退火对IrMn基磁隧道结多层膜热稳定性的影响

采用磁控溅射方法制备了结构为IrMn/CoFe/AlO_x/CoFe的磁性隧道结多层膜,样品置于真空磁场中进行退火处理. 将在不同温度退火的磁隧道结结构多层膜置于负饱和场中等待,研究退火温度对样品热稳定性的影响. 结果表明:退火提高了多层膜反铁磁层的单轴各向异性能,增加了样品的交换偏置;随着负饱和场等待时间的延长,被钉扎层的磁滞回线向正场偏移,交换偏置单调减小,但退火减弱了这种趋势. 关键词： 磁隧道结 交换偏置 磁化反转     

Ni/Pb(Zr,Ti)O3/TbFe2层状复合材料的谐振磁电特性研究

采用化学镀和黏接法制备层状磁电复合材料Ni/PZT/TbFe₂,研究其磁电性能及谐振频率随Ni层厚度的变化情况. 结果表明:Ni/PZT/TbFe₂层状磁电复合材料与其他结构的磁电性能不同,其一阶弯曲谐振峰值和纵向谐振峰值都很大. 随着Ni层厚度的增加,Ni/PZT/TbFe₂层状磁电复合材料的一阶纵向谐振峰值逐渐增大. 结合实验数据和理论计算值得出了材料的一阶弯曲谐振频率fr1和一阶纵向谐振频率f 关键词： 磁电效应 正磁致伸缩 负磁致伸缩 谐振频率     

退火时间对Fe80Si9B10Cu1非晶合金纳米尺度结构不均匀性和磁性能的影响

研究了经历不同时间退火后, Fe₈₀Si₉B₁₀Cu₁非晶合金结构弛豫过程中纳米尺度结构不均匀性的演变及其对合金磁性能的影响.基于小角X射线散射和原子力显微镜分析,随着弛豫的进行,合金的纳米尺度结构不均匀性逐渐衰减.结合穆斯堡尔谱分析结果,弛豫态合金综合软磁性能的提高可归因于纳米尺度结构不均匀性的减弱.从流变单元模型来看,随着弛豫程度的加深,流变单元的体积分数显著降低,部分流变单元湮灭并转化为理想弹性基体.一方面,弛豫态样品的原子结构排列更加紧密,磁交换相互作用更强,饱和磁感应强度也更高;另一方面,准位错偶极子的数量密度随着流变单元在弛豫过程中的湮灭而逐渐减小,磁畴壁的钉扎效应减弱,合金的磁各向异性下降,矫顽力降低.本文从结构不均匀性的角度研究了Fe₈₀Si₉B₁₀Cu₁非晶合金弛豫过程中磁性能变化的结构机制,有助于建立铁基非晶合金结构和磁性能之间的关联性.     

Study of structural and magnetic properties of Fe_(80)P-_9B_(11) amorphous alloy by ab initio molecular dynamic simulation

The structural and magnetic properties of Fe_(80)P_9B_(11) amorphous alloy are investigated through ab initio molecular dynamic simulation. The structure evolution of Fe_(80)P_9B_(11) amorphous alloy can be described in the framework of topological fluctuation theory, and the fluctuation of atomic hydrostatic stress gradually decreases upon cooling. The left sub peak of the second peak of Fe–B partial pair distribution functions(PDFs) becomes pronounced below the glass transition temperature, which may be the major reason why B promotes the glass formation ability significantly. The magnetization mainly originates from Fe 3d states, while small contribution results from metalloid elements P and B. This work may be helpful for developing Fe-based metallic glasses with both high saturation flux density and glass formation ability.     

Thermally activated magnetization reversal in magnetic tunnel junctions

In this paper, the magnetization reversal of the ferromagnetic layers in the IrMn/CoFe/AlO_x/CoFe magnetic tunnel junction has been investigated using bulk magnetometry. The films exhibit very complex magnetization processes and reversal mechanism. Thermal activation phenomena such as the training effect, the asymmetry of reversal, the loop broadening and the decrease of exchange field while holding the film at negative saturation have been observed on the hysteresis loops of the pinned ferromagnetic layer while not on those of the free ferromagnetic layer. The thermal activation phenomena observed can be explained by the model of two energy barrier distributions with different time constants.     

