电阻法间接测量居里温度

在磁性材料的实际应用中有时需要测量居里温度．采用电阻法测量在升温过程中电阻的变化从而来推算居里温度．结果表明．一般情况下．随着温度的升高电阻是增大的．当温度在居里点附近．电阻或者处于一稳定值或者有明显偏小现象．根据温度对电阻的影响可知居里点就在此范围内．     

大面积二维磁性材料的制备及居里温度调控

当前,尽管集成电路制造工艺水平不断提高,但受到量子效应的限制,器件尺寸的缩小使业界遇到了可靠性低、功耗大等瓶颈,微电子行业延续了近50年的"摩尔定律"将难以持续.2004年二维材料—石墨烯的问世,为突破集成电路的功耗瓶颈带来了新的机遇.由于低维特性,二维材料在一层或者几层原子厚度中表现出丰富多样的电学、磁学、力学和光学...     

由电感测量铁氧体材料的居里温度

为测量铁氧体磁芯材料的居里温度，将含有铁氧体磁芯的螺绕环置于自制的可变温度的样品室中，用电感测量仪测量螺绕环在不同温度下电感量．得到电感随温度的变化曲线，从而确定磁芯的居里温度．     

La(Fe,Si)_(13)化合物的居里温度机制

NaZn13型La(Fe,Si)13化合物随Si含量增加,相变性质由一级过渡为二级,化合物晶胞体积收缩,饱和磁化强度降低,居里温度升高.其居里温度与晶胞体积之间的关系不能用Bethe-Slater曲线给出合理的解释.本文利用添加间隙原子碳调节La(Fe,Si)13化合物晶胞体积和居里温度的方法,系统研究了该化合物居里温度与晶胞体积之间的关系.结果发现二者之间的变化规律遵循Jaccarino-Walker模型,即仅有5%甚至更少的3d电子被认为是真正的巡游电子,其余的3d电子仍是局域的.以极化的巡游电子为媒介,局域电子之间产生类似于Ruderman-Kittel-Kasuya-Yosida的长程相互作用,相互作用的符号和大小与距离呈周期性震荡.随Si含量的增加,La(Fe,Si)13化合物巡游电子数目增加,化合物的居里温度由晶胞体积和巡游电子的浓度共同决定.     

薄带非晶态磁性材料晶化温度的测量

利用普通电学测量方法，通过不同加热率和保温温度测量了非晶态磁性材料的电阻率随温度变化情况，找到了非晶体磁性材料的晶化温度及其变化规律．     

非晶态Co70Cr20Zr10合金在居里温度附近的磁性

本文研究非晶态Co₇₀Cr₂₀Zr₁₀合金在居里温度附近的磁性,样品的磁特性符合二级相变规律。得到临界指数β=0.45±0.02,γ=1.9±0.1,δ=5.13±0.05。Co₇₀Cr₂₀Zr₁₀合金的居里温度为T_c=(186.7±0.2)K。临界指数β,γ,δ满足γ=β(δ-1)关系,但临界指数值都偏离三维Heisenberg模型的理论值,这种行为可能起源于非晶态合金磁的不均匀性。讨论了Kouvel-Fisher(K-F)参数γ(T)对温度T的依赖关系。 关键词：     

交流电桥实验减小平衡指示的研究

通过对交流电桥接地机制的分析研究，提出一种有效降低干扰影响的改进电路，并通过对比给出了改进电路在平衡指零方面的实际效果。     

交流电桥实验的改进

本文对交流电桥实验中出现的问题,进行了一些研究,提出了用数字式万用表代替指零仪作检流计和改换接线方式的改进方法。     

交流电桥实验的计算机辅助分析

交流电桥实验的计算机辅助分析倪新蕾，潘元胜（南京大学物理系．２１０００８）交流电桥是测量交流元件的常用仪器，图１是测量电路，Ｚｘ为待测电抗元件的复阻抗，其平衡条件为：图１交流电桥众所周知，在交流电桥实验中，要使电桥完全调平衡是十分困难的，一般在平衡指...     

Chemical and structural disorder effects on the Curie temperature

The disorder effects on the Curie temperature of ferromagnetic and ferroelectric systems are studied by factorizing the spin–spin (or dipole–dipole) interaction into a chemical (on-site) and a structural (off-site) part. Assuming the statistical independence of the two contributions, the Curie temperature T_c is calculated in the limit of small disorder and in the mean-field approximation. The chemical disorder always enhances T_c . In the absence of spin waves (Ising-like systems), the structural disorder enhances T_c in turn. The only negative contribution to T_c is found in Heisenberg-like systems, and is ascribed to the interplay between structural disorder and spin waves. A comparison is made with other mean-field theories that adopt a different representation of the disorder. The application of the results obtained to real systems is considered, with special reference to recent experimental data on ferroelectric perovskites. An approximate expression, consistent with the mean-field approach, is suggested to estimate the relative weight of the chemical and structural disorder effects, even when an exact factorization is impossible, as is the case of the exchange interactions.     

