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.     

Influence of temperature on thermal relaxation of exchange bias field in CoFe/Cu/CoFe/IrMn spin valve

A multilayered spin valve film with a structure of Ta(5 nm)/Co_(75)Fe_(25)(5 nm)/Cu(2.5 nm)/Co_(75)Fe_(25)(5 nm)/Ir_(20)Mn_(80)(12 nm)/Ta(8 nm) is prepared by the high-vacuum direct current(DC) magnetron sputtering. The effect of temperature on the spin valve structure and the magnetic properties are studied by x-ray diffraction(XRD), atomic force microscopy(AFM), and vibrating sample magnetometry. The effect of temperature on the exchange bias field thermomagnetic properties of multilayered spin valve is studied by the residence time of samples in a reverse saturation field. The results show that as the temperature increases, the Ir Mn(111) texture weakens, surface/interface roughness increases, and the exchange bias field decreases. Below 200℃, the exchange bias field decreases with the residence time increasing, and at the beginning of the negative saturation field, the exchange bias field Hex decreases first quickly and then slowly gradually. When the temperature is greater than 200℃, the exchange bias field is unchanged with the residence time increasing.     

Effects of Cu dilution in IrMn on the exchange bias of CoFe/IrMn bilayers

The effect of nonmagnetic dilution in metallic antiferromagnets (AFMs) on the exchange bias (EB) has been investigated from a structural, magnetic, and Monte Carlo simulation point of view in bilayers of CoFe/(IrMn)1-xCux. Dilution by Cu atoms throughout the volume of the AFM IrMn gives rise to an enhanced EB field (HEB) for 5 K相似文献   

PtMn层厚度对NiFe/PtMn双层膜交换偏置形成及热稳定性的影响

采用磁控溅射的方法制备了一组以(Ni_0.81Fe_0.19)_1-xCr_x作为缓冲层的NiFe/PtMn双层膜样品，研究了NiFe/PtMn双层膜的形成过程和热稳定性.实验表明，Cr成分的不同会引起NiFe/PtMn双层膜中PtMn层晶粒尺寸的不同，使NiFe/PtMn双层膜的交换偏置场与PtMn层厚度之间呈现不同的变化关系.热稳定性实验表明，PtMn晶粒尺寸较大的样品，出现交换偏置现象所需要的临界厚度较小，热稳定性好，这与Mauri的理论模型一致. 关键词： NiFe/PtMn双层膜 交换偏置场 热稳定性     

外应力场下铁磁/反铁磁双层膜系统中的交换偏置

采用自由能极小的方法研究了铁磁/反铁磁双层膜系统在外应力场下的交换各向异性.本模型中铁磁层具有单轴磁晶各向异性和立方磁晶各向异性，而反铁磁层仅具有单轴磁晶各向异性，但其厚度趋于半无穷.理论上解析地给出了系统的等效交换偏置和钉扎角(它显示了反铁磁层对铁磁层磁化的钉扎作用)与外应力场之间的关系.数值计算表明：系统的等效交换偏置与外磁场的方向有关，而与其大小无关；然而外应力场的大小和方向均对系统的等效交换偏置有影响，其根源在于外应力场的大小和方向都影响着钉扎角. 关键词： 铁磁/反铁磁双层膜 交换偏置 钉扎角 应力场     

The structure dependence of exchange bias in ferromagnetic/antiferromagnetic bilayers

The structure dependence of exchange bias in ferromagnetic/antiferromagnetic （FM/AF） bilayers has been investigated in detail by extending Slonczewski＇s ＇proximity magnetism＇ idea. Here three important parameters are discussed for FM/AF bilayers, i.e. interracial bilinear exchange coupling J1, interracial biquadratic （spin-flop） exchange coupling J2 and antiferromagnetic layer thickness tAF. The results show that both the occurrence and the variety of the exchange bias strongly depend on the above parameters. More importantly, the small spin-flop exchange coupling may result in an exchange bias without the interracial bilinear exchange coupling. However, in general, the spin-flop exchange coupling cannot result in the exchange bias. The corresponding critical parameters in which the exchange bias will occur or approach saturation are also presented.     

