摘要
铁磁／反铁磁体系的交换偏置效应在磁电阻传感器和自旋阀方面具有重要的用途,因而也得到了人们的广泛关注.最近一些实验证实：在测量交换偏置场与矫顽场随磁化角度的变化曲线中(以下简称为交换偏置的角度依赖关系)可以观测到阶跃现象.另外,铁磁／反铁磁体系在磁化反转过程中可以表现出半平面转动和全平面转动两种磁化模式.但是,人们并没有说明这些新现象背后的物理机制.本文提出了一种新的方法,详细地分析了铁磁／反铁磁体系的磁化过程,解释了体系在磁化反转过程中出现两种转动磁化模式的机制,也解释了交换偏置角度依赖关系中出现阶跃现象的原因.
根据不施加外磁场时体系的能量与铁磁层磁化强度方向之间的关系,我们将铁磁／反铁磁体系的起始磁化状态分为单稳态、双稳态、三稳态及四稳态共四种不同的状态.将体系出现能量极小与极大时,铁磁层磁化强度的方向分别定义为内禀易轴和内禀难轴.根据内禀易轴与内禀难轴的具体位置将整个磁化方向划分为若干个角度区域.分角度区域地研究体系的磁化过程可以发现,当磁化强度在磁化循环中越过全部的内禀难轴时,铁磁／反铁磁体系在磁化反转过程中将出现全平面转动的磁化模式；当磁化强度在磁化循环中只能越过部分内禀难轴或者根本没有越过任何一个内禀难轴时,铁磁／反铁磁体系在磁化反转过程中将出现半平面转动的磁化模式.外磁场沿内禀易轴和内禀难轴方向磁化时,一支转换场发生突变而另一支转换场则保持连续,最终导致交换偏置场和矫顽场出现阶跃行为.本文利用这种分析方法讨论了各种类型的各向异性对铁磁／反铁磁体系磁化过程的影响,研究了交换偏置场与矫顽场随外磁场磁化角度的变化关系.本论文中的主要结果有：
一、对于仅存在单轴各向异性的铁磁／反铁磁体系.研究表明,通过调节交换各向异性的大小及方向,体系可以在单稳态和双稳态之间相互转换,并且导致交换偏置出现不同形状的角度依赖关系曲线.外磁场沿内禀易轴和内禀难轴方向磁化时,交换偏置场和矫顽场出现了明显的阶跃现象.数值计算表明,交换偏置场和矫顽场在阶跃点处均具有较大的数值.在内禀易轴的阶跃点,矫顽场可以达到最大；在内禀难轴的阶跃点,交换偏置场达到最大而矫顽场可以突然消失.体系在磁化反转过程中可出现半平面转动和全平面转动两种磁化模式,内禀易轴与内禀难轴所在的方向恰是两种转动磁化模式的分界磁化角度.
二、对于存在外应力的铁磁／反铁磁体系.研究表明,调节外应力的大小和方向可以使体系在单稳态和双稳态之间相互转换并导致交换偏置的角度依赖关系发生显著变化.体系存在外应力时,交换偏置的角度依赖关系中仍然存在阶跃现象.外应力可作为一种有效的外部手段来控制和调节铁磁／反铁磁体系的交换偏置,这种调控作用对磁致伸缩系数较大的铁磁层材料将更为明显.
三、对于同时存在单轴和立方各向异性的铁磁／反铁磁体系.研究表明,通过调节立方各向异性的大小和方向,体系将出现单稳态、双稳态、三稳态以及四稳态共计四种状态.存在立方各向异性时,交换偏置将出现复杂的角度依赖关系,表现在交换偏置的角度依赖关系中可以出现非常剧烈的振荡行为.交换偏置场和矫顽场的阶跃行为依然可以在交换偏置的角度依赖关系中出现.体系从单稳态向四稳态变化时,交换偏置角度依赖关系中的阶跃次数逐渐增多；同时发现,增强立方各向异性可以显著提高体系的矫顽力.另外,体系在磁化反转时仍可出现半平面转动和全平面转动两种磁化模式.
四、以平行界面的畴壁模型为基础,研究了反铁磁层的畴壁能对交换偏置角度依赖关系的影响.研究发现,考虑了反铁磁层的畴壁结构之后,交换偏置的角度依赖关系中仍可以出现阶跃现象,同时铁磁／反铁磁体系在磁化过程中仍可以出现全平面转动和半平面转动两种磁化模式.反铁磁层的畴壁能较大时,钉扎角的变化范围较小,反铁磁层可为铁磁层的磁化反转提供稳定的钉扎效果.反铁磁层的畴壁能趋于无穷大时,平行界面的畴壁模型与M-B模型一致.反铁磁层的畴壁能较小时,钉扎角的变化范围较大,反铁磁层对铁磁层的钉扎效果减弱.反铁磁层的畴壁能趋于无穷小时,反铁磁层磁化强度将随铁磁层磁化强度同步转动,铁磁／反铁磁交换偏置体系的磁化性质将与单层铁磁材料相同.
本文是在国家自然科学基金(批准号：10762001),教育部新世纪优秀人才计划基金(批准号：2005-0272),教育部科学技术研究重大项目(批准号：2006024)和高等学校博士学科点专项科研基金(批准号：200801260003)的支持下完成的.
The exchange bias between ferromagnetic/antiferromagnetic systems has received much attention in recent years for its technological importance in magnetoresistive sensors and spin valves. Recently, it has been confirmed by experiments that a jump phenomenon will be emerged in the angular dependence of the exchange bias. Additionally, it is found that the ferromagnetic/antiferromagnetic systems will exhibt the full-plane and half-plane rotation modes in the magnetization reversal processes. However, the mechanism for these new features was not interpreted in these works. In this thesis, a new method was proposed to analyze the magnetization processes of the systems. The magnetization reversal processes of the ferromagnetic/ antiferromagnetic systems have been investigated in detail. The jump phenomenon together with the full-plane and half-plane rotation modes have been explained by this method.
