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.     

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。     

磁控溅射法制备IrMn顶钉扎自旋阀研究

通过高真空直流磁控溅射的方法,在玻璃和硅上淀积了结构为Ta/NiFe/CoFe/Cu/CoFe/IrMn/Ta的IrMn顶钉扎自旋阀薄膜。通过结构的改善和工艺条件的优化,自旋阀的磁电阻率达到9.12％,矫顽力为1.04×(10~3/4π)A/m。研究了Ta缓冲层厚度(小于6nm)对晶格结构和自旋阀性能的影响。结果表明,Ta为3nm时自旋阀磁电阻率最大,而矫顽力随着Ta厚度增大而减小。利用CoFe/Cu/CoFe SAF结构替换掉与IrMn相邻的CoFe被钉扎层,使交换偏置场从原来没有SAF的180×(10~3/4π)A/m上升到600×(10~3/4π)A/m左右,且交换偏置场随着SAF结构中两层CoFe的厚度差减小而增大。研究了RIE对自旋阀性能的影响,发现2min的RIE能使矫顽力减小33％,而磁电阻率几乎不受影响。     

CoFe/Cu/CoFe/IrMn自旋阀结构多层膜磁化反转过程的研究

通过高真空直流磁控溅射的方法制备了结构为//Ta(5nm)/Co75 Fe25(5nm)/Cu(2.5nm)/Co75Fe25(5nm)/Ir20 Mn80(12nm)/Ta(8nm)的顶钉扎自旋阀结构多层膜,研究了磁场循环次数、反向饱和场等待时间和磁场变化率对自旋阀结构多层膜磁化反转过程的影响.结果表明,磁场循环次数和反向饱和场等待时间对自由层的磁化反转过程没有影响,而在被钉扎层中出现了练习效应和时间效应;磁场变化率对被钉扎层和自由层的前、后支反转场的影响变化趋势相似,但反铁磁层对被钉扎层的反转有一定的影响.     

巨磁电阻隔离器中自旋阀材料及结构研究

为得到矫顽力和工作偏置点都合适的自旋阀结构,实验中采用NiFe/CoFe复合层作为自旋阀自由层并通过调节NiFe和CoFe的厚度来控制自旋阀的矫顽力和灵敏度,并通过调节自旋阀中金属隔离层的厚度来控制自旋阀工作偏置点的位置。结果表明得到合适的自旋阀结构。在此基础上,采用光刻剥离工艺,制作两组折线形自旋阀巨磁电阻条样品,其磁化方向分别沿电阻条的长轴和短轴。测试结果表明磁化方向沿电阻条长轴的样品,矫顽力大小和工作偏置点稳定,灵敏度在电阻条宽度很小时有所减小;磁化方向沿电阻条短轴的样品,矫顽力和灵敏度大小稳定,而工作偏置点的位置随着电阻条宽度的减小逐渐偏离自旋阀钉扎场的方向。     

磁场退火对La_(0.7)Sr_(0.3)MnO_3低场磁电阻增强效应的研究

为了提高La0.7Sr0.3MnO3的低场磁电阻效应,将样品进行了磁场退火处理。实验结果表明,磁场退火并没有改变样品的磁矩,但对其磁各向异性产生了较大的影响。与零磁场下退火的样品相比,磁场退火样品的磁电阻明显提高。这种增强效应在低磁场下更加明显,在0.1 T的外磁场下,磁退火样品的磁电阻比零场退火的提高了140%。利用自旋极化隧穿机制解释了这种增强的磁电阻效应。     

CrPtMn顶钉扎自旋阀材料的交换耦合作用研究

反铁磁钉扎层和铁磁被钉扎层之间的交换耦合作用是高性能自旋阀材料研究中的一个关键因素。本工作研究了CrPtMn顶钉扎自旋阀材料中的交换耦合场(H_ex)与薄膜沉积条件以及退火处理之间的关系。研究表明: 沉积后的自旋阀材料中的H_ex大小与CrPtMn钉扎层的溅射工作气压关系不大, H_ex 约为7.96×10³ A/m。然而, 经过240℃退火2 h处理后, H_ex呈现出与CrPtMn沉积时的溅射工作气压相关的特性, 随着溅射工作气压的增加而增大。材料退火后的交换耦合场H_ex的温度特性良好, 室温下约为2.39×10⁴ A/m。Hex随着测试温度的升高而逐渐减小, 交换耦合场消失时的失效温度(blocking temperature)为315℃。     

NiFe／Co／Cu／Co结构自旋阀GMR效应及Co夹层的影响研究

用射频磁控溅射发射法成功制备了ＮｉＦｅ／Ｃｕ／Ｃｏ自旋阀多层膜材料,改变Ｃｕ层的厚度,研究材料的ＧＭＲ效应与Ｃｕ层厚度的关系,结果表明Ｃｕ为２．５ｎｍ时样品的ＭＲ值最大,其磁电阻效应ＭＲ可达１．６％,在ＮｉＦｅ和Ｃｕ之间插入一Ｃｏ薄夹层,通过对不同温度厚度Ｃｏ夹层的样品的ＭＲ曲线及磁滞回线的研究,讨论了Ｃｏ夹层对样品磁电阻的影响并分析了原因,结果表明插入适当的Ｃｏ层将提高材料的磁电阻效应,可达２．     

