Ni53.2Mn22.6Ga24.2单晶的两步热弹性马氏体相变及其应力应变特性

对具有两步完全热弹性的Ni_53.2Mn_22.6Ga_24.2单晶的物性采用多种测量手段进行了表征,特别研究了不同温度下的应力-应变特性.研究表明,热诱发的中间马氏体相变应变远大于马氏体相变应变.在较低的形变温度下,沿单晶母相［001］方向的压应力诱发的是两步马氏体相变,材料表现出赝弹性;在较高的形变温度下,只能观察到一步马氏体相变,材料展现出完全超弹性特性.此外,利用热力学理论分别计算了诱发马氏体相变和中间马氏体相变的临界应力与形变温度的关系,与实验测量得到的结果相符. 关键词： 马氏体相变 形状记忆效应 应变 超弹性     

内应力对Mn2NiGa铁磁形状记忆合金的结构、相变和磁性能的影响

通过施加压应力的方法,在铁磁形状记忆合金Mn₂NiGa中引入残留内应力,研究了内应力对 Mn₂NiGa材料的结构、相变和磁性能的影响.研究发现,加压过程使材料发生了塑性形变,在材料内部引入了大量的位错缺陷.卸载后保留的位错缺陷在材料中造成了残留的内应力,导致了马氏体相变温度大幅度提高, 使原本室温下的母相转变成了马氏体相.测量到导致样品转变成马氏体的阈值压应力为1.0 GPa.加压形成的马氏体中的残留内应力将矫顽力从低于50 Oe提高到350 Oe.残留内应力在730 K的热处理中由于位错缺陷的消失而得以消除,样品实现了马氏体逆相变.如此高的逆相变温度使得 Mn₂NiGa马氏体的居里温度测量成为可能,获得了530K的数值.     

Cu对Ni50Mn36In14相变和磁性的影响

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Ni_50-xCu_xMn₃₆In₁₄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ΔM随着Cu含量的增加而增大. 当Cu含量x=4.5时, ΔM迅速增加到80 emu/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, ΔM大大削弱,磁场驱动性质消失.     

应变作用下量子顺电材料EuTiO3的磁电性质

由于磁性和介电性质的强烈耦合, 量子顺电材料EuTiO₃材料的研究近来倍受人们的关注. 本文通过运用基于密度泛函理论的第一性原理计算研究了量子顺电(PE) 材料EuTiO₃的磁性和电子结构, 分析了应变对磁性和结构相变的作用, 从而探讨了该材料中可能的磁电耦合机理. 结果发现, 在无应变状态下, EuTiO₃处于顺电立方-G型反铁磁性态, 而对于c轴方向的无论张应变还是压应变, 当应变增加到一定程度时, 由于Ti 3d空轨道与周围O 2p 电子的杂化平衡被打破, EuTiO₃将相变到铁电( FE) 四方-铁磁结构, 显示了强烈的自旋-晶格耦合效应.     

Tm3+/Yb3 :LiYF4单晶的高效近红外量子剪裁及其在光伏电池中的应用

采用改进的坩埚下降法成功地生长了Tm/Yb共掺氟化钇锂单晶. 该单晶体具有每吸收一个蓝色光子并能发射出2个1000 nm近红外光子的下转换发光效应. 测定了样品的激发光谱、发射光谱和荧光衰减曲线. 在465 nm蓝光激发下观察到由Yb³⁺：²F_5/2→²F_7/2能级跃迁所致的960～1050 nm 波段的发射带,此发光带源于Tm³ 对Yb³ 离子的能量下转换过程. 应用Inokuti-Hirayama模型,研究了晶体的能量转换过程,结果表明Tm³ 向Yb³ 的能量传递是一个电偶极子相互作用机制过程. 当Tm³ 与Yb³ 离子的掺杂浓度为0.49mol%与5.99mol%时,单晶的量子剪裁效率达到最大值167.5%.     