According to the energy spectrum of the systems, it is found that the ferromagnetic/antiferromagnetic systems will be in monostable, bistable, tristable and quadristable states when the applied field is absent at the initial magnetization state. Furthermore, the orientations of ferromagnetic magnetization for the energy minima and energy maxima in the initial magnetization state are defined as the intrinsic easy axes and intrinsic hard axes, respectively. Based on the positions of the intrinsic easy and hard axes, the whole angular range of the magnetization can be divided into several angular regions. The magnetization processes are analyzed when the external field is applied in every angular region. It is found that when the ferromagnetic magnetization crosses the whole of the intrinsic hard axes during the magnetization cycles, the systems will exhibit a full-plane rotation mode during the magnetization reversal processes. Otherwise, the magnetization reversal will show a half-plane rotation mode when the ferromagnetic magnetization crosses partial intrinsic hard axes or it does not cross any intrinsic hard axis in the magnetization cycles. In addition, when the external field is applied along the intrinsic easy and hard axes, it is found that one of the switching fields at the descending or ascending branch of the hysteresis loop makes an abrupt change, while the other switching field keeps continuity, and consequently the exchange bias field and the coercivity will show the jump phenomenon in the angular dependence of the exchange bias. Based on this method, the effect of various anisotropies on the magnetization processes for ferromagnetic/antiferromagnetic systems has been investigated. The dependence of the exchange bias field and the coercivity on the orientation of the applied field has also been investigated in the thesis. Some main results are generalized as follows:
Firstly, only the uniaxial anisotropy is considered in the ferromagnetic/antiferromagnetic systems. By tuning the magnitude and the orientation of the exchange anisotropy, the initial magnetization state of the systems can be divided into monostable state and bistable state, which determine the angular dependence of exchange bias immediately. When the external field is applied along the orientations of the intrinsic easy and hard axes, the exchange bias field and the coercivity will show a jump phenomenon obviously. The numerical calculations indicate that both the exchange bias field and the coercivity are larger in the magnitude at the points of the jump. At the jumping points of the intrinsic easy axes, the coercivity reaches the maximum; at the jumping points of the intrinsic hard axes, the exchange bias field will reach the maximum, at the meantime the coercivity vanishes itself suddenly. The half-plane and full-plane rotation modes will be shown in the magnetization reversal processes, the orientations of the intrinsic easy axes and hard axes are just the critical magnetization angle of these two rotation modes.
Secondly, the effect of the external stress on the exchange bias has been investigated.'Our results demonstrate that both the magnitude and orientation of the external stress will affect the angular dependence of the exchange bias significantly by making a transition between monostable state and bistable state in the systems. The jump phenomenon is also existent in the angular dependence of the exchange bias. The external stress is a viable way to control and tune the exchange bias of the ferromagnetic/antiferromagnetic systems. The effect of the applied stress on the exchange bias will be more remarkable when the ferromagnetic materials have a larger magnetostriction.
Thirdly, both the uniaxial and cubic anisotropies are considered in the ferromagnetic/antiferromagnetic systems. By tuning the relative magnitude and orientation of the cubic anisotropy, the systems will be in monostable, bistable, tristable and quadristable states. It displaces a complex angular dependence of exchange bias in the systems, which manifests itself by a visible oscillation in the curves. The jump phenomenon is also existent in the angular dependence of the exchange bias. Additionally, the half-plane rotation and full-plane rotation modes are also shown in the magnetization reversal processes. The numerical calculations indicate that the coercivity of the system was enhanced significantly by reinforcing the cubic anisotropy, and the times of the jumps are increased in the curves when the systems make the transition from monostable state to quadristable state.
Lastly, the effect of domain wall in the antiferromagnet on the angular dependence of the exchange bias has been investigated based on the planar domain wall model. It is shown that the jump phenomenon is also existent in the angular dependence of the exchange bias. Additionally, the half-plane rotation and full-plane rotation modes are also displaced in the magnetization reversal processes. When the energy of the antiferromagnetic domain wall is larger, the changing range of pinning angle is narrower, which indicates that the better pinning effect of the antiferromagnetic layer is exerted on the ferromagnetic layer. When the energy of the domain wall tends to infinity, the planar domain wall model coincides with the M-B model. On the contrary, if the energy of the antiferromagnetic domain wall is weaker, the changing range of pinning angle is wider, which means a weaker pinning effect exists in the systems. When reducing the energy of the domain wall without limit, the antiferromagnetic magnetization will rotate synchronously with the ferromagnetic magnetization. Therefore, the magnetizing behavior of the exchange-biased ferromagnetic/antiferromagnetic systems will be same to the single ferromagnetic layer.
This work was supported by the National Natural Science Foundation of China (Grant No.10762001), the Program for New Century Excellent Talents in University of China (Grant No.2005-0272), the key project of Chinese ministry of education (grant No.2006024).and the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No.200801260003).
引文
[1]M. N. Baibich, J. M. Broto, A. Fert, F. Nguyen Van Dau, F. petroff, P. Etienne, G Cruezet, A. Friederich, J. Chazelas, Giant Magnetoresistance of (001)Fe/(001)Cr Magnetic Superlattices, Phys. Rev. Lett.,1998, 61(21):2472-2475.
