不同缓冲层对NiFe／FeMn双层膜交换耦合场的影响

采用磁控溅射方法制备了NiFe/FeMn双层膜，分别以Ta,Cu作为缓冲层，Ta作为保护层。实验发现，以Ta为缓冲层的NiFe/FeMn双层膜的交换耦合场比以Cu为缓冲层的NiFe/FeMn双层膜的交换耦合场大，而矫顽力却很小。本分别从织构、界面粗糙度、界面偏聚等几方面对其中的原因进行了分析。除不同缓冲层引起的织构、界面粗糙度不同对交换耦合场有影响外，不同缓冲层引起的界面偏聚对交换耦合场也有影响。     

织构和界面粗糙度对NiFe/FeMn双层膜交换偏置场的影响

采用磁控溅射方法制备NiFe/FeMn双层膜（分别以Ta、Cu作为缓冲层，Ta作为保护层）。实验发现，以Ta为缓冲层的NiFe/FeMn双层膜的交换偏置场比以Cu为缓冲层的NiFe/FeMn双层膜的交换偏置场大，而矫顽力却很小。我们从织构、界面粗糙度两方面对其中的原因进行了分析。以Ta为缓冲层的NiFe/FeMn双层膜有好的织构且NiFe/FeMn界面较平滑，这引起了较强的交换偏置场和较低的矫顽力。     

插层Bi对NiFe/FeMn双层膜交换偏置场的影响及其XPS分析

在Ta／Cu／NiFe／FeMn／Ta薄膜中,我们曾发现Cu在NiFe层的表面偏聚导致NiFe／FeMn薄膜的交换偏置场降低。为了抑制Cu的表面偏聚,我们在Ta／Cu／NiFe／FeMn／Ta薄膜中在Cu／NiFe界面沉积Bi插层。实验发现,沉积适当厚度的Bi插层可以将NiFe／FeMn双层膜的交换偏置场提高1倍。XPS分析表明,在Cu／NiFe界面沉积的插层Bi有效地抑制了Cu在NiFe表面的偏聚,提高了交换偏置场。     

Ta缓冲层厚度对FeMn/NiFe体系交换偏置的影响

用X射线衍射仪、原子力显微镜和磁强计研究了Ta缓冲层厚度变化时,Ta/FeMn/NiFe/Ta多层膜微观结构和磁性能的变化,分析了其微观结构和磁性能之间的关系。实验结果表明,随Ta缓冲层厚度增加,FeMn层织构、晶粒尺寸、位错密度、应变和界面粗糙度都发生明显变化,并且这些变化影响了多层膜的偏置场(Hex)和矫顽力(Hc)的大小。结合实验现象和交换偏置(EB)的物理本质,讨论了微观结构对交换偏置的影响机理。     

硬磁/反铁磁交换耦合对反铁磁FeMn稳定性影响研究

采用磁控溅射方法在SiO2基体上制备了FePt/FeMn/NiFe/Ta多层膜样品,通过FeMn/NiFe双层膜交换偏置的变化研究了硬磁FePt不同磁化状态对反铁磁层FeMn的影响。实验表明,磁化了的L10相FePt能使FeMn在较薄的情况下(4.5nm)对NiFe产生比较强的交换偏置;而未被磁化的FePt对FeMn/NiFe交换偏置影响并不明显。认为更薄的反铁磁层对另外的铁磁层产生交换偏置是由于硬磁与反铁磁的界面交换耦合作用能增强反铁磁的稳定性。     

Pt插层对NiFe/FeMn薄膜交换耦合的影响

采用磁控溅射方法制备了以Pt为缓冲层和保护层的NiFe/FeMn薄膜.在NiFe/FeMn界面插入Pt,发现交换偏置场(Hex)随着插层Pt厚度(tPt)的增加而减小.一个重要的现象是当Pt插层厚度为0.4nm时,在Het-tPt衰减曲线并非单纯指数下降,而是出现一个"凸起".通过对样品磁矩随Pt插层厚度的变化规律进行分析,发现随Pt插层厚度的增加,样品的磁矩先逐渐增大,然后又有所下降,并且稳定在某一值;表明在样品制备过程中,NiFe与FeMn之间的相互作用(如界面反应),使得在NiFe/FeMn界面存在磁死层,Pt的插入抑制了NiFe/FeMn界面磁死层的产生,有利于交换耦合;另一方面,Pt的插入隔离了NiFe和FeMn的直接接触,使得FeMn对NiFe的钉扎作用减弱,不利于交换耦合.两个方面的共同作用,使得当Pt插层为某一合适厚度时,Hex-tPt曲线出现"凸起".     

