共查询到20条相似文献,搜索用时 15 毫秒
1.
R. R. Gareev D. E. Bü rgler M. Buchmeier R. Schreiber P. Grü nberg 《Journal of magnetism and magnetic materials》2002,240(1-3):235-237
Fe/Fe1−xSix/Fe (x=0.4–1.0) wedge-type epitaxial trilayers with improved homogeneity are grown by co-evaporation from two electron-beam sources. The coupling strengths of the bilinear (J1) and biquadratic (J2) coupling terms are derived from Brillouin light scattering (BLS) spectra and longitudinal MOKE hysteresis loops. The total coupling strength J=J1+J2 increases dramatically with increasing x and reaches values in excess of 6 mJ/m2. 相似文献
2.
本文用实空间重整化群方法讨论了准周期层状铁磁超晶格的磁自旋波,用Reduce语言推导了decimation变换公式,从而求得了局域格林函数、局域态密度和约化磁矩。发现局域态密度的带宽和约化磁矩与最近邻相互作用J1、J2及格点自旋sa、sb密切相关。 相似文献
3.
M. Hamedoun M. Houssa N. Benzakour A. Hourmatallah 《Physica B: Condensed Matter》1999,270(3-4):384-390
By making use of high-temperature series expansions (HTSE) of the correlation functions, we study the thermal and disorder variation of the short-range order (SRO) in the particular B-spinel ZnCr2xAl2−2xS4. We developed the HTSE for the q-dependent static structure factor S(q) to the order 6 in reciprocal temperature including both the nearest- and next-nearest-neighbour interactions J1 and J2, respectively. Respecting the experimental fact that the broad diffuse peak of the neutron is situated at the particular wave vector q0=[0 0 0.79] and is insensitive to the temperature for a given ratio of dilution x, we have estimated the thermal variation of J1 and J2 in the case of the pure compound.
The bond percolation threshold xp of the ZnCr2xAl2−2xS4 is determined by studying the disorder variation of the correlation length ξ. The xp is considered as the concentration at which ξ vanishes. The obtained values are xp=0.27 when only J1 is considered and 0.23 when both J1 and J2 are taken into account. 相似文献
4.
Ai-Yuan Hu Lin Wen Guo-Pin Qin Zhi-Min Wu Peng Yu Yu-Ting Cui 《Frontiers of Physics》2019,14(5):53601
The frustrated spin-1/2 J1a–J1b–J2 antiferromagnet with anisotropy on the two-dimensional square lattice was investigated, where the parameters J1aand J1b represent the nearest neighbor exchanges and along the x and y directions, respectively. J2 represents the next-nearest neighbor exchange. The anisotropy includes the spatial and exchange anisotropies. Using the double-time Green’s function method, the effects of the interplay of exchanges and anisotropy on the possible phase transition of the Néel state and stripe state were discussed. Our results indicated that, in the case of anisotropic parameter 0≤η<1, the Néel and stripe states can exist and have the same critical temperature as long as J2 = J1b/2. Under such parameters, a first-order phase transformation between the Néel and stripe states can occur below the critical point. For J2 ≠J1b/2, our results indicate that the Néel and stripe states can also exist, while their critical temperatures differ. When J2>J1b/2, a first-order phase transformation between the two states may also occur. However, for J2<J1b/2, the Néel state is always more stable than the stripe state. 相似文献
5.
The surface roughness dependence of the first-order probability density function (PDF) of an integrated speckle pattern, produced in the condition of circular detection aperture and gaussian scattering spot, was theoretically investigated. The mutual intensity JA(x1, y1; x2, y2) containing two roughness parameters, dispersion of surface height ø2 lateral correlation length xc, was calculated. The exact first-order probability density function was analytically derived and numerically calculated by means of the Karhunen-Loeve expansion and fast Fourier transform (FFT). As a diffuse object became smooth, the first order probability density function was changed from negative exponential to sharp peak gaussian centered around mean intensity. 相似文献
6.
