哈斯勒合金Ni50Mn35In15的马氏体相变及其磁热效应

利用电弧炉熔炼了Ni50Mn35In15多晶样品,根据磁性测量对其马氏体相变和磁热效应进行了系统研究.结果表明.随着温度的降低,样品在室温附近先后发生了二级磁相变与一级结构相变特征的马氏体相变,导致它的磁化强度产生突变.同时通过低温下的磁滞回线的测量发现样品存在交换偏置行为,表明低温下马氏体相中铁磁和反铁磁共存.此外,根据Maxwell方程,计算了样品在马氏体相变温度附近的磁熵变,当温度为309 K,磁场改变5 T时,样品的磁熵变可达22.3 J/kg K.     

哈斯勒合金Ni50Mn35In15的马氏体相变及其磁热效应

利用电弧炉熔炼了Ni₅₀Mn₃₅In₁₅多晶样品,根据磁性测量对其马氏体相变和磁热效应进行了系统研究.结果表明,随着温度的降低,样品在室温附近先后发生了二级磁相变与一级结构相变特征的马氏体相变,导致它的磁化强度产生突变. 同时通过低温下的磁滞回线的测量发现样品存在交换偏置行为,表明低温下马氏体相中铁磁和反铁磁共存. 此外,根据Maxwell方程,计算了样品在马氏体相变温度附近的磁熵变,当温度为309K,磁场改变5 T时,样品的磁熵变可达22.3J/kgK. 关键词： 哈斯勒合金 50Mn₃₅In₁₅')" href="#">Ni₅₀Mn₃₅In₁₅ 马氏体相变 磁热效应     

Ni50.5Mn24.5G25单晶的预马氏体相变特性

通过交流磁化率、电阻、有无磁场下的预相变应变、磁致伸缩和磁化强度测量，系统研究了近正配分比Ni505Mn245Ga25单晶的预马氏体相变特性.在自由样品中观察到预马氏体相变应变.在预相变点，沿[010]方向施加大小约为80kA/m的磁场，在晶体母相的[001]方向上获得了高达505ppm的磁致伸缩，该值是相同条件下晶体母相磁致伸缩量的5倍多.同时，报道了不同方向磁场对预相变应变干预的结果.利用软模凝结的概念和依据单晶生长的特点，分析了预相变应变产生的机理.而磁场干预预相变应变的机理是磁场增大的磁弹耦合导致的晶格形变与材料内禀形变的竞争.利用磁性测量结果证实和解释了预相变过程中[001]和[010]轴方向间进一步增大的各向异性.进而对磁场沿[001]和[010]两个晶体学方向所导致的应变特性的差别，包括最大磁致伸缩、饱和预相变应变、饱和场等，进行了分析和讨论. 关键词： 预马氏体相变 应变 磁致伸缩 磁弹耦合     

Cu对Ni50Mn36In14相变和磁性的影响冰

文章研究了Cu替代部分Ni对铁磁性形状记忆合金Ni50Mn36In14相变和磁性的影响规律．研究表明,在Ni50-χcCuχMn36In14中,随着Cu含量的增加,相变温度逐渐降低．Cu含量低于5％时。奥氏体的磁性强于马氏体的磁性,母相和马氏体相的饱和磁化强度的差值△M随着Cu含量的增加而增大．当Cu含量χ=4．5时,△M迅速增加到80emu／g,并在该材料中观察到了磁场驱动的马氏体到奥氏体的转变,显示了该材料作为磁驱动磁电阻材料的潜在应用前景．当Cu含量高于5％时,奥氏体保持铁磁状态,马氏体相由反铁磁状态变为铁磁状态,马氏体的磁性强于奥氏体的磁性,△M大大削弱,磁场驱动性质消失．     

铁磁形状记忆合金Ni52.2Mn23.8Ga24的马氏体相变及其物理表征

对Ni52.2Mn23.8Ga24的单晶样品在马氏体相变过程中的相变潜热、磁性、电阻以及应变等物理序参量进行了测量.测量结果表明:不同的物理机制表征的相变温度有所不同.利用马氏体相变的GT关系予以分析,解释了不同测量方法获得的相变温度差别的原因.研究指出,Heusler合金Ni2MnGa的相变是分布晶格畸变类型,磁结构的变化发生在第二步晶格的非均匀切变,但相变应变与GT模型有区别. 关键词： 马氏体相变 Ni52.2Mn23.8Ga24     

