交换偏置增强反铁磁FeMn薄膜稳定性研究

采用磁控溅射方法制备了基片/Ta/NiFe(Ⅰ)/FeMn(Ⅰ)/NiFe(Ⅰ)/FeMn(Ⅰ)/Ta系列样品。实验发现,如果只是NiFe/FeMn交换偏置双层膜,在FeMn厚度大于3.5nm时才产生交换偏置。由于与NiFe之间的交换作用,即使2nm厚的FeMn(Ⅰ)也可以对NiFe(Ⅰ)产生交换偏置。结果表明,可以通过铁磁/反铁磁的交换耦合作用来增强反铁磁FeMn的稳定性。     

膜厚对NiFe单层膜及NiFe/FeMn双层膜性能的影响对比研究

采用直流磁控溅射法在Si(111)基片上制备不同厚度的Ni Fe单层膜、NiFe/FeMn双层膜,结合原子力显微镜(AFM)、振动样品磁强计(VSM)及电子顺磁共振(EPR)波谱仪研究了纳米膜的微观形貌、表面粗糙度、静磁性能及微波磁性能。结果表明,相对于Ni Fe单层膜,反铁磁性覆盖层FeMn的引入,使Ni Fe/FeMn双层膜的共振场(Hres)下降,与自旋波共振相关的有效交换场得以提升,说明在一定的外加稳恒磁场下,利用铁磁/反铁磁(FM/AF)多层膜结构所产生的钉扎效应能够提高薄膜的共振频率。在20～70 nm的NiFe薄膜厚度范围内,单层膜的共振场为1289～1354Oe,而双层膜的共振场降至1089～1118 Oe。     

磁控溅射Fe/Bi_(0.8)La_(0.2)FeO_3薄膜的交换偏置特性

利用磁控溅射法在单晶Sr Ti O3(001)基片上外延生长多铁Bi0.8La0.2Fe O3(BLFO)薄膜,研究了Fe/BLFO双层膜平面内的交换偏置和矫顽力特性受单层Fe膜厚度的影响。研究表明,在所研究的温度范围内,BLFO薄膜具有纯钙钛矿结构的单向(001)特性,基片温度为680℃时沉积的薄膜具有优异的生长取向。随Fe层厚度的增加,薄膜的偏置场平缓增大,在Fe层厚度为10 nm时具有最大值32 Oe,继续增加Fe层厚度,其交换偏置场迅速减小,然而矫顽力随Fe层的增厚持续增大。交换偏置场随Fe层厚度的变化规律可能与磁畴结构的变化有关。     

CoO膜厚对磁控溅射Co/CoO薄膜结构和磁性能的影响

为了探究FM/AFM双层膜中的交换偏置现象,利用磁控溅射法制备Co/Co O薄膜,通过改变沉积时间获得了不同Co O层厚度的Co/Co O双层膜系。通过X射线衍射(XRD)、扫描电子显微镜(SEM)、交变梯度磁强计(AGM)、超导量子干涉仪(SQUID)分别对样品的物相结构、表面形貌及磁性能进行分析和表征。结果表明,AFM层厚度对表面形貌有一定的影响,但表面成分不随AFM层厚度的变化而变化。所有样品的XRD谱均出现Co O(002)衍射峰,说明薄膜为晶态。不同厚度的Co/Co O双层膜样品表现出不同的矫顽力和偏置场,低温下样品的磁滞回线表现出明显的交换偏置效应,并且磁偏移量随膜层厚度增加呈现逐渐增大的趋势。当Co O厚度为62.5nm时,偏置场最大可达到420k A/m。     

制备条件对Fe-Ta-N薄膜的结构和软磁性能的影响

应用射频磁控溅射法制备了Fe-Ta-N薄膜,系统地研究了制备工艺地Fe-Ta-N薄膜结构和软磁性能的影响,首先,制备了不同钽含量的薄膜,发现（Fe89.5Ta10.5）-N薄膜具有很好的软磁性能,氮分压P（N2）=5%时,矫顽力获得最小值,Hc=14A/m。此时,样品呈现纳米晶结构,晶粒尺寸D≤10∧-8m,并且,钽掺杂能抑制铁氮化合物的生成,使薄膜在高氮分压范围内具有高的饱和磁化强度,Ms=1242kA/m。其次,考察了热处理对（F89.5Ta10.5）-N薄膜结构和磁性能的影响,P(N2）=5%时,沉积态薄膜为非晶结构,矫顽力很大;在热处理过程中,薄膜逐渐晶化,400℃热处理后,晶化度达到40%,形成纳米晶结构,矫顽力迅速减小,最后,比较了不同溅射功率和总气压对（Fe89.5Ta10.5）-N薄膜结构和磁性能的影响,发现薄膜可在较大的溅射功率和总气压范围内保持优异的软磁性能,是非常适于工业生产的薄膜磁头材料。     