Within a real-space renormalization-group framework, we approach the cubic lattice through a D = 3 diamond-like hierarchical lattice. The model is a standard, nearest-neighbor, Ising spin glass with coupling constants {Jij} distributed according to the family of continuous probability distributions Pq(Jij) ∝ 1/[1 + (q − 1)Jij2/2J2]1/(q − 1) (if 1 + (q − 1) Jij2/2J2 > 0, and zero otherwise; q
). Such distributions, which arise naturally in the treatment, within the recently proposed nonextensive thermostatistics, of anomalous diffusion, reproduce the usual, Gaussian case, for q → 1. Moreover, they present a second moment Jij2 proportional to (5 − 3q)−1 for q < 5/3, diverging for q ≥ 5/3, but keeping a finite width at midheight. In the limit q → 3, Pq(Jij) collapses with the abscissa, and so the width at midheight diverges. We compute the q-dependence of the spin-glass critical temperature Tc. We show numerically that Tc does not scale with Jij21/2 (contrary to the usual belief), but rather with the width at midheight of Pq(Jij). Our results suggest that Tc vanishes as −1/q when q → −∞; furthermore, we verified that Tc diverges exponentially when q approaches 3 from below. 相似文献
7.
We have measured the resistivity of textured Bi1.84Pb0.4Sr2Ca2Cu3Oy silver-clamped thick films as a function of temperature, current density ranging from 10 to 1×103 A/cm2 and magnetic field up to 0.3 T. We find that the effective activation energy Ue follows Ue(T,J,H)=U0(1−T/Tp)mln(Jc0/J)H− with m=1.75 for Hab-plane and 2.5 for Hc-axis and =0.76 for Hab and 0.97 for Hc, for the current density regime above 100 A/cm2, where Tp is a function of applied magnetic field and current density. This result suggests the effective activation energy Ue be correlated with the temperature, current density and magnetic field. The possible dissipative mechanisms responsible for the temperature, current density and magnetic field dependence of the effective activation energy are discussed. 相似文献
8.
《Journal of magnetism and magnetic materials》1989,80(2-3):183-188
This paper gives an analysis of the high temperature susceptibility of diluted semimagnetic-semiconductor Zn1 − xMnxS. The high-temperature susceptibility of Zn1 − xMnxS was found to behave in accordance with the Curie-Weiss law. From χ(T) measurements the exchange integral of Mn2+ -Mn2+ interaction 2J1/kB = (-34.6±0.5) K (effective exchange integral) was obtained. A spin S = 2.6±0.1, close to its atomic value S =
, was also found. The role of the superexchange in this alloy is shortly discussed at the end of the paper. 相似文献
9.
We argue that it is the hopping transport that is responsible for broadening of the σxx peaks. Explicit expressions for the width Δν of a peak as a function of the temperature T, current J and frequency ω are found. It is shown that Δν grows with T as (T/T1)κ, where κ is the inverse localization-length exponent. The current J is shown to act like the effective temperature Teff(J) ∝ J1/2 if
. Broadening of the ohmic ac-conductivity peaks with frequency ω is found to be determined by the effective temperature 相似文献
10.
Hua-Xing Chen 《理论物理通讯》2022,74(12):125201
After examining Feynman diagrams corresponding to the ${\bar{D}}^{(* )}{{\rm{\Sigma }}}_{c}^{(* )}$, ${\bar{D}}^{(* )}{{\rm{\Lambda }}}_{c}$, ${D}^{(* )}{\bar{K}}^{* }$, and ${D}^{(* )}{\bar{D}}^{(* )}$ hadronic molecular states, we propose a possible binding mechanism induced by shared light quarks. This mechanism is similar to the covalent bond in chemical molecules induced by shared electrons. We use the method of QCD sum rules to calculate its corresponding light-quark-exchange diagrams, and the obtained results indicate a model-independent hypothesis: the light-quark-exchange interaction is attractive when the shared light quarks are totally antisymmetric so they obey the Pauli principle. We build a toy model with four parameters to formulize this picture and estimate binding energies of some possibly-existing covalent hadronic molecules. A unique feature of this picture is that the binding energies of the (I)JP = (0)1+ $D{\bar{B}}^{* }/{D}^{* }\bar{B}$ hadronic molecules are much larger than those of the (I)JP = (0)1+ ${{DD}}^{* }/\bar{B}{\bar{B}}^{* }$ ones, while the (I)JP = (1/2)1/2+ $\bar{D}{{\rm{\Sigma }}}_{c}/\bar{D}{{\rm{\Sigma }}}_{b}/B{{\rm{\Sigma }}}_{c}/B{{\rm{\Sigma }}}_{b}$ hadronic molecules have similar binding energies. 相似文献
11.