铁磁/反铁磁双层膜中冷却场对交换偏置场的影响

用铁磁畴壁模型研究了非补偿界面铁磁/反铁磁双层膜中冷却场（包括大小及其方向）对交换偏置场h_E的影响.结果表明：当冷却场的方向与反铁磁层磁易轴一致时,h_E大小与冷却场大小无关.当冷却场的方向偏离磁易轴时,h_E的大小随偏离角度的增大有缓慢的改变,但当冷却场的方向偏离到临界角度γ_c处,h_E的大小发生突变,其γ_c的大小随冷却场的增大而增大.特别是当冷却场的偏离角度大于γ_c后,h_E出现由负转正的现象,其转变点还与冷却场的大小有关.另外,h_E与铁磁层原子层数N_F的关系会发生由h_E∝N^-1_F向h_E∝N^-λ_F的转变,其中λ>1.其发生转变的条件与N_F、冷却场大小和方向密切相关. 关键词： 铁磁/反铁磁双层膜 交换偏置 冷却场     

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.     

Bi对自旋阀钉扎场的影响及机理

实验发现将Bi插入自旋阀多层膜TaNiFeCuBi(x)NiFeFeMn中可以显著地提高自旋阀的钉扎场Hex.采用XPS对Cu,Bi元素的分布情况进行了研究,发现Bi的插入明显抑制了Cu原子在自旋阀的制备过程中在NiFeFeMn界面的偏聚.进一步研究表明:自旋阀钉扎层NiFeFeMn界面中,Cu原子的存在是导致自旋阀Hex小于TaNiFeFeMn多层膜Hex的主要原因. 关键词： 自旋阀 钉扎场 交换各向异性 表面活化剂     

NiFe/FeMn双层膜交换偏置的形成及热稳定性研究

研究了在铁磁(NiFe)/反铁磁(FeMn)双层膜之间，交换偏置的形成过程和热稳定性，特别是NiFe/FeMn的交换偏置作用与FeMn层晶粒尺寸的关系.和以前作者不同的是，本文方法采用非磁性Ni-Fe-Cr合金作缓冲层材料，改变Cr的含量就可以获得不同晶粒尺寸的反铁磁FeMn层.实验表明，晶粒尺寸较小的FeMn产生较强的铁磁/反铁磁交换偏置场；但是，对于较大晶粒的FeMn层，出现交换偏置作用所要的临界厚度较小.这符合Mauri提出的理论模型.交换偏置场的热稳定性实验表明，具有较大晶粒尺寸的FeMn层给出较 关键词： 交换偏置 热稳定性 反铁磁 晶粒尺寸     

Exchange bias in nearly perpendicularly coupled ferromagnetic/ferromagnetic system

Exchange bias phenomena appear not only in ferromagnetic/antiferromagnetic systems but also in ferromagnetic/ferromagnetic systems in which two layers are nearly perpendicularly coupled. We investigated the origin of the symmetry-breaking mechanism and the relationship between the exchange bias and the system's energy parameters. We compared the results of computational Monte Carlo simulations with those of theoretical model calculation. We found that the exchange bias exhibited nonlinear behaviors, including sign reversal and singularities. These complicated behaviors were caused by two distinct magnetization processes depending on the interlayer coupling strength. The exchange bias reached a maximum at the transition between the two magnetization processes.     

Influence of magnetic field sweep rate on the hysteresis loops of Ni0.8Fe0.2/Fe0.5Mn0.5 exchange bias bilayer

The influence of the magnetic field sweep rate on the hysteresis loops of exchange bias Ni0.8Fe0.2/Fe0.5Mn0.5 bilayers has been investigated with a vibrating sample magnetometer. It was found that the sweep rate of 13.6 kA/4πms is high enough to bring about obvious changes in the hysteresis loops of the exchange bias bilayer. High sweep rate in the magnetization reversal stage enlarges the coercivity of the sample, while high sweep rate in the saturation state reduces the coercivity. The above phenomena were attributed to magnetic viscosity in the ferromagnetic layer enhanced by the interface exchange interaction and domain magnetization reversals assisted by thermal fluctuation in the antiferromagnetic layer respectively.     

Magnetostriction of FM/TbFe (FM=Fe, Py-permalloy, FeCo) coupled bilayer

Choosing TbFe as the magnetostrictive layer and using soft ferromagnetic materials (FM=Fe, Py-permalloy, FeCo) as the inductive layer, we report the magnetization and magnetostriction of the S/FM(10 nm)/TbFe(10 nm) coupled bilayer (S-glass substrate). The magnetization of the coupled bilayer is attributed to the soft ferromagnetic layer and there is no contribution from the TbFe layer. Interfacial exchange interaction plays an important role in determining the magnetostriction of the coupled bilayer. The effect coming from the deposition Argon pressure on the magnetostriction of the coupled bilayer was also investigated.     