Er3+及Er3+/Yb3+掺杂ZrO2-Al2O3的制备及发光性质

采用共沉淀法制备了纳米晶ZrO₂-Al₂O₃∶Er³⁺发光粉体.所制备的粉体室温下具有Er3+离子特征荧光发射,主发射在绿光,其中位于547 nm、560 nm的绿光最强,并得出稀土离子与基质之间有能量传递.对不同煅烧温度下的样品研究表明:因不同温度下所制得的样品晶相不同.研究了纳米晶ZrO2-Al2O3∶Er3+及ZrO₂-Al₂O₃∶Er³⁺/Yb³⁺的上转换发光,并分析了上转换的跃迁机制.发现ZrO₂-Al₂O₃∶Er³⁺的绿光为双光子过程,而ZrO₂-Al₂O₃∶Er³⁺、Yb³⁺的上转换光谱中,红光和绿光也为双光子过程,而极弱的蓝光为三光子过程.讨论了Er³⁺的浓度猝灭现象.最适宜掺杂浓度的原子分数为2%（Er³⁺/Zr⁴⁺）.     

脉冲激光沉积温度及氧压对Bi2Sr2Co2Oy热电薄膜晶体结构与电输运性能的影响

利用脉冲激光沉积技术在c-Al₂O₃单晶基片上制备了Bi₂Sr₂Co₂O_y热电薄膜并研究了沉积温度和氧压对薄膜晶体结构及电输运性能的影响.在最佳沉积条件下制备的单相、c轴取向的Bi₂Sr₂Co₂O_y薄膜的室温电阻率ρ和塞贝克系数S分别为2.9mΩ/cm和110μupV/K,其功率因子S²/ρ好于在单晶样品上得到的值.此外,该薄膜在低温下表现出较强的负磁阻效应,在2K,9T时达到了40%.     

Ce3+ 掺杂高密度氧化物玻璃的闪烁性能研究

用高温熔融法制备了以SiO₂-B₂O₃-Al₂O₃-Gd₂O₃为基质系统Ce³⁺掺杂的玻璃样品, 测试样品的密度、紫外——可见透射光谱、紫外激发光谱和主要的闪烁性能, 并且把一部分闪烁性能和PbWO晶体及BGO晶体做比较. 着重研究了不同Ce³⁺掺杂浓度与Gd³⁺ 离子的含量对玻璃样品闪烁性能的影响规律. 结果表明: 玻璃样品具有较大的密度; 样品的X射线激发发射光谱发射峰位置都在390 nm左右, 当Ce³⁺ 离子的掺杂浓度为1.0 mol%(摩尔分数)、Gd₂O₃含量为15 mol%时, 玻璃样品的发光峰强度达到BGO晶体发光强度的90%; 同样验证了Ce³⁺ 离子具有浓度猝灭效应; Gd³⁺可以敏化Ce³⁺离子发光, 但是Gd³⁺离子到达一定浓度时, 反而会产生猝灭效应, 降低了Ce³⁺ 离子的发光. Ce³⁺ 离子掺杂SiO₂-B₂O₃-Al₂O₃-Gd₂O₃系统的闪烁玻璃有望替代闪烁晶体广泛应用于高能物理中.     

退火对He注入及随后208Pb27+辐照的Al2O3单晶PL谱的影响

利用高能离子研究了110 keV 的He⁺注入Al₂O₃单晶及随后230 MeV的²⁰⁸Pb²⁷⁺辐照并在不同温度条件下退火样品的光致发光的特性. 从测试结果可以清楚地看到在375 nm，390 nm，413 nm 和450 nm 出现了强烈的发光峰. 经过600 K退火2 h后测试结果显示，390 nm发光峰增强剧烈，而别的发光峰显示不明显. 在900 K退火条件下，390 nm的发光峰开始减弱相反在510 nm出现了较强的发光峰，到1100 K退火完毕后390 nm的发光峰完全消失，而510 nm的发光峰相对增强. 从辐照样品的FTIR谱中看到，波数在460—510 cm^-1间的吸收是振动模式，经过离子辐照后，吸收带展宽，随着辐照量的增大，Al₂O₃振动吸收峰消失，说明Al₂O₃振动模式被完全破坏. 1000—1300 cm^-1之间为Al-O-Al桥氧的伸缩振动模式，辐照后吸收带向高波数方向移动. 退火后的FTIR谱变化不大.     