铁磁形状记忆合金Ni52.5Mn23.5Ga24马氏体相变热滞后的研究

用相界面摩擦原理计算了Ni525Mn235Ga24单晶样品在马氏体相变过程中由于相界面摩擦所消耗的能量.计算结果表明,克服相界面摩擦所需要的能量为1314Jmol,仅占相变潜热的一小部分.另外,精细的交流磁化率测量样品的转变循环回线结果表明,相变热滞后的大小和马氏体的转变百分数成正比,从而进一步证明了热弹性马氏体相变的热滞后来源于相界面推移过程中的摩擦 关键词： 马氏体相变 Ni2MnGa     

Ni52Mn24Ga24单晶中取向内应力的热动力学计算

测量了Ni52Mn24Ga24单晶样品在磁场加载和未加载情况下马氏体相变时的相变应变.分析结果表明:用提拉法生长单晶时在晶体内部引入了单一取向的内应力,该取向内应力可诱导马氏体变体择优取向,从而导致马氏体相变时产生大的相变应变.从理论上计算了该内应力的大小.另外,对样品在马氏体态单纯磁诱导应变的热动力学研究,表明取向内应力在马氏体态依然存在.     

哈斯勒合金Ni-Mn-Sn的马氏体相变与反磁热性质

通过结构以及磁性测量,研究了哈斯勒合金Ni₅₀Mn_25+xSn_25-x (x=11,12)的马氏体相变和磁热性质.结果表明,与样品在奥氏体相的磁性不同,由于在马氏体相中反铁磁交换作用的增强,导致铁磁和反铁磁在马氏体状态下共存.此外,通过Maxwell方程,研究了两样品在不同磁场变化下马氏体相变温度附近的反磁热性质,并阐明了该系列合金产生大的正磁熵变(ΔS_M)不仅与其在降温过程中发生马氏体相变所导致的磁跃变(ΔM)有关,而且与发生马氏体相变所经历的温度区间有密切的联系. 关键词： 哈斯勒合金 Ni-Mn-Sn 马氏体相变 正磁熵变     

单晶Ni52Mn24Ga24中马氏体变体择优取向的物理表征

利用各种实验手段对M52Mn24Ga24单晶中马氏体变体的择优取向进行了表征.针对金相观察、磁场干预的相变应变、磁感生应变等实验结果,分析了马氏体相变过程变体自发择优取向和磁诱导择优取向的机理.根据不同方向磁场干预相变应变的结果,计算了Ni52Mn24Ga24单晶中等效取向内应力的大小约为2.45 MPa.从变体择优取向造成的有效弹性和磁畴分布两个方面,对单晶样品在[001]和[010]两个等价的晶体学方向上磁感生应变特性的差别,包括最大应变值、饱和场、滞后效应和起始磁场数值的参数,进行了分析和讨论.     

Ni52Mn24Ga24单晶中取向内应力的热动力学计算

测量了Ni₅₂Mn₂₄Ga₂₄单晶样品在磁场加载和未加载情 况下马氏体相变时的相变应变.分析结果表明：用提拉法生长单晶时在晶体内部引入了单一取向的内应力，该取向内应力可诱导马氏体变体择优取向，从而导致马氏体相变时产生大的相变应变.从理论上计算了该内应力的大小.另外，对样品在马氏体态单纯磁诱导应变的热动力学研究，表明取向内应力在马氏体态依然存在. 关键词： 马氏体相变 磁感生应变 内应力     

