磁控溅射法制备铁磁形状记忆合金Ni—Mn—Ga薄膜的力学性能研究

Ni-Mn-Ga是一种磁致伸缩材料、它兼具形状记忆效应和磁致伸缩效应等多种功能特点,具有响应频率高,变相量大的优点.而PbZrTiO3(PZT)是一种压电陶瓷,具有力-电转换的功能,而且也具有较高的响应频率.为实现磁-力-电的快速转换,本文使用ECR磁控溅射方法在PZT压电陶瓷片上制备出了Ni-Mn-Ga薄膜.并研究了不同溅射功率和热处理条件对薄膜的组织形貌、成分、表面粗糙度及薄膜硬度的影响.SEM断面形貌显示Ni-Mn-Ga薄膜为柱状生长模式;AFM三维形貌显示Ni-Mn-Ga薄膜生长致密,表面粗糙度随着溅射功率的增大而增大;Ni-Mn-Ga薄膜的硬度和弹性模量随退火温度的升高而增大.     

铸态及快淬态Ni50Mn26Ga19Fe5合金的磁致应变

研究了铸态及快淬Ni50Mn26Ga19Fe5掺杂合金的磁致应变性能.结果表明,掺Fe的Ni-Mn-Ga合金也具有典型的热弹性马氏体相变过程和磁转变过程,但铸态合金的结构为7层调制型马氏体(7M),而快淬合金的结构为14层调制型马氏体(14M).铸态合金最大磁致应变可达0.1%,快淬薄带合金最大磁致应变只能达到0.0095%.Ni50Mn26Ga19Fe5铸态合金比快淬合金有更大的磁致应变,说明掺杂元素Fe在Ni-Mn-Ga合金中的作用较为复杂.     

预加压应力对Ni-Mn-Ga-RE(RE=Tb,Sm)合金磁感生应变的影响

研究了稀土元素Tb和Sm对Ni-Mn-Ga磁性形状记忆合金的马氏体相变及磁致应变的影响,并着重研究了预加压应力对合金磁致应变的影响作用.结果发现,微量的稀土元素Tb和Sm的掺入,降低了合金的马氏体相变温度和居里温度.在施加一定的预加压应力后,其磁致应变值有大幅提高,并且大预加压应力在较低磁场下不能使合金产生最大磁致应变,但能够使合金在高磁场作用下获得大磁致应变,所以施加适当的预加压应力是提高合金磁致应变的有效方法.     

溅射制备Ni-Mn-Ga磁性形状记忆合金薄膜的组织结构研究

采用磁控溅射法制备Ni-Mn-Ga磁性形状记忆合金薄膜,并将制备薄膜在不同的温度下进行真空热处理.研究了不同工艺条件下制备薄膜的结构、形貌和磁性.结果表明:采用磁控溅射在单晶Si基底上溅射Ni-Mn-Ga磁性形状记忆合金薄膜,主要为沿基底法线方向的柱状晶结构,随着热处理温度提高,薄膜晶化程度提高,沉积在Cu基底上的薄膜磁性优于沉积在Si基底上薄膜的磁性.     

新型磁驱动形状记忆合金研究进展

磁驱动形状记忆合金是一种新型功能材料,由于兼具大的输出应变和高响应频率等综合特性,成为智能材料领域的研究热点之一.本研究首先总结了Ni-Mn-Ga合金在相变和磁致应变性能方面的特点,然后着重介绍了Co-Ni-Ga和Ni-Fe-Ga两类新型磁驱动记忆合金在结构、相变、形状记忆效应、磁性能等方面的研究进展,并对其中存在的问题进行了讨论.     

真空热处理对TbDyFe薄膜结构和磁学性能的影响

采用磁控溅射制备TbDyFe非晶薄膜,系统研究了不同温度和时间真空热处理对薄膜结构与磁学性能的影响.当热处理温度高于450℃时,薄膜中有磁致伸缩的RFe2结晶相形成.热处理使Tb0.28Dy0.72Fe2薄膜的易磁化方向从垂直于膜面向平行于膜面转变,并显著提高膜面内饱和磁化强度.450℃真空热处理60min后Tb0.29Dy0.71Fe1.8薄膜饱和磁化强度较高、矫顽力低,更容易在低场下磁化,适于低场下作为磁致伸缩薄膜应用.     