退火处理对(FeCo)/Cu多层膜巨磁电阻及电磁性能的影响

采用直流磁控溅射法制备Ta/[(Fe89.6Co10.4)0.76 nm/Cu1.2 nm]25多层膜,X射线衍射试验结果表明,退火处理提高了薄膜的结晶度,退火温度达到550℃时,薄膜中发生Fe Co和Cu的相分离;AFM测试表明增加Ta缓冲层后可有效地降低薄膜的粗糙度;巨磁电阻(GMR)效应测量结果表明,随着退火温度的升高,样品的巨磁电阻效应呈现出先增大后减小的趋势,在350℃达到最大值-1.95%;薄膜的磁性饱和场随着退火温度的升高而变大,矫顽力亦增加,并在450℃时达到3.614×104A/m。     

基片温度对Ni81Fe19薄膜结构和各向异性磁电阻的影响

利用磁控溅射方法制备了一系列Ta(x)/Ni81Fe19(100nm)/Ta(3nm)磁性薄膜。着重研究基片温度、缓冲层厚度对薄膜结构和各向异性磁电阻的影响。利用X射线衍射仪分析了薄膜结构、晶粒取向;用四探针法测量了薄膜的电阻率和各向异性磁电阻。结果表明,基片温度对薄膜的各向异性磁电阻及饱和场有显著影响,随着基片温度的升高,薄膜各向异性磁电阻随之增大,饱和场则相反。基片温度在400℃时制备的Ni81Fe19薄膜具有较大的各向异性磁电阻比和较低的磁化饱和场,薄膜最大各向异性磁电阻比为4.23%,最低磁化饱和场为739.67A/m;随着缓冲层厚度的增加,坡莫合金薄膜的AMR值先变大后减小,在x=5nm时达到最大值。     

基片温度对Fe-N化合物薄膜制备及磁性能的影响

用X射线衍射仪和振动样品磁强计研究了双离子束溅射法制备的Fe—N薄膜的相组成和磁性能。结果表明,基片温度对不同基片上制得的薄膜的结构和磁性能有显著影响。基片温度为250℃和300℃时,在(111)硅片基片上制得无晶粒择优取向的单—γ″—Fe4N相;基片温度为160℃时,可在玻璃基片上制得具有(100)面晶粒取向的单一γ′—Fe4N相薄膜。薄膜磁性测量表明,与无晶粒择优取向的γ′—Fe4N相比较,具有(100)面晶粒取向的γ′—Fe4N相的矫顽力较低,易达到磁饱和,但二者的饱和磁化强度基本一致。     

外场取向对铁磁/反铁磁双层膜交换偏置的影响

利用斯通纳-沃尔法斯(Stoner-Wohlfarth,SW)模型详细讨论了铁磁/反铁磁双层膜交换偏置对外场取向角的依赖关系.解析推导出转换场和矫顽力的表达式.用两种办法计算了交换偏置场(he)和磁滞回线的半宽度(HWHL),结果分别用(he)s、(HWHL)s和(he)c、(HWHL)c表示.计算表明,(he)s、(...     

NiFe/CoFe复合自由层自旋阀巨磁电阻效应研究

采用高真空磁控溅射技术制备出无缓冲层NiFe/CoFe/Cu/CoFe/IrMn/Cu结构的自旋阀磁电阻薄膜.采用标准四探针法对自旋阀磁电阻比进行了测试,并利用振动样品磁强计(VSM)测量了样品的磁滞回线.结果表明:采用复合自由层NiFe/CoFe结构有效地提高了巨磁电阻比,相对于单一自由层结构自旋阀,巨磁电阻(GMR...     

NiFe/Cu多层膜的结构与层间耦合效应

用直流磁控溅射方法在玻璃基片上制备了[Ni_(80)Fe_(20)/Cu]_(20)多层膜,其中采用了靶表磁场强度不同的靶腔沉积铜层,利用X射线衍射和振动样品磁强计对Cu(100nm)/[Ni_(80)Fe_(20)(0.9nm)/Cu(tCu)]_(20)两个系列样品的结构和磁性进行了表征。靶表磁场较弱时沉积的多层膜具有良好的层间耦合振荡行为,而靶表磁场较强时制备的多层膜没有出现反铁磁耦合。依据上述事实,我们推测靶表磁场强度的不同会影响Ni Fe/Cu界面扩散,进而对多层膜样品的磁性产生影响。用靶表磁场较弱的靶腔沉积中间层铜能够有效减小界面互溶程度,改善镍铁与铜的成层质量。而靶表磁场较强的靶腔溅射出的铜原子具有较高能量,在界面处扩散并与镍铁层互溶,破坏了层状结构。     

射频溅射法制备的CoFe_2O_4薄膜结构及磁性能

采用射频溅射法在Si(001)基片上制备了CoFe_2O_4 (CFO)薄膜,分别采用原子力显微镜(AFM)、X射线衍射仪(XRD)、振动样品磁强计(VSM)进行测试和分析.结果表明,随着退火温度的升高,晶粒逐渐增大,在600℃左右退火,晶粒长大受到抑制;M_s和H_c随退火温度的升高都是先增大后减小;薄膜晶粒大小和膜内晶格应力导致垂直膜面方向矫顽力大于平面方向矫顽力.在600℃退火,H_(c⊥)/H_(c∥)值达到了2.72,表明制备的CFO薄膜具有高度垂直各向异性.     