RIE对巨磁电阻自旋阀磁性能的影响

对巨磁电阻自旋阀磁场传感器制作中的关键技术之一：自旋阀薄膜的反应离子刻蚀(RIE)工艺,进行了试验研究。自旋阀结构为：Ta(3．5nm)／Cu(0．7nm)／NiFe(4．5nm)／CoFe(1nm)／Cu(3nm)／CoFe(2nm)／Ru(0．7nm)／CoFe(2nm)／MnIr(8nm)／Ta(4nm),刻蚀气体为氢氯碳氟化合物(HCFC：Hydro—chloro—fluoro—carbon),气体流量为10．5seem,RF功率为180W,时间为27min。结果表明：RIE技术可以加工出理想的巨磁电阻自旋阀薄膜图形,且加工过程对自旋阀的磁性能影响不大,这些结果对于巨磁电阻自旋阀型集成磁传感器的批量制作具有积极意义。     

退火对CoFe/IrMn双层膜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)/Ir20Mn80(12nm)/Ta(8nm)的双层膜,通过X射线衍射(XRD)、原子力显微镜(AFM)和振动样品磁强计(VSM)研究了退火对双层膜的结构及磁性能的影响;并通过样品在反向饱和场下停留不同的时间,研究了退火对双层膜的磁稳定性的影响。结果表明,退火使得IrMn(111)织构减弱,表面/界面粗糙度增大,交换偏置场减小,矫顽力增加,退火降低了双层膜的磁稳定性。     

Spin Valve Effect of 2D‐Materials Based Magnetic Junctions

The magnetotransport properties of spin valve structure are highly influenced by the type of intervening layer inserted between the ferromagnetic electrodes. In this scenario, spin filtering effect at the interfaces plays a crucial role in determining the magnetoresistance (MR) of such magnetic structures, which can be enhanced by using a suitable intervening layer. Here, the authors investigate the spin filtering effect of the two‐dimensional layers such as hexagonal boron nitride (hBN), graphene (Gr), and Gr‐hBN hybrid system for modifying the magnetotransport characteristics of the vertical spin valve architectures (Ni/hBN/Ni, Ni/Gr/Ni, and Ni/Gr‐hBN/Ni). Compared to graphene, hBN incorporated magnetic junction reveals higher MR and spin polarizations (P) suggesting better spin filtering at the interfaces. The MR for hBN incorporated junction is calculated to be ≈0.83%, while that of graphene junction it is estimated to be ≈0.16%. Similar contrast is observed in the ‘P’ of ferromagnets (FMs) for the two junctions, that is, ≈6.4% for hBN based magnetic junction and ≈2.8% for graphene device. However, for Gr‐hBN device, the signal not only get inverts, but it also suggests efficient spin filtering mechanism at the FM interfaces. Their results can be useful to comprehend the origin of spin filtering and the choice of non‐magnetic spacer for magnetotransport characteristics.

     

稀土超磁致伸缩材料的磁场热处理研究

超磁致伸缩材料是一种先进的能量转换材料,在高新技术和国防军工领域具有重要的应用价值。在概述TbDyFe超磁致伸缩材料的特点及发展现状基础上,重点介绍了<110>取向材料的磁场热处理研究。在实验方面,采用区熔定向凝固技术制备了<110>取向TbDyFe多晶材料,在略高于居里点温度退火时施加磁场,不改变晶体学择优取向和凝固组织,但能调控初始磁畴分布状态,改变服役时的磁矩运动过程,从而改善材料磁致伸缩和力学性能。在模拟研究方面,建立了基于能量最低原理的磁畴旋转模型,模拟了磁热感生各向异性诱导的初始磁矩再取向过程,得到了形成单轴各向异性的临界值;模拟了感生各向异性强弱对磁致伸缩"Jump"效应的影响规律,探讨了磁场热处理对<110>取向晶体磁致伸缩的作用机理。     

Nanoscale Magnetic Characterization of Tunneling Magnetoresistance Spin Valve Head by Electron Holography

Nanostructured magnetic materials play an important role in increasing miniaturized devices. For the studies of their magnetic properties and behaviors, nanoscale imaging of magnetic field is indispensible. Here, using electron holography, the magnetization distribution of a TMR spin valve head of commercial design is investigated without and with a magnetic field applied. Characterized is the magnetic flux distribution in complex hetero‐nanostructures by averaging the phase images and separating their component magnetic vectors and electric potentials. The magnetic flux densities of the NiFe (shield and 5 nm‐free layers) and the CoPt (20 nm‐bias layer) are estimated to be 1.0 T and 0.9 T, respectively. The changes in the magnetization distribution of the shield, bias, and free layers are visualized in situ for an applied field of 14 kOe. This study demonstrates the promise of electron holography for characterizing the magnetic properties of hetero‐interfaces, nanostructures, and catalysts.     