热处理对Tb0.27Dy0.73Fe2巨磁致伸缩薄膜性能的影响

本文研究了热处理对Tb0.27Dy 0.73Fe2薄膜磁性及巨磁致伸缩性能的影响.XRD分析表明制备态的Tb0.27Dy 0.73Fe2薄膜为非晶态,并且在450℃退火仍然保持非晶态,制备态的Tb0.27 Dy0.73Fe2薄膜显示垂直磁各向异性,在退火后向平行磁各向异性变化.热处理提高了Tb0.27Dy0.73Fe2薄膜在低磁场下的磁致伸缩特性.     

热处理温度对TbFe2/Fe交换耦合磁致伸缩多层膜的影响

采用直流磁控溅射在20mm×5mm×240μm抛光单晶硅片上制备了TbFe2/Fe磁致伸缩多层膜,主要研究了热处理温度对TbFe2/Fe磁致伸缩多层膜磁致伸缩系数的影响.采用量热分析法(DSC)、XPS以及光杠杆测试法对TbFe2/Fe磁致伸缩多层膜的晶化曲线、成分随深度的变化以及磁致伸缩系数进行了分析与测试.结果表明TbFe2薄膜的起始晶化温度为327℃,晶化温度为372℃;TbFe2/Fe磁致伸缩多层膜的最佳热处理温度为327℃,在此热处理温度下热处理60min,外加磁场1.6×104A/m时,TbFe2/Fe磁致伸缩多层膜磁致伸缩系数可达1.56×10-4.采用XPS分析了一个周期的TbFe2/Fe成分随薄膜深度的变化,未经热处理的薄膜Fe层和TbFe2层之间界面清晰,两层之间有少量的扩散.经327℃热处理60min的薄膜Fe层和TbFe2层界面发生了互扩散,原子数之比也发生了改变.     

超磁致伸缩薄膜研究进展

综述了近几年国内外超磁致伸缩单层膜、多层膜的研究进展;介绍了超磁致伸缩薄膜的制备方法与性能表征;论述了TbDyFe单层薄膜的磁致伸缩和磁学性能以及其成分、应力、热处理、衬底温度等性能的影响因素;详述了超磁致伸缩多层膜组成和结构类型;讨论了热处理、磁场诱导和单层膜厚对多层膜在低场下磁致伸缩和磁学性能的影响,评述和展望了超磁致伸缩薄膜的国内外研发应用现状和发展趋势.     

热处理对Fe81Ga19合金组织结构与磁致伸缩性能的影响

采用电弧熔炼法制备了Fe81Ga19合金多晶样品,研究了不同热处理工艺对合金组织结构及磁致伸缩性能的影响.样品经过700℃、800℃和900℃保温后采用空冷、炉冷和淬火3种冷却方式.结果显示,经过不同热处理后样品的微观组织均为单相bcc结构,而磁致应变从34×10-8到94×10-6不等;当热处理温度为800℃时,淬火处理后可获得较好的磁致伸缩性能(88×10-6),而热处理温度较高(900℃)时,采用炉冷的方式可获得较好的磁致伸缩性能(94×10-6).推测热处理方式和晶体取向对Fe81Ga19合金磁致伸缩性能有较重要的影响.     

Substrate dependent structural and magnetic properties of pulsed laser deposited Fe3O4 thin films

Nanocrystalline iron oxide thin films have been deposited on various substrates such as quartz, MgO(100), and Si(100) by pulsed laser deposition technique using excimer KrF laser (248 nm). The orientations, crystallite size and lattice parameters were studied using X-ray diffraction. The XRD results show that the films deposited on MgO and Si substrates are highly oriented and show only (400) and (311) reflections respectively. On the other hand, the orientation of the films deposited on quarts substrate changed from (311) to (400) with an increase in the substrate temperature from 400 degrees C to 600 degrees C, indicating thereby that the film growth direction is highly affected with nature of substrate and substrate temperature. The surface morphology of the deposited films was studied using Atomic Force Microscopy (AFM) and spherical ball like regular features of nanometer size grains were obtained. The magnetic properties were studied by Superconducting Quantum Interference Device (SQUID) magnetometer in the magnetic field +/- 6 Tesla. The magnetic field dependent magnetization (M-H) curves of all the Fe3O4 thin films measured at 5 K and 300 K show the ferrimagnetic nature. The electrochemical sensing of dopamine studied for these films shows that the film deposited on MgO substrate can be used as a sensing electrode.     