Effect of Poling on Photovoltaic Properties in Highly Oriented BiFeO3 Thin Films

We report enhancement of photovoltaic properties of highly oriented BiFeO₃ (BFO) thin films. The single phase rhombohedral R3c space group structure was confirmed by XRD and Raman spectra in the films grown on SrTiO₃ (111) substrates using RF magnetron sputtering. The films of BFO were characterized in planar geometry with top Pt electrodes having 200μm diameter, ～40nm thickness and at a regular spacing of ～150μm deposited by DC sputtering process. For photovoltaic studies the current voltage characteristic of as grown and poled samples were studied under the white light illumination having energy density of ～1kW/m². The as grown films showed open circuit voltage (Voc) of ～3.9V which increased up to ～17.8V on poling with 200V. This enhancement in Voc by poling was attributed to increase in net polarization due to alignment of domains in the direction of applied electric field and hence potential barriers between the domains.     

Studies on Laser Ablated SrBi 2 Ta 2 O 9 and Sr 0.8 Ca 0.2 Bi 2 Ta 2 O 9 Ferroelectric Thin Films

Ferroelectric thin films of SrBi 2 Ta 2 O 9 (SBT) and (Sr 0.8 Ca 0.2 )Bi 2 Ta 2 O 9 (SCBT) were grown on platinized silicon substrates by using pulsed laser deposition technique. The effect of annealing temperature on the structural and electrical properties of the films was studied. Films were grown at 200 mTorr oxygen pressure with a constant substrate temperature at 500°C and annealed at different temperatures ranging from 700-800 °C in an oxygen ambient. X-ray diffraction data showed that as-grown films were crystalline nature. Atomic force micrographs showed that the grain size and surface roughness increased with increase in annealing temperature. The SBT films annealed at 800 °C showed ferroelectric properties with remanent polarization of 9.1 w C/cm 2 and coercive field of nearly 72 kV/cm. Whereas the SCBT films showed maximum remanent polarization of 7.3 w C/cm 2 with higher coercive field of 86 kV/cm. The higher coercive field in case of SCBT is attributed to the higher electronegativity of partially substituted Ca at Sr site. The dielectric constant increased with increase in annealing temperature and was attributed to the higher grain size.     

Processing and characterization of LiNbO3 thin film for metal Ferroelectric Semiconductor field effect transistor (MFSFET) application

Abstract

LiNbO₃ thin films were deposited on P-Si(111) substrates. C-axis (006) oriented films were fabricated with RF magnetron sputtering and (012) oriented films were achieved by metal organic decomposition (MOD). High frequency C-V measurement showed a clockwise rotation hysteresis curve, which corresponded to the ferroelectric switching. A polarization vs. voltage hysteresis curve of a Metal-Ferroelectric-Semiconductor (MFS) capacitor was measured with a modified Sawyer-Tower circuit. Remnant polarization as high as 65μC/cm² was found from sputtering deposited sample.     

低温固相反应法制备NiFe2O4纳米粉体

采用低温固相反应法制备了NiFe2O4铁氧体纳米粉体.用X射线衍射、振动样品磁强计及穆斯堡尔谱仪对样品进行了分析与观测.结果表明,该方法可以方便地得到纯度较高、粒径在9~35 nm之间、粒度分布均匀的尖晶石结构的NiFe2O4粉体.随着焙烧温度的提高相结构趋于完整,晶粒尺寸增大.随着晶粒尺寸的增大,样品饱和磁化强度随之增大,向块体逼近;平均超精细场也随之增大,穆谱数据还显示了样品的超顺磁转变尺寸为9 nm左右.     

Preparation of SrBi 2 Ta 2 O 9 Ferroelectric Thin Films by RF Magnetron Sputtering

Ferroelectric SrBi 2 Ta 2 O 9 (SBT) thin films were deposited by RF magnetron sputtering on a Pt/Ti/SiO 2 /Si(100) structure. The deposition temperature of the film was varied from RT (room temperature) to 600C. It was found that the SBT films were crystallized at temperatures between 500C and 600C, which was much lower than the annealing temperature (700C to 800C) of the RT-deposited film. The maximum remnant polarization value (2Pr) of the SBT film was 15 w C/cm 2 , which was deposited at 575C.