Curie temperature and frustrated phase separation in manganites

There is an increasing experimental evidence that phase separation between insulating and metallic phase plays an important role in the physics of manganites. On general grounds one can argue that the electronic density in the metallic and insulating region will be generally different. This implies that phase separation of the ordinary “Maxwell construction” type is frustrated by the long-range Coulomb interaction. We present a generalization of Maxwell construction to this situation. The system is assumed to separate in islands of one phases hosted by the other. The size of the islands is determined minimizing a free energy that takes into account both surface energy and Coulomb effects. We discuss the peculiarities of this kind of phase separation and the consequences for the manganites. In particular, we present an explanation for the non-monotonous behavior of the Curie temperature as a function of doping.     

稀磁半导体材料居里温度的极值点

以Zener模型为基础,考虑反铁磁性交换作用对DMS材料居里温度的影响,理论计算得到了居里温度关于掺杂浓度和反铁磁性交换作用的二元函数,对GaAs ∶ TM(Ga,TM)As (TM=Sc,Ti,V,Cr,Mn,Fe,Co,Ni)的居里温度做了详细分析得到:n型半导体居里温度有一个极大值,而p型掺杂是单调的递增。     

Magnetic entropy change and magnetic properties of LaFe_(11.5)Si_(1.5) after controlling the Curie temperature by partial substitution of Mn and hydrogenation

Magnetic properties and magnetic entropy changes of La(Fe_(1-x)Mn_x)_(11.5)Si_(1.5)H_y compounds are investigated. Their Curie temperatures are adjusted to room temperature by partial Mn substitution for Fe and hydrogen absorption in 1-atm(1 atm = 1.01325×10~5Pa) hydrogen gas. Under a field change from 0 T to 2 T, the maximum magnetic entropy change for La(Fe_(0.99)Mn_(0.01))_(11.5)Si_(1.5)H_(1.61)is-11.5 J/kg. The suitable Curie temperature and large value of ?S_m make it an attractive potential candidate for the room temperature magnetic refrigeration application.     

Residual stress and Curie temperature of Fe-N thin films prepared by dc magnetron sputtering at elevated temperature

Fe-N thin films were prepared by dc magnetron sputtering at elevated temperature of 80 °C. The residual stress of the thin film was characterized by means of grazing incidence X-ray diffraction method. The effect of magnetron sputtering parameter on residual stress was investigated. The results indicate that the nitrogen content in working gas has great effects on the residual stress in the Fe-N thin film, and the residual stress increases firstly and then decreases with the increasing of nitrogen content in working gas. Curie temperature measurement shows that tensile residual stress enhances the ferromagnetic-paramagnetic transition temperature of Fe-N thin films under the condition of same phase composition.     

Dependence of the Curie temperature on the effective de Gennes factor in ferromagnets with exchange frustration

Considering the magneto-diluted gadolinium-containing Adamian alloys, it is shown that the dependence of the Curie temperature on the de Gennes factor ξ = c(g ? 1)2J(J + 1) can be expanded for ferromagnets with the exchange frustration. It is shown that in this case it is necessary to replace J by S _eff and that the linear dependence of T _C on ξ_eff remains up to the pure spin-glass state with S _eff = 0.     

The role of demagnetization factor in determining the ‘true’ value of the Curie temperature

The Curie temperature, T_C, is the temperature above which a material loses its long-range ferromagnetic order. Considering the equation of state of a ferromagnet in the mean-field approximation it has been shown theoretically that the value of the demagnetization factor N has a significant influence on the perceived location of T_C on the temperature scale. A series of precise measurements of magnetization using two differently shaped single crystals of high-purity gadolinium was carried out to prove this result experimentally and develop a procedure leading to the ‘true’ value of T_C.     

Effects of disorder on the Curie temperature of GaMnN, GaCrN, InCrN, and InMnN diluted magnetic semiconductors

The critical Curie temperatures of ordered and disordered diluted magnetic semiconductors based on GaN, InN, CrN, and MnN compounds are investigated using the classical Heisenberg model within the mean field approximation. The equilibrium structural lattice parameters of all the structures investigated are obtained from first principles. We show that the Curie T_c temperatures of disordered GaN and InN doped with small concentrations of Mn and Cr depends, to a great extent, on the Mn and Cr concentrations. Our calculations on these systems show that a T_c above room-temperature can be observed in these systems and it is affected greatly by the degree of disorder of Mn and Cr randomly distributed on the Ga and In sites. In addition, the ferromagnetic stability in these diluted magnetic semiconductors is studied systematically. Our results indicate that 3d Mn and Cr impurity states in GaN and InN favor the ferromagnetic state rather than the spin-glass phase.