[2]Gbinasch, P. Grunberg, F. Saurenbach, and W. Zinn, Enhanced magnetoresistance in layered magnetic structures with antiferromagnetic interlayer exchange, Phys. Rev. B,1989,39(7):4828-4830.
[3]B. Dieny, V. S. Speriosu, S. S. P. Parkin, B. A. Gurney, D. R. Wilhoit, D. Mauri, Giant magnetoresistive in soft ferromagnetic multilayers, Phys. Rev. B,1991,43(1):1297-1300.
[4]N.Shnerb, Non-Rayleigh statistics of waves in random systems, Phys. Rev. B,1991,43(1):1279-1282.
[5]J. M. Daughton, Y. J. Chen. GMR materials for low field applications. IEEE. Trans. Magn,1993,29(6): 2705-2710.
[6]D. E. Heim, Jr. R. E. Fontana, C. Tsang. Design and operation of spin valve sensors. IEEE. Trans. Magn., 1994,30(2):316-321.
[7]B. Dieny. Giant magnetoresistance in Spin-valve multilayers. J. Magn. Magn. Mater.,1994,136(3): 335-359.
[8]V. Skumryev, S. Stoyanov, Y. Zhang, G. Hadjipanayis, D. Givord, J.Nogues, Beating the superparamagnetic limit with exchange bias, Nature,2003,423(6942),850-853.
[9]S. A. Wolf, D. D. Awschalom, R. A. Buhrman, J. M. Daughton, S. von Molnar, M. L. Roukes, A. Y. Chtchelkanova, and D. M. Treger, Spintronics:A Spin-Based Electronics Vision for the Future, Science, 2001,294(5546):1488-1495.
[10]S. S. P. Parkin, K. P. Roche, M. G. Samant, P. M. Rice, R. B. Beyers, R. E. Scheuerlein, E. J. O'Sullivan, S. L. Brown, J. Bucchigano, D. W. Abraham, Yu Lu, M. Rooks, P. L. Trouilloud, R. A. Wanner, and W. J. Gallagher, Exchange-biased magnetic tunnel junctions and application to nonvolatile magnetic random access memory, J. Appl. Phys.,2000,85(8):5828-58333.
[11]Jian-Gang Zhu, Youfeng Zheng and Gary A. Prinz, Ultrahigh density vertical magnetoresistive random access memory, J. Appl. Phys.,2000,87(9):6668-6673.
[12]Y. Wang, H. Fujiwara and M. Sun, Bias field effects on the toggle mode magnetoresistive random access memory, J. Appl. Phys.,2006,99(7):08N903-1-3.
[13]W. H. Meikljohn, C. P. Bean. New magnetic anisotropy, Phys. Rev.,1957,105(3):904-913.
[14]J. Nogues, I. K. Schuller, Exchange bias, J. Magn. Magn. Mater.,1999,192(2):203-232.
[15]A.E. Berkowitz, Kentaro Takano, Exchange anisotropy -a review, J. Magn. Magn. Mater.,1999,200(1-3): 552-570.
[16]R. L. Stamps, Mechanisms for exchange bias, J. Phys. D,2000,33(23):R247-R268.
[17]M. Kiwi, Exchange bias theory, J. Magn. Magn. Mater.,2001,234(3):584-595.
[18]周仕明,李合印,袁淑娟,王磊,铁磁／反铁磁双层膜中交换偏置,物理学进展,2003,23(1)：62-81.
[19]J. Nogues, J. Sort, V. Langlais, V. Skumryev, S. Surinach, J.S. Munoz, M.D. Baro, Exchange bias in nanostructures, Phys. Rep.,2005,422(3):65-117.
[20]C. Tsang, N. Heiman, and K. Lee, Exchange induced unidirectional anisotropy at FeMn-Ni80Fe20 interfaces, J. Appl. Phys.,1981,52(3):2471-2473.
[21]R. Jungblut, R. Coehoorn, M. T. Johnson, J. aan de Stegge, and A. Reinders, Orientational dependence of the exchange biasing in molecular-beam-epitaxy-grown Ni80Fe2o/Fe5oMn5o bilayers, J. Appl. Phys.,1994, 75(10):6659-6664.
[22]A.P.Malozemoff, Random-field model of exchange anisotropy at rough ferromagnetic-antiferromagnetic interfaces, Phys. Rev. B,1987,35(7):3679-3682.
[23]V. Speriosu, S. S. P Parkin, C. H. Wilts, Standing spin waves in FeMn/NiFe/FeMn exchange-bias structures, IEEE. Trans. Magn,1987,23(5):2999-3001.
[24]S. Zhang, D. V. Dimitrov, G. C. Hadjipanayis, J. W. Cai and C. L. Chien, Coercivity induced by random field at ferromagnetic and antiferromagnetic interfaces, J. Magn. Magn. Mater.,1999,199(1-3):468-470.
[25]Y. J. Tang, B. Roos, T. Mewes, S. O. Demokritov, B. Hillebrands, Y. J. Wang, Enhanced coercivity of exchange-bias Fe/MnPd bilayers, Appl. Phys. Lett.,1999,75(5):707-709.
[26]D. Mauri, E. Kay, D. Scholl and J.K. Howard, Novel method for determining the anisotropy constant of MnFe in a NiFe/MnFe sandwich, J. Appl. Phys.,1987,62(7):2929-2932.
[27]N. J. Gokemeijer, R. L. Penn and D. R. Veblen, C. L. Chien, Exchange coupling in epitaxial CoO/NiFe bilayers with compensated and uncompensated interfacial spin structures, Phys. Rev. B,2001,63(17): 174422-1-4.