单晶PMnN-PZT铁电薄膜制备与表征

利用磁控溅射方法,在MgO基底上沉积三元系铁电薄膜6%PMnN-94%PZT(6%Pb(Mn1/3,Nb2/3)O3-94%Pb(Zr0.45,Ti0.55)O3),采用淬火方法对薄膜进行后期热处理。分别运用面内和面外X射线衍射(XRD)技术分析薄膜长相及晶体结构,运用高分辨率扫描电镜(SEM)观察薄膜的晶粒表面及截面结构。实验结果表明,所沉积薄膜为单晶钙钛矿结构薄膜,薄膜结构优良。     

Ordered, self-organized cobalt nanodots in Co-diamond-like carbon thin films

A formation process for ordered, self-organized cobalt (Co) nanodots in diamond-like carbon (DLC) thin films deposited by magnetron sputtering in a plasma-assisted Ar/CH4 discharge is presented. episilon-Co dots -5 nm in diameter, separated by 1-2 nm DLC boundaries and arranged in hexagonal arrays were produced on Si substrates. The formation mechanism relies on a self-organization process which is based on surface energy minimization and local magnetic field interaction. The proposed plasma-assisted process presents a controlled and cost-effective bottom-up nanofabrication approach for the production of well-ordered magnetic nanodots based on self-organization.     

Thickness dependency of sol-gel derived ZnO thin films on gas sensing behaviors

ZnO thin films were fabricated by a sol-gel method using Zn(CH₃COO)₂·2H₂O as starting material in order to prepare an acetone gas sensor. A homogeneous and stable solution was prepared by dissolving the zinc acetate in a solution of ethanol and monoethanolamine. The sol-gel solution is coated on alumina substrates with various thicknesses by spin coating technique and heat treated to grow crystalline ZnO thin films. The effect of thickness on physical and electrical properties of as deposited ZnO thin films has been studied. The as deposited ZnO thin films were characterized by X-ray diffraction spectroscopy, field emission scanning electron microscopy and atomic force microscopy. The root mean square surface roughness factors increase with thickness of the films and found 3.9, 6.6, 9.0, and 11.28 nm for 80-, 220-, 450- and 620-nm-thin films respectively. The activation energies of the films are calculated from the resistance temperature characteristics. The sensitivities of the ZnO films towards the acetone gas were determined at an operating temperature of 200 °C. The sensitivity towards acetone vapor is strongly depending on surface morphology of the ZnO thin films.     

The Influence of Mechanical Stresses on the Magnetic Properties of NiFe2O4 and CoFe2O4 Films

We have studied the influence of mechanical stresses on the magnetic properties of nickel ferrite (NiFev) and cobalt ferrite (CoFe₂O₄) films deposited on sapphire substrates with a- and c-oriented step terrace nanostructures. It is established that compressive stresses favor enhancement of the coercive field in thin ferrite films in the strain direction. Films of magnetically soft nickel ferrite with a room-temperature coercive field of 32.5 mT were obtained.

     

Reduction of Coercivity of Fe-N Soft Magnetic Film by Heat Treatment

200 nm thick Fe-N magnetic thin films were deposited on glass substrates by RF sputtering. The as-deposited films havehigh saturation magnetization but their coercivity is also higher than what is needed Therefore it is very important to reducecoercivity.The samples were vacuum annealed at 250℃ under 12000 A/m magnetic field. When the N content was in therange of 5～7 at. pct, the thin films consisted of α'+α" after heat treatment and had excellent soft magnetic properties of4πM_s=2.4 T, H_C<80 A/m. However, the thickness of a recording head was 2 μm, and H_c increased as thickness increased.In order to reduce the H_c, the sputtering power was raised from 200 W to 1000 W to reduce the grain size. 2 μm Fe-N thin     

