MnFeP0.45As0.55材料中的相变研究

利用不同的测量方法，研究了MnFeP_１-xAs_x（0.32关键词： MnFePAs 磁致伸缩 巡游电子变磁性 一级磁相变     

MnFeP_(0.45)As_(0.55)材料中的相变研究

利用不同的测量方法,研究了MnFeP1-xAsx(0·32相似文献   

MnFePo.45Aso.55材料中的相变研究

利用不同的测量方法,研究了MnFeP1-xAsx(0.32＜x＜0.66)材料巡游电子变磁性转变附近一级相变与其他物理性质变化的关系.可以发现,材料的一级相变是一个温度滞后为10K,但持续发生在至少66K的一个很大的温度区间的结构相变.磁性相变与一级相变的温度点并不对应.晶格突变与居里温度和一级相变温度点并不一一对应,属于磁致伸缩的机制,来源于磁弹性耦合.实验指出,顺磁-铁磁转变是在一级相变的过程中,由于晶格的连续变化,导致了a-b面内最近邻Fe-Fe原子间的距离增大,而非观察到的晶格突变所引起.     

一级相变磁制冷材料的基础问题探究

由于一级相变磁制冷材料发生磁相变时有晶胞体积的突变,相变过程中有相变潜热存在,其磁化过程中有许多磁学问题有待于进一步探究.本文以LaFe13-xSix合金为研究对象,在现有对磁一级相变基础问题的分析基础上,对一级相变材料中系统熵变、等温熵变、绝热温变、热滞、磁滞、铁磁与顺磁态两相共存的温度区间和磁场区间、制冷能力的计算等磁学基础问题进行了较为细致的探究.分析表明,在忽略完全铁磁态和顺磁态对磁热效应的贡献时,Maxwell方程和Clausius-Clapeyron方程计算熵变的值具有等效性.等温磁化过程中升温和降温曲线包围的面积SABCE(磁滞的大小),实际上是升温过程和降温过程中磁场做的净功,等于相变潜热之差.磁滞和热滞的大小与磁化过程数据测量的时间有关,测量时间越长则滞后越小,当相变是平衡相变则滞后为零.另外,对温度和磁场诱导磁相变过程进行了分析,提出了一级相变磁制冷材料制冷能力的不同计算模型.本文对一级相变磁制冷材料的磁学基础问题研究有一定的参考价值.     

热膨胀法原位观测SrCoO_(3-δ)材料的一级相变

在相变点处,若两相化学势的一阶导数不连续则为一级相变.材料发生一级相变时,必定伴随着体积的变化.用热膨胀方法原位观测了SrCoO_(3-δ)材料的一级相变过程.结果表明:SrCoO_(3-δ)材料在920℃时出现体积突变现象,对应六角相到立方相的转变.原位观测结果也进一步确认了多晶材料可通过测量其线膨胀来反映其体膨胀变化规律.     

Schlgl一级相变模型的核化问题

本文在提供Schlogl一级相变化学反应模型中在反映非平衡相变过程的波前(wavefront)波形和波速的基础上,提出用扰动匹配方法研究与该相变相联系的核化过程的临界核与临界泡内组分浓度分布和临界半径。     

Schl?gl一级相变模型的核化问题

本文在提供Schl?gl一级相变化学反应模型中在反映非平衡相变过程的波前(wave front)波形和波速的基础上,提出用扰动匹配方法研究与该相变相联系的核化过程的临界核与临界泡内组分浓度分布和临界半径。 关键词：     

SU(3)格点规范理论的解析研究

变分-累积量展开方法推广到研究SU(3)格点Wilson模型.对序参数元格能量计算到二级展开,四维时模型没有一级相变,与Monte Carlo结果一致.五维时有一级相变发生.方法可用于格点理论中与SU(3)群有关的各种问题的解析研究.     