Mn4+掺杂对BiFeO3陶瓷微观结构和电学性能的影响研究

利用传统的固相反应法制备了BiFe_1-xMn_xO₃ (x= 0-0.20)陶瓷样品, 研究了不同Mn⁴⁺掺杂量对BiFeO₃陶瓷密度、物相结构、显微形貌、 介电性能和铁电性能的影响.实验结果表明:所制备的BiFe_1-xMn_xO₃ 陶瓷样品的钙钛矿主相均已形成,具有良好的晶体结构, 且在掺杂量x=0.05附近开始出现结构相变.随着Mn⁴⁺添加量的增加, 体系的相结构有从菱方钙钛矿向斜方转变的趋势,且样品电容率大幅度增大, 而介电损耗也略有增加;在测试频率为10⁴ Hz条件下, BiFe_0.85Mn_0.15O₃ (ε_r=1065)的 ε_r是纯BiFeO₃ (ε_r=50.6)的22倍; 掺杂后样品的铁电极化性能均有不同程度的提高,可能是由于Mn⁴⁺稳定性优于 Fe³⁺,高价位Mn⁴⁺进行B位替代改性BiFeO₃陶瓷, 能减少Bi³⁺挥发,抑制Fe³⁺价态波动,从而降低氧空位浓度,减小样品的电导和漏电流.     

Si掺杂的铁磁形状记忆合金Co50Ni21Ga29Six的物性研究

成功生长了Co₅₀Ni₂₁Ga₂₉:Si(x=1,2)单晶样品,对其磁性,马氏体相变及其相关性质进行了细致的测量.发现掺Si成分的单晶具有非常迅速的马氏体相变行为、2.5％的大相变应变、大于100 ppm的磁感生应变和4.5％的相变电阻.进一步研究指出,在CoNiGa合金中掺入适量Si元素,能够降低材料的马氏体相变温度,减小相变热滞后,提高材料的居里温度,并使得磁性原子的磁矩有所降低.尤其重要的是Si元素的添加能够增大材料马氏体的磁晶各向异性能,改善马氏体变体的迁移特性,从而获得更大的磁感生应变. 关键词： 铁磁形状记忆合金 Heusler合金 50Ni₂₁Ga₂₉Si_x')" href="#">Co₅₀Ni₂₁Ga₂₉Si_x     

Ni47Mn32Ga21多晶合金的磁熵变和磁感生应变

对定向凝固方法制备的Ni₄₇Mn₃₂Ga₂₁多晶合金,通过扫描电镜、金相、电子能谱等手段研究其组份和组织形貌,通过对合金磁化强度与温度关系、等温磁化曲线及磁感生应变曲线等的测量分析,研究了合金结构相变和磁相变过程中的磁熵变及不同压力下的磁感生应变. 研究结果表明:合金组份与设计组份基本一致,室温下合金大部分为马氏体相. 升温过程中合金的磁熵变在居里温度(365 K)附近有最大值,并有较大的磁熵变峰值半高宽,747 kA/m的磁场下该磁熵变最大值为-1.45 J/kg ·K,磁熵变峰值的半高宽为21 K. 合金在室温(298 K)下有较好的双向可恢复磁感生应变,480 kA/m磁场下,无压力时合金的磁感生应变值达到-670×10^-6,并趋饱和;而在与磁场方向平行的27.3 MPa外压力作用下合金的磁感生应变值增大到-1300×10^-6,且未饱和. 关键词： Ni-Mn-Ga 铁磁形状记忆合金 磁熵变 磁感生应变     