Structure and magnetic properties of hcp and fcc nanocrystalline thin Ni films and nanoparticles produced by radio frequency magnetron sputtering

We report on the growth of thin Ni films by radio frequency magnetron sputtering in Ar-plasma. The growth temperature was about 350 K and the films were deposited on various substrates such as glass, silicon, sapphire and alumina. The thickness of the thinnest films was estimated by the appearance of Kiessig fringes up to about 2theta = 8 degrees in the small-angle X-ray diffraction pattern, as expected for high-quality atomically-flat thin films. With the help of this, a quartz balance system was calibrated and used for measuring the thickness of thicker samples with an accuracy of better than 5%. Structural characterization via X-ray diffraction and high resolution transmission electron microscopy revealed an Ar-gas pressure window, where single phase hcp Ni films may be grown. The magnetic response of the Ni films was checked at room temperature via a newly established and fully automatic polar magneto-optic Kerr effect magnetometer. The hcp films show no magnetic response. Interestingly, the magnetic saturation field of fcc films deposited at low Ar pressure is comparable to the one of bulk Ni, while the one of fcc films deposited at high Ar pressures is decreased, revealing the presence of residual strain in the films. Finally, it is shown that it is possible to form films which contain magnetic Ni fcc nanoparticles in a non-magnetic hcp matrix, i.e., a system interesting for technological applications demanding a single Ni target for its production.     

[MoO_4~(2-)]对Co-Mo共沉积机制及薄膜磁性能影响

从柠檬酸盐存在的酸性环境中电沉积制备了Co-Mo磁性薄膜.实验中固定电沉积条件,以循环伏安法和恒电位暂态法作为研究镀液中电化学响应的主要手段,研究了镀液中[MoO42-]对Co-Mo诱导共沉积机制的影响.结果显示:在酸性环境中,柠檬酸盐首先与钼酸盐形成络合物HrMoO4Cit[5-r],再生成钼氧化物.钴在镀液中主要是以CoHCit存在,CoHCit和钼氧化物同时从镀液中减少,最终达到共沉积,这主要取决于镀液中各离子的自身特性.薄膜磁性测量的结果表明:Co-Mo薄膜的易磁化轴平行于膜面.在与该轴平行方向上随镀液中[MoO42-]的增加,薄膜矫顽力(Hc//)增大,饱和磁化强度(Ms//)减小.镀液中[MoO42-]较低时,得到致密、光亮的Co-Mo磁性薄膜.     

稀土Dy掺杂纳米SnO_2薄膜的结构与气敏特性

采用真空蒸发法在玻璃衬底上制备稀土Dy掺杂Sn薄膜,对薄膜进行合适的氧化、热处理后获得Dy掺杂SnO2薄膜.用X射线衍射、场发射扫描电子显微镜、静态配气法对薄膜性能进行测试,研究不同掺Dy含量和热处理条件对SnO2薄膜的影响.结果显示,制备的SnO2薄膜呈金红石结构为n型;在相同热处理条件下,Dy掺杂可明显缩短薄膜氧化、热处理的时间;适当掺入稀土Dy可明显改善SnO2薄膜的结构、气敏特性.掺Dy 3at%后可大大提高SnO2薄膜对丙酮气体的灵敏度.     

Preparation and characterization of YBa2Cu3O7−x samples for microwave applications

We prepared several samples of YBa₂Cu₃O_7?x thick films electrophoretically deposited on metallic substrates, thin films sputtered on dielectric substrates, and bulk pellets, and we tested their microwave properties. Various preparation techniques are described in detail and the importance of appropriate thermal treatment during the fabrication process is emphasized. Experimental results show that electrophoretically deposited thick films on silver substrates reached, after heat treatment, a surface resistance at 50 K of 4×10^?2 Ω comparable with the silver value, while the same measurement before sinterization gave a value of 0.5 Ω. Either bulk pellets or thin films gave worse results, though a lack of sensitivity in our experimental apparatus could have influenced our data. The problem of sensitivity in the characterization of microwave properties of small samples is discussed in the appendices.