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1.
The magnetic susceptibility of Hg1–x Mn x Se1–y S y and Hg1–x Mn x Te1–y S y crystals is investigated by the Faraday method at H = 3 kOe in the temperature interval T = 77–300 K. It is established that the specific features of are due to Mn–S–Mn–S, Mn–Se–Mn–Se, and Mn–Te–Mn–Te clusters and mixed Mn–Se–Mn–S and Mn–Te–Mn–S clusters of different sizes in which the indirect exchange antiferromagnetic interaction between Mn atoms is realized through chalcogen atoms. Based on the dependences 1/Mn = f(T), the magnetic parameters are determined and their dependences on the crystal composition (x and y) are established.  相似文献   

2.
Results from percolation theory are used to study phase transitions in one-dimensional Ising andq-state Potts models with couplings of the asymptotic formJ x,y const/¦xy¦2. For translation-invariant systems with well-defined lim x x 2 J x =J + (possibly 0 or ) we establish: (1) There is no long-range order at inverse temperatures withJ +1. (2) IfJ +>q, then by sufficiently increasingJ 1 the spontaneous magnetizationM is made positive. (3) In models with 0<J +< the magnetization is discontinuous at the transition point (as originally predicted by Thouless), and obeysM( c )1/( c J +)1/2. (4) For Ising (q=2) models withJ +<, it is noted that the correlation function decays as xy()c()/|xy|2 whenever< c . Points 1–3 are deduced from previous percolation results by utilizing the Fortuin-Kasteleyn representation, which also yields other results of independent interest relating Potts models with different values ofq.  相似文献   

3.
For a one-dimensional array ofS N–1 spins (N 2) with isotropic pair interactions (and more general systems) with J(j–i) obeying supn[n–1 1 n j 2|J(j)|]<, we prove that every equilibrium state is invariant under the natural action ofSO(N). In particular, there is no long-range order of the conventional type. Included is the caseJ(n)=n –2.Research partially supported by U.S.N.S.F. Grant No. MCS-78-01885.S. Fairchild Scholar at Caltech. On leave from Departments of Mathematics and Physics, Princeton University, Princeton, New Jersey 08544.  相似文献   

4.
I give a proof of the Kosterlitz-Thouless transition for sufficiently anisotropic (J zJ x –1 =J zJ y –1 <2q (JKT)–J) two-dimensionalN-component rotators (N 3). The method is based on Wells' inequality and is related to mean field Gaussian inequalities.  相似文献   

5.
Ising and Heisenberg magnets with nearest-neighbor ferromagnetic exchangeJ 1 and next-nearest antiferromagnetic exchangeJ 2 and randomly distributed frozen-in nonmagnetic impurities of arbitrary concentration 1–x are studied by several methods: systematic series expansions inx, 1–x and inverse temperature (1/T) as well as Monte Carlo simulation. Depending onRJ 2/J 1,T andx the model is in paramagnetic, ferromagnetic, antiferromagnetic or spin glass phases. The microscopic magnetic structures of all these phases are investigated and found to be more complicated than usually (e.g., the ferromagnetic state contains spins and clusters either aligned antiparallel or not aligned at all, when frustration effects make bonds ineffective). We suggest that the concentrationx c of magnetic ions below which no (anti-)ferromagnetic long range order occurs depends onR continuously, andx c 1 at the multicritical point (R m ,T=0) where the order changes from ferromagnetic to antiferromagnetic. Our results for phase diagram, susceptibility etc. are compared to recent data on the Eu x Sr1–x S system and very good agreement is found.  相似文献   

6.
Angular Correlation of Annihilation Radiation (ACAR) is shown to be useful to examine the electronic structure of -phase Pd1–y Ag y H x system. Hydrogen absorption by Pd1–y Ag y alloys results in the increase of both nearly free andd-localized electron numbers in compliance with the KKR-CPA calculation outcomes. The investigation of -phase systems, PdH x hydrides as well as Pd1–y Ag y H x materials, failed because of a high concentration of lattice defects.  相似文献   

7.
This paper is devoted to the Schrödinger operatorP=–h 2 x y +V(x,y) onR x n ×R y p in the Born-Oppenheimer limith0. We study the case where resonances appear due to a well of the second electronic level, so that there can exist transition points only in the complex domain. We then prove that the widths of these resonances are exponentially small ash tends to zero.  相似文献   