Angular and NiFe thickness dependence of exchange bias in IrMn/NiFe/IrMn thin film

Exchange biased IrMn/NiFe/IrMn thin films were studied as a function of NiFe thickness. In plane angular dependence of a resonance field distribution which is measured by FMR was analyzed as a combined effect of an unidirectional anisotropy and an uniaxial anisotropy. The unidirectional anisotropic field and the uniaxial anisotropic field were linearly varied with NiFe thickness while the films with a thicker NiFe layer do not follow the linear variation. Resonance field and linewidth variations were also analysed with NiFe thickness.     

(Ni0.81Fe0.19)1－xCrx作为种子层对NiFe/PtMn双层膜交换偏置的影响

将NiFe/PtMn双层膜生长在(Ni_0.81Fe_0.19)_1-xCr_x种子层材料上，通过改变种子层中Cr的原子含量，系统的研究了NiFe/PtMn双层膜中PtMn晶粒尺寸和织构对交换偏置的影响.对退火270℃，5h后的NiFe/PtMn双层膜磁性的研究表明,PtMn织构强弱对交换偏置场的影响不明显，而PtMn的晶粒尺寸是影响交换偏置场的主要因素，PtMn颗粒的相干长度在11.3nm左右时得到了较大的交换偏置场. 关键词： NiFe/PtMn双层膜 交换偏置场     

Theoretical investigation of exchange bias

The exchange bias of bilayer magnetic films consisting of ferromagnetic (FM) and antiferromagnetic (AFM) layers in an uncompensated case is studied by use of the many-body Green's function method of quantum statistical theory. The effects of the layer thickness and temperature and the interfacial coupling strength on the exchange bias H_E are investigated. The dependence of the exchange bias H_E on the FM layer thickness and temperature is qualitatively in agreement with experimental results. When temperature varies, both the coercivity H_C and H_E decrease with the temperature increasing. For each FM thickness, there exists a least AFM thickness in which the exchange bias occurs, which is called pinning thickness.     

Asymmetric magnetoresistance in an exchange bias Co/CoO bilayer

Magnetoresistance (MR) measurements are carried out on a Co(8 nm)/CoO(3.5 nm) bilayer in the exchange bias (EB) state prepared by molecular beam epitaxy. With the applied magnetic field parallel to the current, the EB MR curves show an asymmetric behavior about the minimum, in contrast to the symmetric one for non-EB systems. We generalize a well-known analytical expression used for the field dependence of the MR of paramagnets. Our generalization incorporates coercivity and EB in a new phenomenological MR expression. Excellent fits of the latter to the experimental MR data are achieved, showing the way to use MR techniques for the quantitative characterization of EB systems. Furthermore, the temperature dependence of the EB field obtained from MR loops can be described with a power law, which yields a value of 96.6 K for the EB blocking temperature, which is significantly below the Néel temperature of 293 K for bulk CoO.     

引入纳米氧化层的CoFe/Pd双层膜结构中增强的垂直磁各向异性研究

制备了CoFe/Pd双层结构的界面处或CoFe层 内部引入纳米氧化层后的系列薄膜. 研究结果显示, 引入纳米氧化层后, 可以使薄膜的磁各向异性在退火后从面内转到垂直膜面方向. 并且对于在CoFe层内部引入纳米氧化层的这类样品, 其强烈的垂直磁性可以在相当宽的有效磁性层厚度范围内(1.2-2 nm)维持. 在保持垂直磁性的前提下, 这种特殊的双层膜结构中CoFe磁性层厚度比常规CoFe/Pd 多层膜中的CoFe层厚度至少多出1.4 nm. 本文的研究有助于制备出具有较高热稳定性的垂直磁性器件电极.     

Unified nonequilibrium dynamical theory for exchange bias and training effects

We have investigated the exchange bias and training effect in the ferromagnetic/antiferromagnetic (FM/AF) heterostructures using a unified Monte Carlo dynamical approach. The magnetization of the uncompensated AF layer is still open after the first field cycling is finished. Our simulated results show obvious shift of hysteresis loops (exchange bias) and cycling dependence of exchange bias (training effect) when the temperature is below 45~K. The exchange bias field decreases with decreasing cooling rate or increasing temperature and the number of the field cycling. Essentially, these two effects can be explained on the basis of the microscopical coexistence of both reversible and irreversible moment reversals of the AF domains. Our simulations are useful to understand the real magnetization dynamics of such magnetic heterostructures.