[28]S.L, Burkett, S. Kora, J.C. Lusth, Annealing of spin valves with high exchange pinning fields, IEEE. Trans. Magn,1997,33(5):3544-3546.
[29]A. P. Malozemoff, Random-field model of exchange anisotropy at rough ferromagnetic-antiferromagnetic interfaces, Phys. Rev. B,1987,35(7):3679-3682.
[30]J. Nogues, D. Lederman, T. J. Moran, I. K. Schuller, and K. V. Rao, Large exchange bias and its connection to interface structure in FeF2-Fe bilayers, Appl. Phys. Lett.,1996,68(22):3186-3188.
[31]J.X. Shen, M. T. Kief, Exchange coupling between NiO and NiFe thin films, J. Appl.Phys.1996,79(8): 5008-5010.
[32]D.G Hwang, S. S. Lee, C. M. Park, Effect of roughness slope on exchange biasing in NiO spin valves, IEEE. Trans. Magn,1998,72(17):2162-2164.
[33]D. Lederman, J. Nogues, and Ivan K. Schuller, Exchange anisotropy and the antiferromagnetic surface order parameter, Phys. Rev. B,1997,56(5):2332-2335.
[34]S. Soeya, M. Fuyama, S. Tadokoro, T. Imagawa, NiO structure-exchange anisotropy relation in the Ni81Fe19/NiO films and thermal stability of NiO film. J. Appl. Phys.,1996,79(3):1604-1610.
[35]A. M. Choukh, Effect of interface on exchange coupling in NiFe/FeMn system, IEEE. Trans. Magn,1997, 33(5):3676-3678.
[36]T. J. Moran, J. M. Gallego, I. K. Schuller, Increased exchange anisotropy due to disorder at permalloy/CoO interfaces, J. Appl. Phys.,1995,78(3):1887-1891.
[37]N.C.Koon, Calculations of Exchange Bias in Thin Films with Ferromagnetic/Antiferromagnetic Interfaces, Phys. Rev. lett.,1997,78(25):4865-4868.
[38]Joo-Von Kim, R.L.Stamps, B.V.Mcgrath and R.E.Camley, Angular dependence and interfacial roughness in exchange-biased ferromagnetic/antiferromagnetic bilayers, Phys. Rev. B,2000,61(13):8888-8894.
[39]Joo-Von Kim, R. L. Stamps, Defect Modified Exchange Bias, Appl. Phys. Lett.,2001,79(17):2785-2787.
[40]D. Guarisco, E. Kay, S.X. Wang, In situ and ex situ observation of spin valves obtained by ion-beam deposition, IEEE. Trans. Magn,1997,33(5):3595-3597.
[41]S. Gangopadhyay, G. C. Hadjipanayis, C. M. Sorensen, K. J. Klabunde, Magnetic properties of ultrafine Co particles, IEEE. Trans. Magn,1992,28(5):3174-3176.
[42]T. Umemoto, A. Maeda, S. Takahashi, T. Tanuma, M. Kume, Physical Properties of CoFe/IrMn Spin-Valves Prepared Using Ion Beam Sputtering with an Xe-H2 Mixture Gas, Jpn. J. Appl. Phys.1997,36(11): 6746-6748.
[43]C. H. Lai, T. C. Anthony, R. Iwamura, R. L. White, The effect of microstructure and interface conditions on
the anisotropic exchange fields of NiO/NiFe, IEEE. Trans. Magn,1996,32(5):3419-3421.
[44]Li Tang, David E. Laughlin, Sunita Gangopadhyay, Microstructural study of ion-beam deposited giant magnetoresistive spin valves, J. Appl. Phys.1997,81(8):4906-4908.
[45]K. Uneyama, M. Tsunoda, M. Takahashi, Influence of gas adsorption at the interface on the exchange coupling field of Ni-Fe/25at%Ni-Mn/Ni-Fe films, IEEE. Trans. Magn,1997,33(5):3685-3687.
[46]K. Takano, R. H. Kodama, A. E. Berkowitz, W. Cao and G. Thomas, Interfacial Uncompensated Antiferromagnetic Spins:Role in Unidirectional Anisotropy in Polycrystalline Ni81Fej9/CoO Bilayers, Phys. Rev.Lett.,79(6):1130-1133.
[47]Seongtae Bae, Jack H. Judy, W. F. Egelhoff, P. J. Chen, Dependence of exchange coupling on the surface roughness and structure in a-Fe2O3/NiFe and NiFe/a-Fe2O3 bilayers, J. Appl. Phys.1997,87(9):6650-6652.
[48]T. Ambrose and C. L. Chien, Dependence of exchange coupling on antiferromagnetic layer thickness in NiFe/CoO bilayers, J. Appl. Phys.1998,83(11):6822-6824.
[49]P. J. van der Zaag, Y. Ijiri, J. A. Borchers, L. F. Feiner, R. M. Wolf, J. M. Gaines, R.W. Erwin, and M. A. Verheijen, Difference between Blocking and Neel Temperatures in the Exchange Biased Fe3O4/CoO System, Phys. Rev. Lett.,2000,84(26):6102-6105.
[50]T. Ambrose, C. L. Chien, Dependence of exchange field and coercivity on cooling field in NiFe/CoO bilayers, J. Appl. Phys.1998,83(11):7222-7224.
[51]J. Olamit, Z. P. Li, I. K. Schuller, K. Liu, Angular dependence of exchange anisotropy on the cooling field in ferromagnet/fluoride thin films, Phys. Rev. B,2006,73(2):024413-1-7.
[52]J. Nogues, D. Lederman, T. J. Moran, Ivan K. Schuller, Positive Exchange Bias in FeF2-Fe Bilayers, Phys. Rev. Lett.,1996,76(24):4624-4627.