Optical spectroscopy of Ca3Sc2Si3O12, Ca3Y2Si3O12 and Ca3Lu2Si3O12 doped with Pr

The silicates Ca₃Sc₂Si₃O₁₂, Ca₃Y₂Si₃O₁₂ and Ca₃Lu₂Si₃O₁₂, both undoped and doped with Pr³⁺ ions, have been synthesized by solid-state reaction at high temperature. The luminescence spectroscopy and the excited state dynamics of the materials have been studied upon VUV and X-ray excitation using synchrotron radiation. All doped samples have shown efficient 5d-4f emission upon direct VUV excitation of 5d levels, but only Ca₃Sc₂Si₃O₁₂:Pr³⁺ shows luminescence upon interband VUV or X-ray excitation. The VUV excited emission spectra of Ca₃Y₂Si₃O₁₂:Pr³⁺ and Ca₃Lu₂Si₃O₁₂:Pr³⁺ show features attributed to emission from two distinct sites accommodating the Pr³⁺ dopant. The decay kinetics of the Pr³⁺ 5d-4f emission in Ca₃Sc₂Si₃O₁₂:Pr³⁺ upon VUV excitation across the band gap are characterized by decay times in the range 25-28 ns with no significant rise after the excitation pulse. They appear to be faster upon X-ray irradiation than for VUV excitation. Weak afterglow components are attributed to defect luminescence.     

Multilayer Bi1.5Zn1.0Nb1.5O7/Ba0.6Sr0.4TiO3/Bi1.5Zn1.0Nb1.5O7 thin films for tunable microwave applications

Bi_1.5Zn_1.0Nb_1.5O₇/Ba_0.6Sr_0.4TiO₃/Bi_1.5Zn_1.0Nb_1.5O₇ tunable multilayer thin film has been fabricated by pulsed laser ablation and characterized. Phase composition and microstructure of multilayer films were characterized by X-ray diffraction, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The film has very smooth surface with RMS roughness of 1.5-2 nm and grain size of 100-150 nm. Total film thickness has been measure to be 375 nm. The BZN thin films at 300 K, on Pt(1 1 1)/SiO₂/Si substrate showed zero-field dielectric constant of 105 and dielectric loss tangent of 0.002 at frequency of 0.1 MHz. Thin films annealed at 700 °C shows the dielectric tunability of 18% with biasing field 500 kV/cm at 0.1 MHz. The multilayer thin film shows nonferroelectric behavior at room temperature. The good physical and electrical properties of multilayer thin films make them promising candidate for tunable microwave device applications.     

La0.67Ca0.33MnO3薄膜皮秒光电效应

在1064 nm波长脉冲激光（脉宽25 ps）的照射下，钙钛矿氧化物薄膜La0.67Ca0.33MnO3/SrTiO3具有超快光电效应，对激光脉冲显示ps量级的响应时间，上升沿响应时间300 ps，半高宽700 ps，同时，对激光能量的响应灵敏度为500 mV/mJ。     

合成反铁磁Ni81Fe19/Co90Fe10/Ru/Co90Fe10/Ni81Fe19的研究

采用直流磁控溅射方法制备了一系列的合成反铁磁及以其为自由层的自旋阀.研究发现,在Ni₈₁Fe₁₉与Ru层之间插入适当厚度的Co₉₀Fe₁₀层后,可有效地提高合成反铁磁两磁性层间的反铁磁耦合强度,得到具有饱和场H_s更高、饱和磁化强度M_s更低、热稳定性更好的合成反铁磁.另外,以这种合成反铁磁作自旋阀的自由层时,可有效提高自旋阀的稳定性. 关键词： 合成反铁磁 退火 自旋阀     

Depolarization currents in the Na0.5Bi8.5Ti2Nb4O27 and Na0.5Bi8.5Ti2Ta4O27 layered ferroelectrics

The influence of the prehistory on the electrical properties of layered ferroelectrics is investigated. It is established that the heating of short-circuited samples of the nonpolarized ceramic material Na_0.5Bi_8.5Ti₂Nb₄O₂₇ leads to the appearance of maxima of the current at temperatures below the Curie point only in the case of preliminary ageing of the samples. Original Russian Text ? A.I. Burkhanov, Yu.V. Kochergin, K. Bormanis, A. Kalvane, M. Dambekalne, 2009, published in Fizika Tverdogo Tela, 2009, Vol. 51, No. 7, pp. 1393–1394.     