8.
The electronic structure of (Cd x S y ) n clusters, wherex, y16 andn8, is calculated using the Extended Hückel method with charge and configuration selfconsistence. Variations of charge distribution, energy level structure, stability, etc. as the result of coupling of single Cd x S y , clusters with different intercluster distance are analysed. This coupling has a pronounced effect upon orbital energies and HOMO-LUMO difference at small intercluster distances. In contrast, atomic charges are close for double and single clusters. The coupling effects quickly fall down with intercluster distance.The work was performed under partial support of Fundamental Research Foundation of Belarus. The author thanks the referee for the valuable remark on a possible source of weak cluster-cluster interaction included in Discussion of the revised version.  相似文献   

9.
ZF, LF and TF SR experiments with antiferromagnetic (AF) ceramical samples La2–x Sr x CuO4–y have been performed in the temperature range 10–300 K. Zero field muon spin polarization functions obtained below the Neel temperature clearly show a nonzero initial precession phase-–0.35 rad. We propose an explanation based on existence of the dynamical magnetic fields on the muon.We thank Drs. A.G. Chistov and A.M. Brjazkalo from RSC Kurchatov Institute for the preparation the #2 La2CuO4–y sample.  相似文献   

10.
We consider an anharmonic crystal described by variablesS x ,x d ,S x , with one-body interaction ¦S x ¦ and nearest neighbor (n.n.) two body interaction ¦S x –S y ¦. We prove that, for d bounded, , where is the correlation function for the free boundary condition Gibbs state in ,>0 and are suitable constants independent of and . This generalizes previous results obtained in the case.Research partially supported by Consiglio Nazionale delle Ricerche.  相似文献   

11.
An influence of localized holes on magnetic properties of the CuO2 planes in quasi-2D antiferromagnets (La2CuO4, YBa2Cu3O+x etc.) is studied. It is demonstrated that the hole localized on the bond connecting Cu2+ ions gives birth to frustration which in a wide range of parameters behaves as the two-level system with the energyEJ, whereJ is the exchange interaction of the neighbouring copper spins. As a result forTE the spin-wave energy may noticeably decrease even at a low concentration of the holesc if the parametercJ|E| is not small. When this parameter is greater than unity, the reentrant transition may occur in the system. Experimental data presently available are in a qualitative agreement with the theoretical predictions.  相似文献   

12.
Shah  Prasanna  Gupta  Ajay  Sarma  D. D.  Kawaguchi  K. 《Hyperfine Interactions》2002,139(1-4):623-629
Temperature dependent Mössbauer measurements are done on the samples of La1–x Ca x Mn1–y 57Fe y O3 with x=0 and 0.25, and y=0.01. With decreasing temperature, the specimen with x=0.25 shows a paramagnetic to ferromagnetic transition around 175 K. In the specimen x=0.0, the temperature dependence of both the center shift () and the recoilless fraction (f) can be fitted very well with the Debye theory with a D=320±50 K. But for the specimens with x=0.25, f and show distinct deviations from the Debye behavior in the temperature range in which the resistivity shows a sharp decrease. Dips observed in both the f and around the transition temperature suggest that the Jahn–Teller distortion observed in these systems is dynamic in nature.  相似文献   

13.
We consider Ising spin glasses onZ d with couplingsJ xy =c y–x Z xy , where thec y 's are nonrandom real coefficients and theZ xy 's are independent, identically distributed random variables withE[Z xy ]=0 andE[Z xy 2 ]=1. We prove that if y |c y |= while y |c y |2=, then (with probability one) there are uncountably many (infinite volume) ground states , each of which has the following property: forany temperatureT<, there is a Gibbs state supported entirely on (infinite volume) spin configurations which differ from only atfinitely many sites. This and related results are examples of the bizarre effects that can occur in disordered systems with coupling-dependent boundary conditions.Research supported in part by NSF Grants DMS-9196086 and 9209053Research supported in part by U.S. Department of Energy Grant No. DE-FG03-93ER25155  相似文献   