[53]J. Nogues, C. Leighton, I. K. Schuller, Correlation between antiferromagnetic interface coupling and positive exchange bias, Phys. Rev. B,2000,61(2):1315-1317.
[54]D. Z. Yang, J. Du, L. Sun X. S. Wu, X. X. Zhang, S. M. Zhou, Positive exchange biasing in GdFe/NiCoO bilayers with antiferromagnetic coupling, Phys. Rev. B,2005,71(14):144417-1-5.
[55]W. Zhu, L. Seve, R. Sears, B. Sinkovic, S. S. P. Parkin, Field Cooling Induced Changes in the Antiferromagnetic Structure of NiO Films, Phys. Rev. Lett.,2001,86(23):5389-5392.
[56]M. Kiwi, J. Meij a-Lopez, R. D. Portugal, R. Ramirez, Exchange-bias systems with compensated interfaces, Appl. Phys. Lett.,75(25):3995-3997.
[57]D. Schafer D, J. Geshev, S. Nicolodi, L.G Pereira, J. E. Schmidt, P. L. Grande, Controlled rotation of the exchange-bias direction in IrMn/Cu/Co via ion irradiation, Appl. Phys. Lett.,2008,93(4):042501-1-3.
[58]D. N. H. Nam, W. Chen, K.G. West, D. M. Kirkwood, J. Lu, S. A. Wolf, Propagation of exchange bias in CoFe/FeMn/CoFe trilayers, Appl. Phys.Lett.,2008,93(15):152504-1-3.
[59]H. Ohldag, A. Scholl, F. Nolting, E. Arenholz, S. Maat, A.T. Young, M. Carey, J. Stohr, Correlation between Exchange Bias and Pinned Interfacial Spins, Phys. Rev. Lett.,2003,91(1):017203-1-4.
[60]D. Mauri, H. C. Siegmann, P. S. Bagus, Simple model for thin ferromagnetic films exchange coupled to an antiferromagnetic substrate, J. Appl. Phys.,1987,62(7):3047-3049.
[61]F. Y. Yang, C. L. Chien, Spiraling Spin Structure in an Exchange-Coupled Antiferromagnetic Layer, Phys. Rev. Lett.,2000,85(12):2597-2600.
[62]A. P. Malozemoff, Heisenberg-to-Ising crossover in a random-field model with uniaxial anisotropy, Phys. Rev. B,1988,37(13):7673-7679.
[63]A. P. Malozemoff, Mechanisms of exchange anisotropy, J. Appl. Phys.,1987,63(8):3874-3879.
[64]J. A. Borchers, Y. Ijiri, D. M. Lind, P. G. Ivanov, R. W. Erwin, S. H. Lee, C. F. Majkrzak,, Polarized neutron diffraction studies of exchange-coupled Fe3O4/NiO superlattices, J. Appl. Phys.,1999,85(8):5883-5995.
[65]Y. Ijiri, J. A. Borchers, R. W. Erwin, S.H. Lee, P. J. van der Zaag, R. M. Wolf, Perpendicular Coupling in Exchange-Biased Fe3O4/CoO Superlattices, Phys. Rev. Lett.,1998,80(3):608-611.
[66]T.C. Schulthess, W.H.Butler. Consequences of Spin-Flop Coupling in Exchange Biased Films. Phys. Rev. lett.,1998,81(20):4516-4519.
[67]Chih-Huang Lai, Hideo Matsuyama, Robert L. White, Thomas C, Anthony, Gary G. Bush, Exploration of magnetization reversal and coercivity of epitaxial NiO{111}/NiFe films, J. Appl. Phys.,1996,79(8): 6389-6391.
[68]D. Paccard, C. Schlenker, O. Massenet, R. Montmory, A. Yelon, A New Property of Ferromagnetic-Antiferromagnetic Coupling, Phys. Status.Solidi,1996,16(1):301-311.
[69]W. Stoecklein, S. S. P. Parkin, J. C. Scott, Ferromagnetic resonance studies of exchange-biased Permalloy thin films, Phys. Rev. B,1988,38(10):6847-6854.
[70]R. D. McMichael, M. D. Stiles, P. J. Chen, W. F. Egelhoff, Jr., Ferromagnetic resonance studies of NiO-coupled thin films of Ni80Fe20, Phys. Rev. B,1988,58(13):8605-8612.
[71]R. D. McMichael, W.F. Jr. Egelhoff, L.H Bennett, Thermal degradation of exchange biased films in spin-valves, IEEE. Trans. Magn,1996,31(6):3930-3932.
[72]S. M. Zhou, S. J. Yuan, L. Wang,M. Lu, J. Du, A. Hu, J. T. Song, Positive isotropic resonance field shift of exchange coupled wedged-permalloyOFeMn bilayers, Appl. Phys. Lett.,2003,83(10):2013-2015.
[73]Isotropic ferromagnetic resonance field shift in as-prepared permalloy/FeMn bilayers, Eur. Phys. J. B,2005, 44(4):557-562.
[74]M. R. Fitzsimmons, P. Yashar, C. Leighton, Ivan K. Schuller, J. Nogues, C. F. Majkrzak, J. A. Dura, Asymmetric Magnetization Reversal in Exchange-Biased Hysteresis Loops, Phys. Rev. Lett.,2000,84(17): 3986-3989.
[75]E. Girgis, R. D. Portugal, H. Loosvelt, M. J. Van Bael, I. Gordon, M. Malfait, K. Temst, C. Van Haesendonck, L. H. A. Leunissen, R. Jonckheere, Enhanced Asymmetric Magnetization Reversal in Nanoscale Co/CoO Arrays:Competition between Exchange Bias and Magnetostatic Coupling, Phys. Rev. Lett.,2003,91(18):187202-1-4.