Structure and magnetic order in La0.7Ca0.3Mn0.5Co0.5O3 and La0.8Sr0.2Mn0.5Co0.5O3 perovskites

In this paper we report the study of the perovskites La_0.7Ca_0.3Mn_0.5Co_0.5O₃ and La_0.8Sr_0.2Mn_0.5Co_0.5O₃ by neutron powder diffraction at various temperatures and magnetization measurements in zero applied field and at low cooling regimes. The replacement of half Mn by Co in La_0.7Ca_0.3MnO₃ and La_0.8Sr_0.2MnO₃ destroys their long-range ferromagnetism exhibiting a cluster glass ferromagnetic order similar to the one observed in many cobaltites.     

Electrical transport and superconductivity in the Al2O3-Bi2Sr1.8Ca1.2Cu2Oy and MgO-Bi2Sr1.8Ca1.2Cu2Oy composites

We have measured the resistivities of Al₂O₃-Bi₂Sr_1.8Ca_1.2Cu₂O_y and MgO-Bi₂Sr_1.8Ca_1.2Cu₂O_y composites with the nominal Bi₂Sr_1.8Ca_1.2Cu₂O_y volume fraction, ₂₂₁₂, ranging from 0.15 to 1.00. For the Al₂O₃-Bi₂Sr_1.8Ca_1.2Cu ₂O_y composites, we find for the samples with ₂₂₁₂≥0.6 that the superconducting transition temperature, T_c, is not disturbed by the addition of Al₂O₃. For ₂₂₁₂<0.3, no zero-resistivity state is observed. For the MgO-Bi₂Sr_1.8Ca_1.2Cu₂O_y composites, T_c is barely disturbed for the samples with ρ₂₂₁₂≥0.7. No superconducting state is observed for the samples with ρ₂₂₁₂<0.35. The variation of (300 K) with ρ₂₂₁₂ indicates a three-dimensional percolating Bi-Sr-Ca-Cu-O matrix occurring at ρ₂₂₁₂≈0.19 and ≈0.15 in Al₂O₃-Bi₂Sr_1.8Ca_1.2 Cu₂O_y and MgO-Bi₂Sr_1.8Ca_1.2Cu₂O_y, respectively. Both resistivity and magnetization measurements suggest that the reactions of Bi₂Sr_1.8Ca_1.2Cu₂O_y with MgO are weaker than with Al₂O₃.     

Cross section determination for the reaction K+p → K+pπ+π−π0 and K+π+π+π−n at 8.2 and 16 GeV/c

The cross sections for the reactions: (a) K⁺p → K⁺pπ⁺π^?π⁺ and (b) K⁺p → K⁺π⁺π⁺π^?n have been determined at 8.2 and 16 GeV/c with the following results:at 8.2 GeV/c: (a) 0.99 ± 0.07 mb, (b) 0.41 ± 0.04 mb;at 16 GeV/c: (a) 0.72 ± 0.05 mb, (b) 0.28 ± 0.05 mb.Using the available data at other energies, the cross-section dependence of these reactions on the incident momentum is discussed.     

Appearance of an inhomogeneous superconducting state in La0.67Sr0.33MnO3-YBa2Cu3O7-La0.67Sr0.33MnO3 trilayers

An experimental study of proximity effect in La_0.67Sr_0.33MnO₃-YBa₂CU₃O₇-La_0.67Sr_0.33MnO₃ trilayers is reported. Transport measurements on these samples show clear oscillations in critical current (I _c) as the thickness of La_0.67Sr_0.33MnO₃ layers (d _F) is scanned from ∼50 ? to ∼ 1100 ?. In the light of existing theories of ferromagnet-superconductor (FM-SC) heterostructures, this observation suggests a long range proximity effect in the manganite, modulated by its weak exchange energy (∼2 meV). The observed modulation of the magnetic coupling between the ferromagnetic LSMO layers as a function of d _F, also suggests an oscillatory behavior of the SC order parameter near the FM-SC interface.      

An investigation of the processes e+e−→μ+μ−γ and e+e−→e+e−γ

The reactions e⁺e^?→μ⁺μ^?γ and e⁺e^?→e⁺e^?γ have been studied with the CELLO detector at the PETRA storage ring. Data have been collected from $\text{s}\text{=14}\text{GeV up to}\text{46.8}\text{GeV}$. In a Dalitz plot analysis of the data, good agreement is found with QED, except for the region Mx_μγe>0.8 where the probability that QED describes the high energy data is at the percent level.