Thermodynamic geometry of a kagome Ising model in a magnetic field

We derived the thermodynamic curvature of the Ising model on a kagome lattice under the presence of an external magnetic field. The curvature was found to have a singularity at the critical point. We focused on the zero field case to derive thermodynamic curvature and its components near the criticality. According to standard scaling, scalar curvature R   behaves as |β−_βc|^α−2${|\beta -{\beta }_c|}^{\alpha -2}$ for α>0$\alpha >0$ where β is the inverse temperature and α is the critical exponent of specific heat. In the model considered here in which α is zero, we found that R   behaves as |β−_βc|^α−1${|\beta -{\beta }_c|}^{\alpha -1}$.     

Thermodynamic properties of solid naphthalene: Cell model and quasiharmonic calculations

Cell model and quasihannonic calculations have been made for solid naphthalene, using the atom-atom approximation for intermolecular interactions. Throughout the temperature range examined (78–323 K) the cell model is found to be superior to the quasiharmonic approximation in describing the basic thermodynamic functions of the crystal. An attempt is also made to extend the cell model to calculate the elasticity tensor and thermal expansion.     

Dynamical properties of the 2D wigner crystal in a strong magnetic field

Summary The dispersion relations and the shear modulus of the 2D Wigner crystal (WC) in the presence of a strong magnetic field are evaluated using a density functional method which includes the effect of electronic correlations. Comparison is made with previous theoretical results on the magnetophonons and the shear modulus. The effect of correlation on the stability of the crystal is discussed. In honour of Prof. Fausto Fumi on the occasion of his retirement from teaching.     

Hybridisation and crystal field in YbPd2Si2

Experimental data in the hybridized compound YbPd₂Si₂ is compared with the results obtained with a recently proposed hybridisation model, based on the large-degeneracy expansion approximation, which takes into account the crystal field splittings of the rare earth ion energy levels. With a unique set of parameters, satisfactory agreement is simultaneously obtained for the thermal variation of the electronic specific heat, of the magnetic susceptibility and of the electric field gradient at the Yb site, as well as for the field variation of the low temperature magnetisation.     

Crystal field and magnetic properties of the tetragonal TbNi2Si2 compound

The magnetic properties of a TbNi₂Si₂ single crystal have been investigated experimentally by specific heat, anisotropy of the susceptibility and magnetization, and inelastic neutron scattering, leading to the determination of its fundamental coupling parameters. The lowest crystalline electric field states are two singlets close to each other, that explains the different magnetic structures evidenced in TbNi₂Si₂: an amplitude modulated structure, close to T _N , a simple antiferromagnetic one at low temperature and an antiphase one when an external magnetic field is applied along the c direction.     

弱磁场中弱相互作用费米气体的热力学性质

根据赝势法和系综理论导出弱磁场中弱相互作用费米气体的内能、化学势和热容量的小参数r的解析式.在此基础上给出高温和低温两种情况下弱磁场中弱相互作用费米气体的热力学性质,探讨磁场及粒子间相互作用对热力学性质的影响,分析磁场与三维谐振势两种约束对系统性质影响的不同及其原因. 关键词： 赝势法 费米气体 相互作用 热力学性质     

Magnetic properties of the bond and crystal field dilution Blume-Emery-Griffiths model in the presence of magnetic field

The magnetic properties of the spin-1 bond and crystal field dilution Blume-Emery-Griffiths (BEG) model in the presence of magnetic field are investigated on a simple cubic lattice by using effective field theory (EFT). In the M-H plane, the common action of bond and crystal field dilution leads to the exhibition of an irregular initial magnetization curve and slows down the magnetization process. The peak of the susceptibility curve has an explicit decline and shows a distinct shift toward the direction of increase of magnetic field. On the other hand, in the M-T plane, the magnetization curves show a discontinuity and a vertical leap in the small range of magnetic field when the negative crystal field is larger and the ratio of biquadratic and exchange interaction is positive (α>0). These results have not been revealed in previous works.     

弱磁场中弱相互作用玻色气体的热力学性质

运用外势中弱相互作用玻色体系的理论结论,研究弱磁场中弱相互作用玻色气体的高温热力学性质,给出系统总能和热容量的解析式,分析粒子之间的相互作用及磁场对系统热力学性质的影响.研究结果表明,排斥(吸引)对粒子和能量的空间分布有集中(分散)作用,并使得系统的化学势、总能、热容量都增大(减小);加强磁场既可使得粒子和能量的空间分布趋于分散又可削弱相互作用对粒子和能量空间分布的影响.相互作用对各个特征量的影响也有着不同的个性表现.     