不同缓冲层和保护层对NiFe/PtMn双层膜磁性的影响

制备了以Ta和非磁性NiFeCr作为缓冲层和保护层的NiFe/PtMn双层膜,研究了它们的结构和物性,结果表明:用NiFeCr做缓冲层和保护层的NiFe/PtMn双层膜,其交换偏置场比以Ta为缓冲层和保护层的NiFe/PtMn的交换偏置场有了10%的提高;退火处理以后,以NiFeCr为缓冲层和保护层的样品的磁性层NiFe的磁矩降低要小于以Ta为缓冲层和保护层的样品的磁性层NiFe的磁矩降低.同时,XRD测量计算发现,以NiFeCr为缓冲层生长的NiFe/PtMn样品比Ta为缓冲层生长的NiFe/PtMn样品具有更好的织构,更大的平均晶粒尺寸,因而具有更好的热稳定性.NiFeCr比Ta更适合做基于Mn合金为反铁磁层的缓冲层和保护层.     

基于各向异性磁阻的开关芯片的制备及优化

采用射频磁控溅射法用Ta作为缓冲层,在集成电路晶元上制备NiFe薄膜,并研究分析了Ta缓冲层厚度以及Ta缓冲层溅射功率对NiFe磁阻薄膜性能的影响,通过测试结果可以得到,当溅射功率由小变大时,NiFe薄膜的磁阻值也由小变到大。当Ta层的厚度在5nm左右时,NiFe更容易形成(111)织构,这时其磁阻值也最大。利用优化后的工艺,在晶元上制备NiFe薄膜,测试结果显示出开关特性,其开关场分别在398和796A/m左右。     

Pt/(Pt/Co)n/FeMn/Pt多层膜中Pt插层对交换偏置场的影响

在具有垂直磁各向异性Pt／（Pt／Co）n／FeMn／Pt多层膜中的Co／FeMn界面插入极薄的Pt层时，其交换偏置场有明显提高。研究结果表明：由于在Co／FeMn界面存在界面反应，破坏了（Pt／Co）n多层膜中靠近FeMn层的Co层的垂直磁各向异性，导致垂直交换偏置场Hex减弱。当在（Pt/Co）n与FeMn界面之间插入Pt层时可以有效地阻止这一反应发生，从而提高了多层膜的垂直交换偏置场Hex。     

退火对IrMn基自旋阀结构和磁性能的影响

采用高真空直流磁控溅射的方法制备了结构为//Ta(5nm)/Co75Fe25(5nm)/Cu(2.5nm)/Co75Fe25(5nm)/ Ir20Mn80(12nm)/Ta(8nm)的顶钉扎自旋阀多层膜,通过X射线衍射(XRD)、原子力显微镜(AFM) 和振动样品磁强计(VSM)研究了退火对自旋阀的结构及磁性能的影响.结果表明:退火使得IrMn(111)织构减弱,表面/界面粗糙度在低温退火后增大,而较高温度退火后减小;退火后交换偏置场和被钉扎层矫顽力减小,而自由层矫顽力增加;退火后自旋阀多层膜交换偏置场随样品在反向饱和场下停留时间的增加而不发生变化.     

Effect of Cu surface segregation on properties of NiFe/FeMn bilayers

The films of NiFe/FeMn with Ta and Ta/Cu buffer layers were prepared by magnetron sputtering. Results show that the exchange bias field of NiFe/FeMn films with Ta/Cu buffer is lower than that of the films with Ta buffer. The crystalline texture, surface roughness and element distribution of these two sets of samples were examined, and there is no apparent difference for the texture and roughness. However, the segregation of Cu atoms on the surface of NiFe in the trilayer of Ta/Cu/NiFe has been observed by using the angle-resolved X-ray photoelectron spectroscopy. The decrease of the exchange bias field for NiFe/FeMn films with Ta/Cu buffer layers is mainly caused by the diffusion of Cu atoms through NiFe layer, which stayed at the interface of NiFe/FeMn film or even intruded into FeMn layer. The present results indicate that Cu segregation through NiFe layer should be suppressed in order to improve the exchange bias field in giant magnetoresistance spin valves with Cu spacer.     

