共查询到20条相似文献,搜索用时 703 毫秒
1.
The magnetic properties of a ferromagnetic thin film of face centered cubic (FCC) lattice with Heisenberg spin-S are examined using the high-temperature series expansions technique extrapolated with Padé approximations method. The critical reduced temperature of the system τc is studied as function of thickness of the film and the exchange interactions in the bulk, and within the surfaces Jb, Js and J⊥ respectively. A critical value of surface exchange interaction above which surface magnetism appears is obtained. The dependence of the reduced critical temperature on the film thickness L has been investigated. 相似文献
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Monte Carlo Simulation (MCS) has been used to study critical and compensation behavior of a ferrimagnetic superlattice on a simple cubic lattice. The superlattice consists of k unit cells, where the unit cell contains L layers of spin −1/2 A atoms, L layers of spin −1 B atoms and a disordered interface in between that is characterized by a random arrangement of A and B atoms of ApB1−p type and a negative A-B coupling. We investigate the finite and the infinite superlattices and we found that the existence and the number of the compensation points depend strongly on the thickness of the superlattice (number of unit cells). 相似文献
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Within the framework of the effective field theory, based on a probability distribution technique, we examine the critical and compensation behaviors of a ferrimagnetic alternating superlattice on a simple cubic structure. The superlattice consists of k unit cells each of which consists of L layers of spin-1/2 A atoms, L layers of spin-1 B atoms and a disordered interface with two layers in between that is characterized by a random arrangement of A and B atoms ApB1−pA1−pBp with a negative coupling A − B. Considering a finite and infinite superlattices, the effect of the thickness of the film and the surface exchange coupling on the magnetic properties are studied. The obtained results show a number of characteristic phenomena. 相似文献
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A. Saber G. Mattei X. Zhang 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(3):393-399
Within the framework of the effective field theory with a probability distribution technique that accounts for the single-site
spin correlations, we examine the critical behavior of the transverse ferromagnetic spin-1 Ising model of an alternating magnetic
superlattice. The critical temperature of the alternating magnetic superlattice has been studied as a function of the interlayer
and intralayer exchange interactions and the strength of the transverse field and the thickness of the finite superlattice.
Received 12 January 2000 and Received in final form 14 September 2000 相似文献
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Ilya Razdolski Ruslan R. Subkhangulov Diana G. Gheorghe Francis Bern Ionela Vrejoiu Alexey V. Kimel Andrei Kirilyuk Michael Ziese Theo Rasing 《固体物理学:研究快报》2015,9(10):583-588
Laser‐induced magnetisation dynamics of a La0.7Sr0.3MnO3/SrRuO3 superlattice is studied by means of a single‐colour optical pump‐probe technique. Significant differences in the magnetisation dynamics of a superlattice with respect to the single layers of constituent materials are demonstrated. Below the Curie temperature TC of SrRuO3, laser‐induced ultrafast demagnetisation is found to be followed by a uniform precession of the magnetisation around its new equilibrium. The data is described within a simple model based on a displacive excitation of a precessional magnetisation dynamics. The model is shown to give a good fit to the experimental data. As the initial temperature approaches TC, the oscillations get suppressed and eventually vanish. The magnetisation dynamics is shown to depend on whether the two distinct magnetisation vectors in the superlattice are ferromagnetically or antiferromagnetically aligned. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
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We have made a detailed study of the Si(111) 7 × 7 to “1 × 1” transition at 1140 K using low-energy electron diffraction. Excess diffuse scattering appears during the transition whose temperature dependence and magnitude are consistent with the loss of the 7th order superlattice intensities showing the transition is to a disordered surface phase rather than a true unreconstructed ×1. This strongly favors the class of models for the 7 × 7 selvedge involving an ordered arrangement of subunits like vacancies or adatoms rather than models with periodic distortion. The superlattice intensity shows the transition is continuous and reversible at least for temperatures below 0.995 Tc. The critical exponent for the long-range order is β = 0.11 ± 0.015 similar to those for 2D Ising or Potts models. However, the system does not show the critical scattering properties expected for simple models. The relaxation time seems to diverge near Tc but only for negative temperature increments. 相似文献
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Multiferroic properties of short period perovskite type manganite superlattice ((R1MnO3)n/(R2MnO3)n (n=1,2,3)) are considered within the framework of classical Heisenberg model using Monte Carlo simulation. Our result revealed the interesting behaviors in Mn spins structure in superlattice. Apart from simple plane spin cycloid structure which is shown in all manganites including bulk, film, and superlattice here in low temperature, a non-coplanar spiral spin structure is exhibited in a certain temperature range when n equals 1, 2 or 3. Specific heat, spin-helicity vector, spin correlation function, spin-helicity correlation function, and spin configuration are calculated to confirm this non-coplanar spiral spin structure. These results are associated with the competition among exchange interaction, magnetic anisotropy, and Dzyaloshinskii-Moriya interaction. 相似文献
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We study an (l,n) finite superlattice, which consists of two alternative magnetic materials(components) of l and n atomic layers, respectively. Based on the Ising model, we examine the phase transition properties of the magnetic superlattice. By transfer matrix method we derive the equation for Curie temperature of the superlattice. Numerical results are obtained for the dependence of Curie temperature on the thickness and exchange constants of the superlattice. 相似文献