The influence of Al substitution on the phase transitions and magnetocaloric effect in Ni43Mn46Sn11−xAlx alloys

The effects of Al substitution on the phase transitions and magnetocaloric effect of Ni₄₃Mn₄₆Sn_11−xAl_x (x=0-2) ferromagnetic shape memory alloys were investigated by X-ray diffraction and magnetization measurements. With the increase of Al content, the cell volume decreases due to the smaller radius of Al, and the martensitic transformation temperature increases rapidly, while the Curie temperature of austenitic phase shows a small increase. A large positive and a negative magnetic entropy change were observed near the first-order martensitic transition and the second-order magnetic transition, respectively. The magnetic entropy changes, hysteresis behavior, and refrigerant capacity near the two transitions are compared.     

The effect of Si content on the martensitic transfor-mation temperature of Ni55.5e18Ga26.5-xSix alloys

This paper investigates the effects of substitution of Si for Ga on the martensitic transformation behaviours in Ni-Fe-Ga alloys by using optical metallographic microscope and differential scanning calorimetry (DSC) methods. The structure type of Ni_55.5Fe₁₈Ga_26.5-xSi_x alloys is determined by x-ray diffraction (XRD), and the XRD patterns show the microstructure of Ni-Fe-Ga-Si alloys transformed from body-centred tetragonal martensite (with Si content x = 0) to body-centred cubic austenite (with x = 2) at room temperature. The martensitic transformation temperatures of the Ni_55.5Fe₁₈Ga_26.5-xSi_x alloys decrease almost linearly with increasing Si content in the Si content range of x ≤ 3. Thermal treatment also plays an important role on martensitic transformation temperatures in the Ni-Fe-Ga-Si alloy. The valence electronic concentrations, size factor, L2₁ degree of order and strength of parent phase influence the martensitic transformation temperatures of the Ni-Fe-Ga-Si alloys. An understanding of the relationship between martensitic transformation temperatures and Si content will be significant for designing an appropriate Ni-Fe-Ga-Si alloy for a specific application at a given temperature.     

Effect of Sn doping on the martensitic and premartensitic transitions in Ni2MnGa

The effect of Sn doping at the Ga site of Ni₂MnGa is investigated through magnetic and magneto-transport measurements. Clear signatures of martensitic and premartensitic transitions are observed in the pure as well as in 5% Sn doped alloy. For 10% Sn doping, the martensitic transition vanishes, while the premartensitic transition remains visible at low temperature. All the samples are found to have a ferromagnetic ground state with saturation moment decreasing with increasing Sn concentration. The magnetocaloric effect near the martensitic transition in the pure and 5% Sn doped samples is found to be positive. However, the entropy change is found to decrease with increasing magnetic field, which is particularly prominent in the undoped sample. The samples also show negative magnetoresistance with anomalies at the martensitic and premartensitic transition points.     

Effects of electron correlation and spin-orbit coupling on the electronic and magnetic properties of TbCu3Mn4O12

Electronic and magnetic properties of the three magnetic-sublattice double perovskite TbCu₃Mn₄O₁₂ (TCMO) are investigated by performing first-principles density-functional theory calculations. Our electronic structure calculations show that TCMO is half-metallic and its half-metallicity can only be correctly described when the electron correlation on Tb³⁺ 4f⁸ electrons are considered. The energies of different magnetic configurations among the three magnetic sublattices are also calculated, revealing that the magnetic configuration with Mn and Cu spins in the antiparallel arrangement and with the Tb magnetic moments ferromagnetically/antiferromagnetically (FM/AFM) coupled to Cu/Mn spins (that is Tb^↓Cu₃^↓Mn₄^↑O₁₂) is the lowest energetic magnetic state, which is consistent with recent experimental results. The magnetic anisotropy is further calculated for the [1 1 1], [1 1 0], and [0 0 1] spin quantization directions. It is found that the [1 1 1]-direction is more stable than the [1 1 0]- and [0 0 1]-directions by 123 and 135 meV per formula unit, respectively, indicating a significant magnetic anisotropy. Our detailed projected partial density of states analysis finally shows that Cu and Mn are antiferromagnetically coupled by superexchange interaction and Tb is expected to interact FM with A-site Cu and AFM with B-site Mn sublattices by way of 4f-2p-3d.     