14.
We study the long-time relaxation of magnetization in a disordered linear chain of Ising spins from an initially aligned state. The coupling constants are ferromagnetic and nearest-neighbor only, taking valuesJ 0 andJ 1 with probabilitiesp and 1–p, respectively. The time evolution of the system is governed by the Glauber master equation. It is shown that for large timest, the magnetizationM(t) varies as [exp(–0 t](t), where 0 is a function of the stronger bond strengthJ 0 only, and (t) decreases slower than an exponential. For very long times, we find that ln (t) varies as –t 1/3. For low enough temperatures, there is an intermediate time regime when ln (t) varies as –t 1/2. The results can be extended to more general probability distributions of ferromagnetic coupling constants, assuming thatM(t) can only increase if any bond in the chain is strengthened. If the coupling constants have a continuous distribution in which the probability density varies as a power law near some maximum valueJ 0, we find that ln (t) varies as –t 1/3(lnt)2/3 for large times.  相似文献   

15.
It is shown that the Yang-Mills measureZ h –1 e–S()/h[D], whereh>0, describing gauge fields on the two-sphere converges to a probability measure on the moduli space of Yang-Mills connections onS 2, ash0.This work was partially supported by NSF Grants DMS-8922941, and PHY-8912067  相似文献   

16.
Ga x In1–x As y P1–y alloys lattice matched to InP substrates are currently used to fabricate optoelectronic and integrated optics devices. To achieve devices with high performances and high fabrication yield, the uniformity and reproducibility of the Ga x In1–x As y P1–y epitaxial layers (composition, thickness, doping, etc.) have become key parameters. These problems have been addressed in the frame of ESPRIT project 2518 and are presented in this paper. Several aspects have been considered starting from the optimization of InP substrates, the MOVPE growth of uniform GalnAsP layers, the material characterization to the validation of material uniformity on passive optical waveguides. Both scanning photoluminescence analysis and waveguide losses measurements performed on 2 inch wafers with a high lateral resolution have shown that high quality uniform GalnAsP layers can be obtained reproducibly on 2 InP substrates using a commercially available LP-MOCVD growth process. In particular, more than 60% of 36 mm long, 3m wide and 100m spaced rib waveguides exhibit losses below 0.8dBcm–1.  相似文献   

17.
Accurate measurement of lattice parameters of Ag-Au solid solutions   总被引:3,自引:0,他引:3  
Using the ratio method in the variant effectiveD method the measurement of the lattice parameters of a solid solution of Ag-Au on samples of purity 99·999% was performed. The mean values of the parameters can be expressed by the functiony=4·086 17.x + 4·078 42. (1–x) –0·021 39.x(1–x) [Å] wherex is the atomic concentration of Ag. The mean displacement of the mean values of the parameters measured at single concentration is ±0·000 05 Å. A decrease of the lattice parameters of solid solutions to below the values of pure components was confirmed.The author thanks Assoc. Prof. M. Cernohorský CSc. for having introduced him to the problems of the precise measurement of lattice parameters and Mrs. V. Gregorová and L. Adamcová and Mr. M. Jelínek who took part in the experiments.  相似文献   

18.
The Transfermatrix-Method [1, 2] is applied to an Ising-spinglass-model on the square lattice with nearest neighbor interactionsJ 1 positive and next nearest neighbor interactionsJ 2 negative, when a fraction 1-x of the spins is removed at random. An example for this model is Eu x Sr1-x S [3, 4]. The question concerning the existence of a springlass-phase is not yet clarified. Investigation of the correlation function s 0sR2 (correlation between two spins with distanceR), which is related to the Edwards-Anderson-orderparameter shows in the present work evidence against a spinglass-phase at finiteT. Analogous to the more common ±J-model (competing nearest neighbor interactions at random) a phase transition should only occur atT=0.  相似文献   

19.
We show existence and uniqueness of asymptotically flat solutions to the stationary Einstein equations inS=3B r , whereB r is a ball of radiousr>0, when a small enough continuous complex function û on S is given. Regularity and decay estimates imply that these solutions are analytic in the interior ofS and also at infinity, when suitably conformally rescaled.  相似文献   

20.
The Cr3+ EPR spectra of YAG type crystals normally consist of four peaks whose positions are dependent on the axial zero-field splitting D with axis along a 111 direction and angle between that direction and the applied field H 0. In LLGG only three principal peaks are observed with zero-field axis nearly along x, y or z. This anomaly is attributed to the relatively small size of Cr3+ compared to Lu3+ which it displaces in an octahedral site. D varies slightly for the different zero-field axes: 0.480 cm–1 along x, 0.429 cm–1 along y and 0.470 cm–1 along z. The spectroscopic splitting factor g=1.978±0.001 is essentially isotropic and independent of axes within the experimental error.  相似文献   

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