Influence of metal spacer on the properties and microstructure of multilayer films and analyses

Ta/NiFe/nonmagnetic metal spacer/FeMn/Ta films were prepared by magnetron sputtering. The dependence of the exchange coupling field (H_ex) between the FeMn and NiFe layers on the thickness of a nonmagnetic metal spacer layers was investigated systematically. The results show that H_ex decreases rapidly with increasing thicknesses of the Bi and Ag spacer layers. It decreases gradually, however, with an increase in the thickness of the Cu spacer layer. We found empirically that H_ex corresponds to the lattice match between spacer layer atoms and NiFe layer atoms. However, the results of X-ray photoelectron spectroscopy show that when a small amount of Bi atoms are deposited on the NiFe/FeMn interface, they migrate to the FeMn layer surface and hardly influence H_ex.     

Broadband microwave absorption in [NiFe/FeMn]n exchange-coupled multilayer films

[NiFe/FeMn]_n exchange-coupled multilayer films have been fabricated on the silicon substrate by magnetron sputtering deposition. The static and dynamic magnetic properties of multilayer films have been investigated with varying numbers of layers. The results show that the linewidth and permeability of imaginary resonance peak are increased with increasing numbers of layers. For the NiFe/FeMn/NiFe sample, the resonance frequency shows a different shift with applying external magnetic field along the direction of easy and hard magnetization axis of the sample, respectively, indicating a different magnetic reversal process in two ferromagnetic layers. It proved that the increase of linewidth was originated from the different interface exchange coupling.     

Ion beam deposition and structural characterization of GMR spinvalves

NiO exchange-biased “bottom” spin valves of the type NiO/NiFe/Co/Cu/Co/NiFe and FeMn exchange-biased “top” spin valves of the type NiFe/Co/Cu/Co/NiFe/FeMn were deposited by ion-beam deposition (except the NiO layer). Their magnetic properties, magneto-transport, and microstructures are characterized and compared with corresponding GMR spin valves deposited by dc magnetron sputtering. High-resolution cross-sectional transmission electron microscopy and X-ray diffraction reveal microstructural differences between ion-beam-deposited and dc magnetron sputtered spin valves. In particular, film texture, surface morphology, GMR ratio, exchange bias, interlayer coupling strength, and coercivity vary widely, but property-structure-processing correlation can be identified. A GMR ratio of ~9.7% was obtained on random textured NiO exchange-biased bottom spin valves by ion-beam deposition     

磁控溅射法制备IrMn底钉扎自旋阀研究

采用高真空直流磁控溅射的方法,在玻璃衬底上制备了结构为Ta／buffer layer／IrMn／CoFe／Cu／CoFe／NiFe／Ta的IrMn底钉扎自旋阀。研究了NiFe和Cu作为缓冲层对自旋阀磁性能的影响,并对缓冲层厚度进行了参数优化,当缓冲层厚度为2nm时自旋阀各项性能达到最佳。研究了退火制度对底钉扎自旋阀性能的影响,得到了30000e强磁场下200℃保温1h为最佳处理条件。通过结构的改善和工艺的优化,得到的底钉扎自旋阀的磁电阻率8．51％,矫顽场为0．50e,交换偏置场超过8000e。最后对自旋阀的底钉扎和顶钉扎结构进行了比较。     

Asymmetry of Magnetization Reversal of Pinned Layer in NiFe/Cu/NiFe/IrMn Spin-Valve Structure

Two types of asymmetry in giant magnetoresistance (GMR) are observed which are not related to a training effect, but indicate different mechanisms of magnetization reversal of the pinned layer in spin-valve (SV) structures for ascending and descending field scans. GMR, exchange bias and coercivity in Si/Ta/NiFe/Cu/NiFe/IrMn/Ta SV-structures were investigated as functions of the thickness of the nonmagnetic spacer. The spacer thickness effects are discussed in correlation with layers microstructure and interfaces morphology variations.