Tunable Spin Characteristic Properties in Spin Valve Devices Based on Hybrid Organic–Inorganic Perovskites

The hybrid organic–inorganic perovskites (HOIPs) form a new class of semiconductors which show promising optoelectronic device applications. Remarkably, the optoelectronic properties of HOIP are tunable by changing the chemical components of their building blocks. Recently, the HOIP spintronic properties and their applications in spintronic devices have attracted substantial interest. Here the impact of the chemical component diversity in HOIPs on their spintronic properties is studied. Spin valve devices based on HOIPs with different organic cations and halogen atoms are fabricated. The spin diffusion length is obtained in the various HOIPs by measuring the giant magnetoresistance (GMR) response in spin valve devices with different perovskite interlayer thicknesses. In addition spin lifetime is also measured from the Hanle response. It is found that the spintronic properties of HOIPs are mainly determined by the halogen atoms, rather than the organic cations. The study provides a clear avenue for engineering spintronic devices based on HOIPs.     

张力退火感生各向异性对纳米晶合金磁性能的影响

对Fe_74.1Cu₁Nb₃Si₁₅B_6.9(%,原子分数)纳米晶合金进行连续张力退火,研究了张力退火感生各向异性对纳米晶合金磁性能的影响。结果表明,张力退火产生的感生各向异性常数(K_u)与退火张力(σ)满足线性关系。随着退火张力的增大合金在f =5 kHz和H=3 A/m测试点的有效磁导率(μ_e)先增大后减小,且随着磁场和频率的提高有效磁导率(μ_e)的衰减减小。退火张力为67 MPa时有效磁导率(μ_e)在磁场强度H为0~800 A/m和频率f为1 k~3 MHz范围内保持约800,表现出恒导磁特性。同时,合金的单位质量损耗(P_m)随着退火张力的增大而减小,当退火张力为67 MPa时损耗为68 W/kg (测试条件：B_m=300 mT,f =100 kHz),与无张力退火相比下降约67%。同时,通过磁光克尔效应观察到张力退火后合金内部形成垂直于张力方向的180°片形畴,随着退火张力的增大磁畴宽度减小且趋于一致,退火张力为67 MPa时片形畴的宽度约为85 μm。     

自旋阀多层膜磁化翻转场的调控和磁电阻特性

用磁控溅射方法制备Ta/CoFe/Fe/Au/Fe/IrMn/Ta和Ta/CoFe¹/Au/CoFe²/IrMn/Ta两种多层膜结构的自旋阀,并优化各功能层的溅射参数有效调控了磁化翻转场和磁电阻特性。根据TEM确定了样品多层膜的微观结构和膜厚,使用VSM和加磁场四探针法分别测量了样品的磁滞回线和磁电阻(MR)特性曲线。结果表明,样品中隔离层Au的厚度与MR值之间存在振荡衰减的关系;而钉扎层、自由层和被钉扎层的厚度直接影响各膜层的矫顽力和饱和磁化强度等磁学性能,进而改变MR值。各层厚度为6/6/3.8/6/9/6 nm的Ta/CoFe¹/Au/CoFe²/IrMn/Ta结构自旋阀,具有最佳的MR值。     

退火工艺对铁基非晶薄带磁感应效应的影响

研究了频率、磁场强度以及退火工艺对Fe73.5Cu1Nb3Si13.5B9非晶薄带磁感应效应变化幅度的影响.研究结果表明:磁感应效应变化幅度随着磁场强度的增大而增大,随着频率的升高呈现先增大后减小的趋势;与淬火态非晶薄带相比,退火可以提高磁感应效应变化幅度,且经300℃×1h退火后的磁感应效应变化幅度最大.     

Spin Electronics: From Concentrated to Diluted Magnetic Semiconductors and Beyond

This presentation will review physical properties, relevant to spintronics, of concentrated magnetic semiconductors. Examples from the open literature and current research utilizing thin film EuS will be used as illustrations. New research on potential spin injection materials and spin detection will also be described. This latter work, carried out at MARTECH, the Center for Materials Research and Technology, demonstrates that carriers from the half-metal CrO₂ may be injected across an insulator without loss of (100%) spin polarization. It also features the development of a Hall gradiometer capable of detecting as few as 10⁵ spins.     

Intrinsic Spin Relaxation Processes in Metallic Magnetic Multilayers

Spin relaxation processes in metallic magnetic nanostructures are reviewed. First a brief review of the phenomenology of magnetic damping is presented using the Landau Lifshitz Gilbert (LLG) equations of motion. It is shown that the Gilbert damping in bulk metallic layers is caused by the spin orbit interaction and itinerant character of 3d and 4s-p electrons. Spin dynamics in magnetic nanostructures acquires an additional nonlocal damping. This means that a part of the magnetic damping is not given by the local Gilbert damping but arises from the proximity to other layers. Spin pumping and spin sink concepts will be introduced and used to describe the interface nonlocal Gilbert damping in magnetic multilayers. The modified LLG equation of motion in magnetic multilayers will be introduced and tested against the ferromagnetic resonance (FMR) data around the accidental crossover of FMR fields. The spin pumping theory will be compared to the early theories introduced in the 1970s for the interpretation of transmission electron spin resonance (TESR) measurements across ferromagnet/normal metal sandwiches.