[76]P. Gogol, J. N. Chapman, M. F. Gillies, F. W. M, Vanhelmont, Domain processes in the magnetization reversal of exchange-biased IrMn/CoFe bilayers, J. Appl. Phys.,2002,92(3):1458-1465.
[77]A. Kirilyuk, Th. Rasing, H. Jaffre s, D. Lacour, F. Nguyen Van Dau, Domain structures during magnetization reversal in exchange-biased layers, J. Appl. Phys.,2002,91(10):7745-7747.
[78]B. Beckmann, U. Nowak, and K. D. Usadel, Asymmetric Reversal Modes in Ferromagnetic/Antiferromagnetic Multilayers, Phys. Rev. Lett.,2003,91(18):187201-1-4.
[79]P. Blomqvist, Kannan M. Krishnan, H. Ohldag, Direct Imaging of Asymmetric Magnetization Reversal in Exchange-Biased Fe/MnPd Bilayers by X-Ray Photoemission Electron Microscopy, Phys. Rev. Lett.,2005, 94(10):107203-1-4.
[80]Steven Brems, Kristiaan Temst, Chris Van Haesendonck, Origin of the Training Effect and Asymmetry of the Magnetization in Polycrystalline Exchange Bias Systems, Phys. Rev. Lett.,2007,99(06):067201-1-4.
[81]Haiwen Xi, Robert M. White, Sergio M. Rezende, Irreversible and reversible measurements of exchange anisotropy, Phys. Rev. B,1999,60(21):14837-14840.
[82]J. R. Fermin, M. A. Lucena, A. Azevedo, F. M. de Aguiar, S. M. Rezende, Measurements of exchange anisotropy in NiFe/NiO films with different techniques, J. Appl. Phys.,2000,87(9):6421-6423.
[83]Haiwen Xi, Robert M. White, Sergio M. Rezende, Measurement dependence of the exchange bias, J. Appl. Phys.,2000,87(9):4960-4962.
[84]J. Geshev, L. G. Pereira, J. E. Schmidt, Angular dependence of the exchange bias obtained from magnetization and ferromagnetic resonance measurements in exchange-coupled bilayers, Phys. Rev. B,2000, 64(18):184411-1-5.
[85]J.Geshev, Analytical solutions for exchange bias and coercivity in ferromagnetic/antiferromagnetic bilayers, Phys. Rev. B,2000,62(9):5627-5633.
[86]R.L.Rodrnguez-Suarez, L. H. Vilela Leao, F. M. de Aguiar, S. M. Rezende, A. Azevedo,Exchange anisotropy determined by magnetic field dependence of ac susceptibility, J. Appl. Phys.,2003,94(7): 4544-4550.
[87]J. Geshev, S. Nicolodi, L. G. Pereira, L. C. C. M. Nagamine, J. E. Schmidt, C. Deranlot, F. Petroff, R. L. Rodriguez-Suarez, A. Azevedo, Exchange bias through a Cu interlayer in an IrMn/Co system Phys. Rev. B, 2007,75(21):214402-1-5.
[88]Kai Liu, Shenda M. Baker, Mark Tuominen, Thomas P. Russell, Ivan K. Schullerl, Tailoring exchange bias with magnetic nanostructures, Phys.Rev.B,2001,63(6):060403-1-4.
[89]A. Hoffmann, Symmetry Driven Irreversibilities at Ferromagnetic-Antiferromagnetic Interfaces, Phys. Rev. Lett.,2004,93(9):097203-1-4.
[90]E. Pina,C. Prados, A. Hernando, Large training effects in magnetic relaxation and anisotropic magnetoresistance in nanocrystallineexchange-biased Ni8oFe20/CoO bilayers, Phys. Rev. B,2004,69(9): 052402-1-4.
[91]T. Hauet, S. Mangin, J. McCord, F. Montaigne, Eric E. Fullerton, Exchange-bias training effect in TbFe/GdFe:Micromagnetic mechanism, Phys.Rev.B,2007,76(9):144423-1-4.
[92]Steven Brems, Alexander Volodin, Chris Van Haesendonck, Kristiaan Temst, Magnetic force microscopy study of the training effect in polycrystalline Co/CoO bilayers, J.Appl.Phys.,2008,103(11):113912-1-4.
[93]M. K. Chan, J. S. Parker, P. A. Crowell, C. Leighton, Identification and separation of two distinct contributions to the training effect in polycrystalline Co/FeMn bilayers, Phys.Rev.B,2008,77(1): 014420-1-5.
[94]Paolo Biagioni, Antonio Montano, Marco Finazzi, Influence of three-dimensional dynamics on the training effect in ferromagnet-antiferromagnet bilayers, Phys. Rev. B,2009,80(13):134401-1-7.
[95]S. Maat, K. Takano, S. S. P. Parkin, Eric E. Fullerton,Perpendicular Exchange Bias of Co/Pt Multilayers, Phys. Rev. Lett.,2001,87(8):087202-1-4.
[96]Haiwen Xi, T. F. Ambrose, T. J. Klemmer, R. van de Veerdonk, J. K. Howard, Robert M. White, Perpendicular magnetization and exchange bias in epitaxial Cu/Ni/Fe50Mn50 thin films, Phys.Rev.B, 2005,72(2):024447-1-6.
[97]Z. Shi, X. P. Qiu, S. M. Zhou, X. J. Bai, J. Du, Anomalous training effect of perpendicular exchange bias in Pt/Co/Pt/IrMn multilayers, Appl. Phys. Lett.,2008,93(22):222504-1-3.