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Mobility tensor, limited by island-like interface disorder, in type-I superlattices, is studied within a simple model (Kronig-Penney and plane waves). Computed results are presented, for GaAs-Ga1?xAlxAs superlattices, versus variations of temperature, superlattice period and defect parameters such as localisation, width and thickness. This interface scattering process has a significant influence on near equilibrium transport at low temperature. 相似文献
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U. Köbler R. Mueller L. Smardz D. Maier K. Fischer B. Olefs W. Zinn 《Zeitschrift für Physik B Condensed Matter》1996,100(4):497-506
We have examined the biquadratic exchange interaction strengths in the Europium monochalcogenides EuO, EuS, EuSe and EuTe using magnetization data of the paramagnetic phase and elaborate the consequences this additional interaction mechanism has on the magnetic phase diagrams of EuSe and EuTe. It is shown that the cubic susceptibility χ3 obeys a Curie-Weiss law at suffciently high temperatures and that the associated Curie-Weiss temperature θ3 is a measure for the biquadratic interaction strength. For all these materials the biquadratic interaction is ferromagnetic (θ3 > 0). This leads to a conflicting situation in the case of EuTe for which θ1 < 0. We attribute the peculiar observation, that the MnO superstructure reflection intensities as observed with neutron scattering correspond only to 0.6 of that moment expected for perfect magnetic order, to the presence of biquadratic interactions. The critical field Bc follows a T2 law in the spin-wave regime (T < 0.8 K) for EuTe and EuSe but for these two materials with an antiferromagnetic ground state the cubic susceptibility χ3 diverges at a temperature T* which is 2.5 K and 1.2 K above the ordering temperature, respectively. In the temperature range Tc < T < T* the magnetization curves exhibit some weak but definite anomaly which might be interpreted as a field-induced transition into the ferromagnetic state. A new multicritical point has been identified along the critical field curve Bc of EuSe. 相似文献
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I. D. Luzyanin V. P. Khavronin V. A. Ryzhov I. I. Larionov A. V. Lazuta 《JETP Letters》2001,73(7):327-330
The behavior of the linear and nonlinear dynamic susceptibilities of a Nd0.77Ba0.23MnO3 single crystal is studied with the aim to verify whether sealing theory is applicable for describing the critical phenomena in manganites with cubic symmetry. The experimental results obtained for the exchange temperature region (4πχ?1) agree well with the theoretical predictions, whereas the appearance of magnetically ordered formations in the paramagnetic phase is presumably due to the orbital ordering. 相似文献
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We investigate the ferroelectric phase transition and domain formation in a periodic superlattice consisting of alternate ferroelectric (FE) and paraelectric (PE) layers of nanometric thickness. We find that the polarization domains formed in the different FE layers can interact with each other via the PE layers. By coupling the electrostatic equations with those obtained by minimizing the Ginzburg-Landau functional, we calculate the critical temperature of transition Tc as a function of the FE/PE superlattice wavelength Lambda and quantitatively explain the recent experimental observation of a thickness dependence of the ferroelectric transition temperature in KTaO3/KNbO3 strained-layer superlattices. 相似文献
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D. A. Maslov Yu. B. Kudasov 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2009,3(4):500-502
The model of the magnetic structure of Fe/V superlattices is discussed. The discrepancy in estimation of the critical temperature for the Fe2/V n /Fe3/V n superlattice obtained by neutron scattering and the magneto-optical Kerr effect is caused by inhomogeneity of the magnetization distribution in a finite superlattice. 相似文献
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The magnetic properties of a ferromagnet spin-S a disordered semi-infinite system with a face-centered cubic lattice are investigated using the high-temperature series expansions technique extrapolated with Padé approximants method for Heisenberg, XY and Ising models. The reduced critical temperature of the system is studied as function of the thickness of the film and the exchange interactions in the bulk, and within the surfaces Jb,Js and J⊥, respectively. It is found that τc increases with the exchange interactions of surface. The magnetic phase diagrams (τc versus the dilution x) and the percolation threshold are obtained. 相似文献
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A. Saber P. Mazzoldi G. De Marchi S. Lo Russo G. Mattei 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(2):235-241
We examine the critical behavior of a magnetic superlattice which made up of two magnetic materials, A and B. Using the effective field theory with a probability distribution technique that accounts for the single-site spin correlation,
we derive the analytical equation for the Curie temperature of the superlattice which alternates as ABAB...AB. The dependence of the Curie temperature on the interface coupling strength Jab and the layer number of the finite superlattice was calculated. The effects of the surface modification are also studied.
Received 2 March 2001 相似文献
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Based on Landau-Devonshire (LD)-type phenomenological
thermodynamic theory, the electric field dependence of the
dielectric properties of tetragonal single-domain barium strontium
titanate(Ba1-xSrxTiO3) films on cubic substrates is
theoretically investigated by taking into account the high order
terms of the polarization. At room temperature, the nonlinear
dielectric responses of epitaxial Ba0.6Sr0.4TiO3
films are provided by adjusting the film thickness and growth
temperature. The strong nonlinearity of relative dielectric
constant and pyroelectric coefficient are attained around critical
film thickness on MgO (69 nm) and LaAlO3 (132 nm) substrates or
critical growth temperature on MgO (337 °C) substrate with
respect to epitaxy-induced lattice misfit and thermal stresses
during deposition. This can be explained that small compressive
stresses are effective to support high nonlinearity of dielectric
constant and pyroelectric coefficient for
Ba0.6Sr0.4TiO3 films irrespective of whether they are
on compressive substrate or tensile substrate. It is also
predicted that a large tunability may be achieved by altering
processing conditions, such as the film thickness and growth
temperature for different substrates.
Our theoretical results are in good agreement with the experimental data reported in literature. 相似文献