Discussion Compton scattering on the new states we establish the following: The spin JP = 2+ state, an orbital excitation of ψ, must exist, and its coupling to the ψ(3084) is related to the coupling ψX(2800). A spin higher than 2 (probably 3) with negative charge conjugation must exist, and its couplings can be related to the ψ2+γ and ψ′2+γ couplings. This state might have a substantial radiative width to the 2+. These results depend on a saturation assumption of the sum rules, which has always worked well. Its failure will also be of interest. 相似文献
12.
P. J. Kung P. G. Wahlbeck M. E. McHenry M. P. Maley D. E. Peterson 《Physica C: Superconductivity and its Applications》1994,220(3-4):310-322
Silver-sheathed TlBa2Ca2Cu3O9+δ (Tl-1223) tapes, with a transport critical current density, Jct, of 6200 A/cm2 at 75 K under zero magnetic field, were fabricated by the oxide-powder-in-tube (OPIT) method and characterized using an X-ray diffractometer (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), and superconducting quantum interference device (SQUID) magnetometer. The results of the magnetization and SEM study indicate that, in these tapes, individual grains are distributed randomly in orientation and weak links exist. However, strongly linked percolative current paths within the tape persisting in increasing fields, accompanied by strong intrinsic interplanar coupling, sustain a significant Jct at high fields and lead to the plateau in the Jct-H curve. Dislocation networks, which may act as effective pinning centers, are the common features observed in the tapes. To investigate the effects on flux pinning due to thermomechanical processing, magnetic relaxation at 1 and 2 T over 5–50 K was measured. The tape shows slightly lower normalized relaxation rates (S=-(1/Mo)dM/ dln t) than the cauliflower-like precursor powder. Analyses of the relaxation data obtained from the tape, after incorporating temperature dependence and field scaling, yield an expression for the effective pinning energy Ueff(J,T,H) = (U1/H0.54)[1-(T/ 72.5)2]4(J/Ji)μ. This result was compared with the prediction of the collective flux-creep model, which suggests that Tl-1223 has a three-dimension-like (3D-like) vortex lattice. Presumably, a more plate-like powder morphology may result in improved texturing by the OPIT process. Tl0.5Bi0.5Sr2CaCu2O7+δ ((Tl,Bi)-1212) powder with this morphology was therefore synthesized for comparison. 相似文献
13.
14.
Phonon anomalies have been reported in iron-pnictide superconductors indicating a diverse interplay between different orders in the materials.Here,we report Raman scattering measurements on Sr(Fe1-xCox)2As2(x=0 and x=0.04)single crystals in the B;symmetry with respect to a 1 Fe unit cell.Upon cooling,we observe a larger split(13 cm;)of Eg Raman phonon modes pertaining to in-plane Fe and As displacements as the crystals undergo the tetragonal-toorthorhombic structural phase transition,although a considerable split(9 cm;)has been reported in BaFe1-xCox)2As2.Furthermore,the splitting of E;phonon modes is strongly reduced upon doping.We perform an order-parameter analysis revealing a similar doping dependence of E;phonon splitting as reported in other compounds of the 122 family,indicating these phonon anomalies widely exist in 122 iron-based superconductors and might share the same mechanisms. 相似文献
15.
16.