[98]Y. Nie, W. W. Lin, M. Huang, K. X. Xie, J. Du, H. Sang, G Xiao, Angular dependence of magnetization reversal in exchange-biased Co/Pt multilayer with perpendicular magnetic anisotropy, J. Appl. Phys.,2008, 103(7):07C110-1-3.
[99]Ildico L. Guhr, Olav Hellwig, Christoph Brombacher, Manfred Albrecht, Observation of perpendicular exchange bias in [Pd/Co]-CoO nanostructures:Dependence on size, cooling field, and training, Phys. Rev. B, 2007,76(6):064434-1-6.
[100]S. J. Lee, J. P. Goff, G. J. McIntyre, R. C. C. Ward, S. Langridge, T. Charlton, R. Dalgliesh, D. Mannix, Perpendicular Antiferromagnetic Ordering of Mn and Exchange Anisotropy in Fe/Mn Multilayers, Phys. Rev. Lett.,2007,99(3):037204-1-4.
[101]T. Ambrose, R.T. Sommer, C. L. Chien, Angular dependence of exchange Coupling in ferromag-net/antiferromagnet bilayers, Phys. Rev. B,1997,56(1):83-86.
[102]Haiwen Xi, M. H. Kryder, R. M. White, Study of the angular-dependent exchange coupling between a ferromagnetic and an antiferromagnetic layer, Appl. Phys. Lett.,1999,74(18):2687-2689.
[103]Haiwen Xi, R. M. White, Angular dependence of exchange anisotropy in Ni81Fe19/CrMnPtx bilayers, J. Appl.
Phys.,1999,86(9):5169-5174.
[104]Dong Young Kim, CheolGi Kim, Chong-Oh Kim, M. Tsunoda, M. Takahashi, Angular dependence of exchange bias and coercivity in polycrystalline CoFe/MnIr bilayers. J. Magn. Magn. Mater.,2006,304(1): e56-e58.
[105]D. Spenato, V. Castel, S.P. Pogossian, S P, D. T. Dekadjevi, J. Ben Youssef, Asymmetric magnetization reversal behavior in exchange-biased NiFe/MnPt bilayers in two different anisotropy regimes:Close and far from critical thickness, Appl. Phys. Lett.,2007,91(6):062515-1-3.
[106]J. Camarero, J.Sort, A. Hoffmann, J. M. Garcia-Martin, B. Dieny, R. Miranda, J. Nogues, Origin of the Asymmetric Magnetization Reversal Behavior in Exchange-Biased Systems:Competing Anisotropies, Phys. Rev. Lett.,2005,95(5):057204-1-4.
[107]P. Y. Yang, C. Song, B. Fan, F. Zeng, F. Pan, The role of rotatable anisotropy in the asymmetric magnetization reversal of exchange biased NiO/Ni bilayers, J. Appl. Phys.,2009,106(1):013902-1-7.
[108]Liedke M O, Liedke B, Keller A, et al. Induced anisotropies in exchange-coupled systems on rippled substrates. Phys Rev B,2007,75(22):220407-1-4.
[109]S. H. Chung, A. Hoffmann, M. Grimsditch, Interplay between exchange bias and uniaxial anisotropy in a ferromagnetic/antiferromagnetic exchange-coupled system, Phys. Rev. B,2005,71(21):214430-1-10.
[110]E.C. Stoner, E. P. Wohlfarth, A mechanism of magnetic hysteresis in heterogeneous alloys, IEEE. Trans. Magn.,1991,27(4):3475-3518.
[111]E. Jimenez, J. Camarero, J. Sort, J. Nogues, A. Hoffmann, F. J. Teran, P. Perna, J. M. Garcia-Martin, B. Dieny, R. Miranda, Highly asymmetric magnetic behavior in exchange biased systems induced by noncollinear field cooling, Appl. Phys. Lett.,2009,95(12):122508-1-3.
[112]T. Mewes, H. Nembach, M.Rickart, S. O. Demokritov, J. Fassbender, B. Hillebrands, Angular dependence and phase diagrams of exchange-coupled epitaxial Nig1Fe19/Fe5oMn5o (001) bilayers, Phys. Rev. B.,2001, 65(22):224423-1-7.
[113]T. Mewes, H. Nembach, M. Rickart, B. Hillebrands, Separation of the first-and second-order contributions in magneto-optic Kerr effect magnetometry of epitaxial FeMnONiFe bilayers, J. Appl. Phys.,2004,95(10): 5324-5329.
[114]T. Blachowicz, A. Tillmanns, M. Fraune, R. Ghadimi, B. Beschoten, G Giintherodt, Exchange bias in epitaxial CoO/Co bilayer with different crystallographic symmetries, Phys. Rev. B.,2007,75(5): 054425-1-8.
[115]Dong Young Kim, Cheol Gi Kim, Chong-Oh Kim, M. Shibata, M. Tsunoda, M. Takahashi, Angular Dependence of Exchange Bias and Coercive Field in CoFe/MnIr Epitaxial Bilayers, IEEE. Trans.Magn., 2005,41(10):2712-2714.
[116]A. Tillmanns, S. Oertker, B. Beschoten, G Guntherodt, J. Eisenmenger, I. K. Schuller, Angular dependence and origin of asymmetric magnetization reversal in exchange-biased Fe/FeF2(110), Phys. Rev. B,2008, 78(1):012401-1-4.
