground states are mapped out in a region of random field and external field strength. Thermal states and thermodynamic properties are obtained for all temperatures using the Wang-Landau algorithm. The specific heat and susceptibility typically display sharp peaks in the critical region for large systems and strong disorder. These sharp peaks result from large domains flipping. For a given realization of disorder, ground states and thermal states near the critical line are found to be strongly correlated--a concrete manifestation of the zero temperature fixed point scenario.  相似文献   

6.
Recently it has been shown by analysing Mössbauer spectra of dilute alloys of iron in gold that the anisotropic part of the exchange interaction between iron near neighbours determines the direction of magnetisation of such iron moments at low temperatures. Estimates of the important interactions between moments, which are here identified as the isotropic and anisotropic parts of the near neighbour exchange, and the isotropic exchange between further neighbours via the conduction electrons, have been obtained from available experimental data. The near neighbour exchange causes spins within random clusters linked as near neighbours to align parallel (the isotropic part) and to prefer certain directions in the cluster (the anisotropic part). The further neighbour exchange is responsible for the cooperative magnetic transition shown in Mössbauer and small field susceptibility results. The final model leads to qualitative interpretations of the temperature and field dependence of the susceptibility, and is able to reproduce the hysteresis loops observed at low temperatures for samples cooled in different fields. The effects of the interactions on the entropy and specific heats are discussed, and it is shown that the linear specific heat contributions at low temperatures occur because of the anisotropic interactions.  相似文献   

7.
Measurements of the depressions of the superconducting transition temperature Tc with Sm impurity concentration and the specific heat jump at Tc as a function of Tc, and the temperature dependences of the normal state specific heat and magnetic susceptibility are reported for the matrix impurity system (LaSm)Sn3. The results constitute the first definitive evidence of a Kondo effect for a dilute alloy containing Sm impurities.  相似文献   

8.
A model of iron/vanadium superlattice has been proposed to study the phase transition in multilayers. The temperature dependences of the magnetization, susceptibility, and specific heat have been obtained. Two specific heat peaks are revealed at small ratios between the interlayer and intralayer exchanges.  相似文献   

9.
The gamma-->alpha isostructural transition in the Ce0.9-xLaxTh0.1 system is measured as a function of La alloying using specific heat, magnetic susceptibility, resistivity, thermal expansivity or striction measurements. A line of discontinuous transitions, as indicated by the change in volume, decreases exponentially from 118 K to close to 0 K with increasing La doping, and the transition changes from being first-order to continuous at a critical concentration, x(c) approximately 0.14. At the tricritical point, the coefficient of the linear T term in the specific heat gamma and the magnetic susceptibility increase rapidly near x(c) and approach large values at x=0.35 signifying that a heavy Fermi-liquid state evolves at large doping. The Wilson ratio reaches a value above 2 for a narrow range of concentrations near x(c), where the specific heat and susceptibility vary most rapidly with the doping concentration.  相似文献   

10.
Finite chains of a two-state random Potts spin model with periodic boundary conditions are studied within Glauber dynamics. The spin exchange is assumed random with frustration between ferro and antiferromagnetic values (±J). Time-dependent fluctuations are induced by periodic temperature oscillations. Master type differential equations for spin correlation functions are solved within linear response theory. The spectrum of relaxation times are calculated at different temperatures. The ±J Potts glass chains undergo a zero temperature phase transition. The barriers against inversion of the spin chain take only two values; 0 and 2|J|. The temperature behaviour of specific heat is characterized by rounded peaks. The frequency dependence displays two plateaus for the real part of specific heat and two corresponding peaks for the imaginary part. The dynamic specific heat is not affected by the longest relaxing mode like susceptibility. The time separation of the modes is demonstrated by the Cole-Cole plots.  相似文献   

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