A simple, new type of correlated wave function is proposed for the studies of normal two-electron atomic systems: ψ(r1, r2) = ΣcmΦm(r1, r2) with Φm(r1, r2) = exp[−(r1 + r2)]/(br12 + a)m, where , a, b are non-linear variational parameters. A notable feature of this basis function is that only three terms are required within the framework of the Raleigh-Ritz variational principle to obtain fairly accurate energy eigenvalues and satisfactory cusp conditions. The non-linear variational parameters are optimised by using the Monte Carlo technique. 相似文献
17.
A. Oota H. Matsui M. Funakura J. Iwaya K. Mitsuyama 《Physica C: Superconductivity and its Applications》1993,210(3-4):489-501
The influence of the sintering conditions on the microstructure and critical current density Jc has been studied on screen-printed Ag-(Bi, Pb)2Sr2Ca2Cu3Ox tapes with a ceramics mono-layer core. Three kinds of fabrication processes, which consist of a combination of cold working (rolling and/or pressing) and sintering, are applied. Four times repetition of pressing and sintering after the pre-sintering produces the highest c-axis alignment and achieves Jc= 1.5 × 104 A/cm2 (77 K, 0 T). The Jc versus θ data with an angle θ between B and the c-axis elucidate the relation between the anisotropy ratio γ=Jc(Bc)/Jc(B|c and the half-height angular width Δθ of a peak for Bc. This is related to both grain alignment and the Jc value. An increase in Jc, which comes from an improvement for grain alignment, enhances γ and narrows Δθ. The Jc versus θ data are fitted to the expression Jc(B, θ)=J c(B, 90°)/[(γ−1)|cos θ|n+1] by regarding both γ and n as adjustable parameters. Fabrication of screen-printed tapes with multilayers (1≤N≤5) is presented, where the critical current increases from 8.0 A to 30.2 A at 77 K and 0 T as N increases. 相似文献
18.
Partha Guha 《Journal of Geometry and Physics》2003,46(3-4):231-242
It is known that the Korteweg–de Vries (KdV) equation is a geodesic flow of an L2 metric on the Bott–Virasoro group. This can also be interpreted as a flow on the space of projective connections on S1. The space of differential operators Δ(n)=∂n+u2∂n−2++un form the space of extended or generalized projective connections. If a projective connection is factorizable Δ(n)=(∂−((n+1)/2−1)p1)(∂+(n−1)/2pn) with respect to quasi primary fields pi’s, then these fields satisfy ∑i=1n((n+1)/2−i)pi=0. In this paper we discuss the factorization of projective connection in terms of affine connections. It is shown that the Burgers equation and derivative non-linear Schrödinger (DNLS) equation or the Kaup–Newell equation is the Euler–Arnold flow on the space of affine connections. 相似文献
19.
用密度泛函理论的B3LYP方法,分别以6-311++g(df,3pd),6-311g(3d,3p)和6-311++g(3df,3pd)为基函数对NF分子、NF+和NF-离子基态进行几何优化和频率计算,并进行单点能扫描计算.用最小二乘法拟合得到NFX(X=-1,0,+1)分子离子基态的Murrell-Sorbie势能函数.利用得到的解析势能函数计算出的NF分子和NF+离子基态光谱常数(Be,αe,ωe,ωeχe)与实验值符合很好.首次得到NF-离子基态的光谱常数(Be,αe,ωe,ωeχe)和力常数(f2,f3,f4),为NF-离子基态的后期研究提供理论参考. 相似文献
20.
用Vlasov-Poisson方程对相对论电子束在单板、双板间的传播过程进行了数值模拟,给出了单板模型空间电荷积累最大的位置,不同位置上的电流J、电子数密度n、电场E的振荡频率随入射电子数密度n0、入射速度v0的变化关系,双板模型空间电荷积累最大的位置,J、n、E的振荡频率随入射流J0及两板间距离的变化关系。虚阴极位置的数值结果与稳态理论给出的结果相近,它的振荡频率符合经验公式(1~√2π)ωpeb。单板时入射电子数密度按速度服从高斯分布,能散△En/En < 10%时的数值结果给出与单能情况基本相同的结论。 相似文献