强磁场中弱相互作用费米气体的热力学性质

基于赝势法和局域密度近似研究了强磁场中弱相互作用费米气体的热力学性质,得出化学势、总能和热容量的解析式,同时分析了磁场及相互作用对系统热力学性质的影响.研究表明,无论是高温情况还是低温情况下,磁场都能调节相互作用的影响.低温下,与无磁场的系统相比,磁场降低系统的化学势、总能和热容量;与无相互作用系统相比,排斥作用增加化学势而降低总能及热容量.高温下,磁场和排斥作用均可降低系统的总能而增加热容量,强磁场可以改变相互作用对总能及热容量的影响. 关键词： 强磁场 弱相互作用 费米气体 热力学性质     

Magnetic ordering in HoRu2Si2, HoRh2Si2, TbRh2Si2 and TbIr2Si2 by neutron diffraction

Neutron diffraction study of polycrystalline HoRu₂Si₂, HoRh₂Si₂, TbRh₂Si₂, and TbIr₂Si₂ was performed in the temperature range between 4.2 and 300 K. For HoRu₂Si₂ the magnetic spin alignment of a linear transverse wave mode below the Néel temperature 19 K is observed. This static moment wave is propagating along the b-axis with k=(0, 0.2, 0) and is polarized in the c-axis. The root-mean-square and maximum saturation moments per Ho atom are 9.26 and 13.09μ_B, respectively. HoRh₂Si₂, TbRh₂Si₂ an TbIr₂Si₂ are simple collinear antiferromagnets of +-+- type with Néel temperatures of (27±1), (98±2) and (72±3) K, respectively. For TbRh₂Si₂ and TbIr₂Si₂ magnetic moments are localized on RE ions only and are aligned along the tetragonal axis, while for HoRh₂Si₂ they form an angle ø = (28±3)°.     

Frequency effects in capacitively coupled radio-frequency glowdischarges: a comparison between a 2-D fluid model and experiments

The results of a 2-D fluid model for argon radiofrequency (RF) discharges in a closed cylindrical vacuum chamber are compared with experimental data from an amorphous silicon deposition reactor operated in argon. Good agreement is obtained for the relation between the DC autobias voltage and the dissipated power in the frequency range 40-100 MHz at pressures between 10 and 60 Pa. Scaling laws are presented for the dissipated power and for the ion fluxes toward the electrodes. These quantities are expressed in the DC bias voltage, the RF excitation frequency and the background pressure. Also the uniformity of the ion fluxes is studied. The model yields a linear relation between the applied RF voltage and the DC bias voltage. This relation depends only on the geometry of the discharge chamber and shows an offset     

Thermodynamic properties of the spin-1/2 antiferromagnetic ladder under magnetic field

Specific heat (C_V) measurements in the spin-1/2 Cu₂(C₂H₁₂N₂)₂Cl₄ system under a magnetic field up to H =8.25 T are reported and compared to the results of numerical calculations based on the 2-leg antiferromagnetic Heisenberg ladder. While the temperature dependences of both the susceptibility and the low-field specific heat are accurately reproduced by this model, deviations are observed above the critical field H_C1 at which the spin gap closes. In this Quantum High Field phase, the contribution of the low-energy quantum fluctuations are stronger than in the Heisenberg ladder model. We argue that this enhancement can be attributed to dynamical lattice fluctuations. Finally, we show that such a Heisenberg ladder, for H > H C1, is unstable, when coupled to the 3D lattice, against a lattice distortion. These results provide an alternative explanation for the observed low temperature ( K-0.8 K) phase (previously interpreted as a 3D magnetic ordering) as a new type of incommensurate gapped state. Received: 23 July 1998 / Accepted: 24 August 1998     

The determination of crystal field levels in the intermetallic compound HoRh by inelastic neutron scattering

Inelastic neutron time of flight measurements have been carried out on the intermetallic compound HoRh at different temperatures. Well resolved transitions between crystal field levels were observed at 4.0 and 9.7 meV. The complete crystal field level scheme was deduced and the crystal field parameters were found to be A₄⁰ 〈r⁴〉 = ?10.98 meV and A₆⁰ 〈r⁶〉 = ?1.59 meV. These values deviate considerably from point charge estimates.     

Interpretation of Kondo experiments in a magnetic field

Thermodynamical properties of the “resonance level model” are calculated for arbitrary spin and magnetic field. Assuming this model to describe the basic physics of the Kondo problem we find a satisfactory agreement with recent magnetization data on $\text{Ag}$Fe.     

Mg2Si晶体结构及消光特性的研究

基于高能X射线的散射理论,研究了Mg₂Si晶体的结构和消光特性.结果表明,Mg₂Si晶体具有反萤石结构,当衍射指数H,K和L奇偶混合时其散射光就会出现系统消光,而当衍射指数H,K和L全为偶数或者全为奇数时,其散射光就会出现衍射.在实际应用中对研究具有反萤石结构的晶体具有重要意义. 关键词： 散射理论 消光特性 反萤石结构 衍射     

Thermodynamic characteristics of Fermi gases in a magnetic field

Within the framework of statistical thermodynamics of equilibrium systems, general expressions are obtained for the chemical potential, pressure, and magnetic susceptibility for degenerate ideal nonrelativistic electron, proton, and neutron gases in magnetic fields, which exert no pronounced influence on the anomalous magnetic moments of the fermions.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 21–25, May, 1987.     

Thermodynamic functions of a two-sublattice ferrite in a magnetic field

This paper considers the effect of the magnetic field on the specific heat, entropy, and temperature behavior of the magnetization in a two-sublattice ferrite in the collinear phase. It is shown that the specific heat and entropy vary nonmonotonically with the magnetic field, while at low temperatures the magnetization increases with the temperature when the magnetic field takes values in the range H₁/2 < H h₁, where H₁ is the value of the magnetic field for which deviation from the collinear structure begins [1, 2].Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 33–36, January, 1977.In conclusion, the author wishes to express his indebtedness to G. M. Nedlin and to thank him for his valuable appraisal of the work.