存在双稳性的激光系统中的临界现象

通过实际事例研究了可能出现光学双稳性的激光系统中的临界现象，并且用平均场理论作详细描述，这里揭示了在作为远离平衡系统的上述激光器中一种更为特殊的临界点，它意味着一级相变与二级相变之间的转变。它十分类似于Ｌａｎｄａｕ（１９３７）在他著名二级（平衡）相变理论中所预见的“第二类相变（线）的临界点”。     

低密度Ar熔化及结晶的分子动力学模拟

采用有位移力的ＬｅｎｎａｒｄＪｏｎｅｓ（１２－６）势对微正则系综下低密度Ａｒ系统（简约数密度为ρ＝０．８５）的一级相变过程进行了细致的分子动力学模拟,发现Ａｒ系统的熔化过程是原子的崩塌过程,结晶过程和理想的完整晶体不同,是一活化过程：形核长大过程随温度的降低进行,原来均匀分布在系统中的自由体积呈集中分布,由此系统达到了更稳定的结晶状态。     

液Zn对Fe_2Al_5涂层侵蚀的相变过程研究

本文对Fe2Al5涂层在液态Zn中的侵蚀相变过程进行了研究,实验结果表明:在侵蚀初期,靠界面张力平衡的作用,先发生热侵蚀,在试样表面形成热蚀沟,当热蚀沟达到一定程度后,液Zn与Fe2Al5相由不浸润变为浸润;同时Zn原子扩散进入Fe2Al5相并形成Fe2Al5-Znx固溶体相(η相);随着侵蚀时间的增加,发生在腐蚀界面上的液Zn对Fe2Al5涂层的侵蚀过程是恒温相变过程,相变过程使Fe2Al5涂层发生定向熔化.相变的驱动力来自于相成分的改变所引起的各相自由能的变化及各相间的相平衡的重新建立.     

Minimum shear viscosity over entropy density at phase transition?—A counterexample

The ratio η/s, shear viscosity (η) to entropy density (s), reaches its local minimum at the (second order) phase transition temperature in a wide class of systems. It was suspected that this behavior might be universal. However, a counterexample is found in a system of two weakly self-interacting real scalar fields with one of them condensing at low temperatures while the other remains in the symmetric phase. There is no interaction between the two fields. In our mean field analysis the resulting η/s is monotonically decreasing in temperature despite the second order phase transition.     

Transition order and dynamics of a model with competing exchange and dipolar interactions

We performed Monte Carlo simulation of phase transitions from isotropic stripe phase with short-range order to long-range stripe phase in a model with competing ferromagnetic exchange and antiferromagnetic dipolar interactions on triangular lattice. We calculated phase diagram for different values of exchange and dipolar interaction constants ratio, η. We also determined the order of the transitions to stripe phases AFh of different stripe widths h: first-order phase transition was found to transitions into AF1 and AF2 phases, while transitions to AF3 and AF4 phases were of the second order. In the phase diagram the tricritical point was determined at the AF2 and AF3 phase boundary. We observed the peak of nematic phase at the transition region to the AF1 phase, but found it metastable at low values of η. We have also found that in AF1 phase spin relaxation corresponds to the Ising model dynamics. In phases AF3 and AF4 the dynamics slows down, and stripe domain growth with time is proportional to logt.     

LiIO3多型性相变的进一步研究

本文用差热分析、恒温热处理、X射线衍射等方法,对LiIO₃在常压的相变过程做了进一步的研究。对于LiIO₃的常压相变机制有了较为详尽的了解。并发现LiIO₃在高温可相对稳定存在三个相:β,η和δ,它们可分别自行熔化,其熔点相应为:432℃,421℃和416℃,从它们的热经历和存在的温度范围,表明其稳定性顺序为β>η>δ。在室温干燥空气中,与α相和β相共存的还有ζ相,ζ相升温放热转变为β相。在α相存在的温区里,ζ相经过长时间热处理并不转变为α相,同时,ζ相转变为β相的温度比α相高。与α→β的情况相同,β对ζ→β也有诱导作用。而且的ζ存在对α→β也有促进作用。θ相(θ₁与θ₂)与γ相一样,是相变过程的中间过渡相。 关键词：     

Short-time dynamics of the positional order of the two-dimensional hard disk system

We investigate the positional order of the two-dimensional hard disk model with short-time dynamics and equilibrium simulations. The melting density and the critical exponents z and η are determined. Our results rule out a phase transition as predicted by the Kosterlitz–Thouless–Halperin–Nelson–Young theory as well as a first-order transition.     