High-spin structure in 187Pt

High-spin states in ¹⁸⁷Pt were studied via the ¹⁷³Yb(¹⁸O, 4n) reaction. Rotational bands based on the νi_13/2, ν7/2⁻[503], νi² _13/2νj, ν3/2⁻[512] and ν1/2⁻[521] configurations were observed, and interpreted within the framework of the cranked shell model. The TRS calculations show that the νi_13/2 band has an appreciable negative γ deformation, and the negative-parity bands tend to have a near prolate shape with small positive γ values. Experimental values of B(M1)/B(E2) ratios have been extracted and compared with theoretical values from the semi-classical D?nau and Frauendof approach, strongly suggesting a low frequency πh_9/2 alignment in the ν7/2⁻[503] band. Supported by the National Natural Science Foundation of China (Grant Nos. 10475097 and 10505025) and the Chinese Academy of Sciences     

Magnetic and magnetocaloric properties of martensitic Ni2Mn1.4Sn0.6 Heusler alloy

The evolutions of magnetic properties at low temperatures and the influence of magnetic field on the temperature dependence of specific heat in martensitic Ni₂Mn_1.4Sn_0.6 Heusler alloy are studied. The frequency-dependent blocking temperature and considerable exchange bias below it are measured in the martensitic phase. From the analysis of the specific heat curves under magnetic field, a large inverse magnetocaloric effect manifested as the magnetic field induced rise of isothermal magnetic entropy and/or magnetic field induced adiabatic temperature decrease in the vicinity of the reverse magnetostructural transformation and a significant value of the conventional magnetocaloric effect at the Curie temperature are obtained. The Debye temperature and electronic coefficient equal to Θ_D=310±2 K and γ= 16.6±0.3 mJ/K²mol, respectively, do not depend on the magnetic field.     

The doping effects of BiFe1-xCoxO3 (x=0.0-0.8) in layered perovskite Bi4Ti3O12 ceramics

Bi5Fe1-xCoxTi3O15(x = 0.0, 0.2, 0.4, 0.5, 0.6, and 0.8) multiferroic ceramics are synthesized in two steps using the solid state reaction technique. X-ray diffraction patterns show that the samples have four-layer Aurivillius phases. At room temperature (RT), the samples each present a remarkable coexistence of ferromagnetism (FM) and ferroelectricity (FE). The remnant polarization (2P r ) reaches its greatest value of 14 μC/cm 2 at x = 0.6. Remnant magnetization (2M r ) first increases and then decreases, and the greatest 2M r is 7.8 menu/g when x = 0.5. The magnetic properties for x = 0.4 are similar to those for x = 0.6, indicating that the magnetic properties originate mainly from the coupling between Fe 3+ and Co 3+ ions, rather than from their own magnetic moments.     

Magnetic and magneto-transport investigations of Co37Ni34Al29 alloy

Ferromagnetic shape memory alloy with nominal composition Co₃₇Ni₃₄Al₂₉ is investigated by transport and magnetic measurements. The anomaly due to the martensitic transition is observed around 130-210 K. The thermal hysteresis, observed due to martensitic transition in the dc magnetization versus temperature data, gets suppressed at higher applied field. Below 50 K, magnetization varies with temperature perfectly as T^3/2, which signifies that spin wave excitations are largely responsible for thermal demagnetization. The sample shows small negative magneto-resistance, which varies non-monotonically with temperature showing largest value at around 200 K.