[117]Y. J. Tang, B. F. P. Roos, T. Mewes, A. R. Frank, M. Rickart, M. Bauer, S. O. Demokritov, B. Hillebrands, X. Zhou, B. Q. Liang, X. Chen, W. S. Zhan, Structure and magnetic properties of exchange-biased polycrystalline FeOMnPd bilayers, Phys. Rev. B,2000,62(13):8654-8657.
[118]Michael J. Pechan, Douglas Bennett, Nienchtze Teng, C. Leighton, J. Nogues, Ivan K. Schuller, Induced anisotropy and positive exchange bias:A temperature, angular, and cooling field study by ferromagnetic resonance, Phys. Rev. B,2002,65(6):064410-1-5.
[119]Chih-Huang Lai, Yung-Hung Wang, Ching-Ray Chang, Jyh-Shinn Yang, Y. D. Yao, Exchange-bias-induced double-shifted magnetization curves in Co biaxial films, Phys. Rev. B,2001,64(9):094420-1-5.
[120]Zhi-Hong Wang, G. Cristiani, H.-U. Habermeier, J. A. C. Bland, Double magnetic switching, domain wall
processes, and interfacial exchange coupling in an exchange-biased bilayer film, Phys. Rev. B,72(5): 054407-1-7.
[121]S. Dubourg, J. F. Bobo, B.Warot, E. Snoeck, J. C. Ousset, Complex angular dependence of the exchange bias on (001) epitaxial NiO-Co bilayers, Eur. Phys. J. B,2005,45(6):175-179.
[122]A. Hoffmann, M. Grimsditch, J.E. Pearson, J.Nogues, W.A.A. Macedo, I.K.Schuller, Tailoring the exchange bias via shape anisotropy in ferromagnetic/antiferromagnetic exchange-coupled systems, Phys. Rev. B,2003, 67(22):220406-1-4.
[123]Z. Y. Liu, S. Adenwalla, Angular dependence of magnetization reversal process in exchange coupled ferromagnetic/antiferromagnetic bilayers, J. Appl. Phys.,2003,93(6):3422-3426.
[124]P. V. Mitchell, K. R. Mountfield, J. O. Artman, Stress-Induced Anisotropy in Co-CrThin Film, J. Appl. Phys., 1988,63(8):2917-2919.
[125]D. Garcia, F. J. Castano, M. Vazquez, C. Prados, F. Castano, Crossed Anisotropies In FeB/CoSiB Bilayers Induced by the Bowed-Sub-Strate Sputtering Technique, Appl. Phys. Lett.,1999,74(1):105-107.
[126]D. Sander D, the correlation between Mechanical stress and Magnetic anisotropy in Ultrathin Films, Rep., Prog., Phys.,1999,62(5):809-858.
[127]Jian Hong Rong, GuoHong Yun, B. Narsu, D. W. L. Sprung, Ferromagnetic resonance and stress anisotropy in a ferromagnetic/anti-ferromagnetic bilayer, J. Appl. Phys,2006,100(8):083901-1-6.
[128]L. Kraus, V. Haslar, K. Zaveta, J. Pokorny, P. Duhaj, C. polak, An amorphous magnetic bimetallic sensor material, J. Appl. Phys,1995,78(10):6157-6164.
[129]Chih-Huang Lai, shing-An Chen, J.C.A. Huang, thickness effect on stress-induced exchange anisotropy of NiFe/NiFeMn, J. Appl. Phys.,87(9):6556-6658.
[130]D. H. Han, J. G. Zhu, J. H. Judy, J. M. Sivertsen, Stress effects on exchange coupling field, coercivity, and uniaxialanisotropy field of NiO/NiFe bilayer thin film for spin valves, J. Appl. Phys.,1997,81(8): 4519-4521.
[131]D. H. Han, J. G. Zhu, J. H. Judy, J. M. Sivertsen, Effect of stress on exchange coupling field, coercivity, and uniaxial anisotropy field of NiFe/NiO, Appl. Phys. Lett.,1997,70(5):664-666.
[132]Jing Pan, Yong-chunTao, Lan Zhou, Jing-guo Hu, The Exchange Anisotropy in Ferromagnetic/Antiferromagnetic Bilayers under the Strain Field, Jpn. J. Appl. Phys.2007,46(10): 6613-6617.
[133]C. Le Graet, D. Spenato, S. P. Pogossian, D. T. Dekadjevi, J. Ben Youssefa, Probing misalignment in exchange biased systems:A dynamic approach, Appl. Phys. Lett.,2009,94(26):262502-1-3.
[134]E. Jimenez, J. Camarero, J. Sort, J. Nogues, N. Mikuszeit, J. M. Garcia-Martin, A. Hoffmann, B. Dieny, R. Miranda, Emergence of noncollinear anisotropies from interfacial magnetic frustration in exchange-bias systems, Phys. Rev. B,2009,80(1):014415-1-7.
[135]J. McCord, C.Hamann, R. Schafer, L. Schultz, R. Mattheis, Nonlinear exchange coupling and magnetic domain asymmetry in ferromagnetic/IrMn thin films, Phys. Rev. B,2008,78(9):094419-1-8.
[136]A. Thiaville, Extensions of the geometric solution of the two dimensional coherent magnetization rotation model, J. Magn. Magn. Mater.,1998,182(1):5-18.
[137]Haiwen Xi, Robert M. White, Critical thickness effect in the exchange-coupled NiFe/CrMnPtx bilayer system, J. Appl. Phys.,2000,61(2):1318-1323.
[138]J. Geshev, S.Nicolodi, L. G. Pereira, J. E. Schmidt, V. Skumryev, S. Surinach, M. D. Baro, Impact of magnetization easy-axis distributions on the ferromagnet-antiferromagnet exchange-coupling estimation, Phys. Rev. B,2008,77(13):132407-1-4.