Influence of Ga+ ion irradiation on thermal relaxation of exchange bias field in exchange-coupled CoFe/IrMn bilayers

This paper reports that the CoFe/IrMn bilayers are deposited by magnetron sputtering on the surfaces of thermallyoxidized Si substrates.It investigates the thermal relaxations of both non-irradiated and Ga + ion irradiated CoFe/IrMn bilayers by means of holding the bilayers in a negative saturation field.The results show that exchange bias field decreases with the increase of holding time period for both non-irradiated and Ga + ion irradiated CoFe/IrMn bilayers.Exchange bias field is also found to be smaller upon irradiation at higher ion dose.This reduction of exchange bias field is attributed to the change of energy barrier induced by ion-radiation.     

Thermal Stability of CoFe/Cu/CoFe/IrMn Top Spin Valve

We present a study of thermal stability of the top spin valve with a structure of seed Ta （Snm）/Co75Fe25 （5 nm ） /Cu （2.5 nm） /Co75Fe25 （5 nm ） /Ir20Mn80（12 nm） /cap Ta （8 nm） deposited at room temperature by magnetron sputtering. A vibrating sample magnetometer fixed with a heater was used to record the magnetic hysteresis loops at variational temperatures and x-ray diffraction was performed to characterize the structure of the multilayer. The exchange field Hex and the coercivity of the pinned CoFe layer Hop decrease monotonically with increasing temperature. The coercivity of the free CoFe layer Hcf in the spin valve shows a maximum at 498K. The temperature dependences of Hex, Hop and Hcf have also been discussed.     

Thermal relaxation of exchange bias field in an exchange coupled CoFe/IrMn bilayer

This paper reports that a CoFe/IrMn bilayer was deposited by high vacuum magnetron sputtering on silicon wafer substrate; the thermal relaxation of the CoFe/IrMn bilayer is investigated by means of holding the film in a negative saturation field at various temperatures. The exchange bias decreases with increasing period of time while holding the film in a negative saturation field at a given temperature. Increasing the temperature accelerates the decrease of exchange field. The results can be explained by the quantitative model of the nucleation and growth of antiferromagnetic domains suggested by Xi H W et al. [2007 Phys. Rev. B 75 014434], and it is believed that two energy barriers exist in the investigated temperature range.     

Influence of Ga+ ion irradiation on the magnetisation reversal process and magnetoresistance in CoFe/Cu/CoFe/IrMn spin valves

Ga+ion irradiation is performed on the surfaces of IrMn-based spin valves and the effects of ion irradiation on the magnetisation reversal process and magnetoresistance(MR) are investigated.The results show that the exchange bias field and magnetoresistance ratio of the spin valve decrease with the increase of ion dose.The width of the forward step between the free layer and the pinned layer becomes gradually smaller with the increase of ion dose whilst the recoil step tends to be narrower with ion dose increasing up to 6×10 13 ions/cm 2 and the step disappears afterwards.Two peaks in the R-H curve are found to be asymmetric.     

局部塑性变形下铁基金属玻璃的致密化和非均匀性增强

本文研究了经局部塑性变形后, Fe₇₈Si₉B₁₃金属玻璃在原子尺度上的结构演变及其对合金显微硬度的影响.借助砂纸作为传力的媒介,充分放大了作用于带材表面上的等效压力,发生塑性变形后合金表面产生了大量的剪切带.基于倒空间和实空间的同步辐射X射线衍射分析,在塑性变形后,合金结构的致密度增大,过剩自由体积被排出,并由此揭示了Fe₇₈Si₉B₁₃金属玻璃在短程及中程尺度上原子协同重排行为.结合高分辨透射电子显微镜观察的结果, Fe₇₈Si₉B₁₃金属玻璃在发生塑性变形后,结构不均匀的程度将会加剧.此外,不同于单轴加载下金属玻璃的加工软化, Fe₇₈Si₉B₁₃金属玻璃在发生局部塑性变形后,维氏硬度增大,表现出局部的加工硬化行为.从自由体积的角度看,合金表面的大量剪切带可能是由于剪切带影响区域的重叠和交叉发生相互作用,并加速原子迁移,...