Chiral and UA(1) phase transitions in QCD: an analysis of the I=0 pseudoscalars

We study chiral and U_A(1) phase transition in the dilute gas approximation. A comprehensive analysis of the mass and mixing angel of η and η^′ reveals that in the transition of the quark-gluon-plasma droplets to the hadrons, besides the chiral phase transition, the U_A(1) phase transition also plays a significant and non-trivial role.     

Fluctuation study of pionisation in ultrarelativistic nucleus-nucleus interaction

The scaled factorial moments and the multifractal moments have been investigated in differentη-intervals to study the dynamical fluctuation of pions produced in 200 AGeV³²S-Ag/Br interaction. In order to investigate the detail characteristics of intermittency behaviour, theF-moments are extracted up to the eighth order of moments in differentM-intervals. The analysis indicates a non-thermal phase transition and different regime of particle production during the hadronisation process.     

An unusual structural phase transition in Rb2HfF6

An unusual structural phase transition in the crystalline compound Rb₂HfF₆ near room temperature has been observed from perturbed angular correlation (PAC) spectroscopy. Our measurements in this compound produce two different crystalline configurations characterized by ω_Q=74.1(1) Mrad/s, η~0, δ~0 and ω_Q=24.7(2) Mrad/s, η=0.53(1), and δ=4(2)%. From PAC measurements in different samples, it is found that crystal structure corresponding to ω_Q=74 Mrad/s, η~0 transforms to the other quite arbitrarily with temperature and no definite temperature corresponding to this transition has been observed. This can possibly be attributed to displacive phase transition.     

Phasenumwandlung zweiter Art als kritische Erscheinung eines inneren Phasengleichgewichtes

It is demonstrated that the transition in a state with two internal phases is a second order phase transition. The term internal phases means phase-like regions inside the system which are not separated by boundaries in the sense of ordinary phase boundaries, and the dimensions and shape of which as well as their properties as such are object of an equilibrium. In a generalization (quasi phases) a long ranged correlation of alternating or periodical character is considered as a typical element of the low temperature state. Such states can be described thermodynamically with the help of a new pair of variablesQ-η. The transition intoQ-η-T is generally analogous to the critical point of ordinary phase transitions inP-V-T, andη ～(?t)^1/3 andC _p～(?t)^?2/3 with a small constant of proportionality are obtained (t=T-T _u). Using the Pippard-relations in the formV-V _γ=(dT _γ/dP) (S-S _γ) the low temperature behaviour of the entropy and density surface as a function ofP andT near the transition line can be completely described. E.g. the saturation magnetization of a ferromagnetic model is derived proportional to (?t)^1/3. Under the action of a magnetic field the transition will be of first order when the saturation magnetization is achieved, without the outer field being analogous toP orQ. Should only one internal phase differ from the high temperature state we obtain an edge point (x=0 analogous to theμ ₁?x-diagram of solutions) with finite jump inC _p andη～({t). A possible relationship to the BCS- model of the supraconductors is indicated.     

ANALYTIC STUDY OF su(3) LATTICE GAUGE THEORY

The variational-cumulant expansion method has been extended to the case of lattice SU(3) Wilson model.The plaquette energy as an order parameter has calculated to the 2nd order expansion.No 1st order phase transition in the d=4 case is found which is in agreement with the monte Carlo results,and the 1st order phase transition in the d=5 case is clearly seen.The method can be used in the study of problems is LGT with SU(3) gauge group.