CN106098083B - 隧穿磁阻器件和隧穿磁阻读头 - Google Patents

隧穿磁阻器件和隧穿磁阻读头 Download PDF

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CN106098083B
CN106098083B CN201610283732.5A CN201610283732A CN106098083B CN 106098083 B CN106098083 B CN 106098083B CN 201610283732 A CN201610283732 A CN 201610283732A CN 106098083 B CN106098083 B CN 106098083B
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Z.高
S.吴
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Abstract

本公开提供了隧穿磁阻器件和隧穿磁阻读头。隧穿磁阻(TMR)器件具有薄的MgO隧穿势垒层和自由铁磁多层。自由铁磁多层包括CoFeB第一铁磁层、具有负磁致伸缩的面心立方(fcc)NiFe补偿层、以及在CoFeB层和fcc NiFe补偿层之间的体心立方(bcc)NiFe插入层。可选的铁磁纳米层可以位于MgO势垒层和CoFeB层之间。可选的非晶分隔层可以位于CoFeB层和bcc NiFe插入层之间。bcc NiFe插入层(以及可选的非晶分隔层，如果使用的话)防止fcc NiFe层在退火期间不利地影响MgO层和CoFeB层的晶体形成。bcc NiFe插入层还增大TMR并降低自由铁磁多层的Gilbert阻尼常数。

Description

隧穿磁阻器件和隧穿磁阻读头
技术领域
本发明总体地涉及隧穿磁阻(TMR)器件，更具体地，涉及具有氧化镁(MgO)隧穿势垒层的TMR读头。
背景技术
隧穿磁阻(TMR)器件，也被称为磁隧道结(MTJ)器件，由通过薄的绝缘隧穿势垒层分隔的两个铁磁层构成。势垒层通常由金属氧化物制成，该金属氧化物足够薄使得在这两个铁磁层之间发生载流子的量子力学隧穿。尽管已经提出各种金属氧化物诸如铝氧化物(Al2O3)和钛氧化物(TiO2)作为隧穿势垒材料，但是最有前景的材料是晶体氧化镁(MgO)。量子力学隧穿过程是依赖电子自旋的，这表示当跨过结(junction)施加感测电流时测量的电阻取决于铁磁层和势垒层的自旋相关(spin-dependent)电子性质，并且是这两个铁磁层的磁化的相对取向的函数。铁磁层中的一个(被称为参考层)的磁化被固定或者被钉扎，而另一铁磁层(被称为自由层)的磁化是自由的以响应于外部磁场而旋转。它们的磁化的相对取向随外部磁场而变化，因此导致电阻的变化。TMR器件可用作非易失性磁随机存取存储器(MRAM)阵列中的存储器单元以及可用作磁记录盘驱动器中的TMR读头。
图1示出常规TMR读头10的截面图。TMR读头10包括底部的被“固定”或“被钉扎”的参考铁磁(FM)层18、绝缘隧穿势垒层20以及顶部“自由”FM层32。TMR读头10分别具有底部和顶部非磁性电极或引线12、14，底部非磁性电极12形成在适合的基板上。FM层18被称作参考层，因为当存在对于TMR器件的感兴趣的期望范围内的施加磁场(即，来自磁记录盘中的磁性层的记录区域的磁场)的情况下，该FM层18的磁化被防止旋转。参考FM层18的磁化可以通过由高矫顽磁性膜形成或者通过交换耦合到反铁磁(AF)“钉扎”层而被固定或者被钉扎。参考FM层18可以是反平行(AP)被钉扎结构或者磁通闭合结构(flux-closure structure)的一部分，其中两个铁磁层通过反平行耦合(APC)间隔层而分隔并因此被反平行耦合以形成磁通闭合，如在US5465185中所描述的。自由FM层32的磁化是自由的从而在感兴趣的范围内的施加磁场存在的情况下旋转。在没有施加的磁场的情况下，FM层18和32的磁化一般在TMR读头10中垂直地排列。FM层18、32的磁化的相对取向确定TMR器件的电阻。
像CoFe/MgO/CoFe器件一样，具有MgO隧穿势垒的TMR器件由于某种对称性的电子的相干隧穿(coherent tunneling)而表现出非常大的磁阻。然而，MgO隧道结需要具有(001)外延和理想的结晶度。MgO势垒层通常通过溅射沉积和随后的退火而形成，这形成晶体结构。已经发现，当硼(B)用于参考铁磁层和自由铁磁层中的一个或多个中时，在退火之后观察到较高的隧穿磁阻(ΔR/R或者TMR)。已知非晶的CoFeB层促进MgO在(001)方向的高质量结晶，因此实现更高的TMR。
在TMR读头中，自由铁磁层应当产生高的TMR和低的磁致伸缩。自由层通常是包括靠近MgO势垒层的如CoFe或者CoFeB的第一铁磁层的多层，该第一铁磁层通常具有高的自旋极化而且具有高的正磁致伸缩。为了对此进行补偿，自由多层还包括具有负磁致伸缩和低Fe含量(通常小于约15原子百分比(at.％))的相对厚的NiFe合金层作为第二铁磁层。然而，低Fe的NiFe第二层具有面心立方(fcc)晶体结构，其破坏在退火之后MgO势垒与第一自由层之间的外延关系。这导致低的TMR。为了减轻此问题，非晶的分隔层如Ta可以形成在第一层和第二层之间。还提出了铁磁非晶分隔层如CoFeBTa，如US 8427791B2中描述的，其被转让给与本申请相同的受让人。然而，这些非晶分隔层会导致自由层具有高的Gilbert阻尼常数(参数α，其是公知的Landau-Lifshitz-Gilbert公式中的无量纲系数)。高阻尼导致高的热致磁噪声(有时被称为“磁噪声(mag-noise)”)。随着自由层体积(并且因此其磁能)减小，热激发对自由层的影响变得越来越重要。由于磁噪声还与TMR信号成比例，所以如果TMR大则磁噪声是TMR器件中的主要噪声源，并将限制可实现的信噪比(SNR)。因此，期望设计具有低阻尼的TMR器件使得磁噪声被抑制。
所需要的是具有高TMR的TMR器件，其具有MgO势垒层和自由层，该自由层具有低磁致伸缩和低阻尼。
发明内容
本公开提供具有氧化镁隧穿势垒层和带有插入层的自由层的隧穿磁阻(TMR)器件。
本发明的实施方式涉及具有薄的MgO隧穿势垒层和自由铁磁多层的TMR器件。自由铁磁多层包括CoFeB第一铁磁层、具有负磁致伸缩的基本上面心立方(fcc)的低Fe的NiFe补偿层、以及在CoFeB第一铁磁层和fcc NiFe补偿层之间的基本上体心立方(bcc)的高Fe的NiFe插入层。可选的Co、Fe或CoFe纳米层可以位于MgO势垒层和CoFeB第一铁磁层之间。可选的非晶分隔层如Ta、CoFeBTa或CoHf可以位于CoFeB第一铁磁层和bcc NiFe插入层之间。bccNiFe插入层(以及可选的非晶分隔层，如果其被使用)防止fcc NiFe层在退火期间不利地影响MgO和CoFeB层的(001)晶体形成。bcc NiFe插入层还增大TMR并降低自由铁磁多层的Gilbert阻尼常数；然而，自由层磁致伸缩会增加。
为了更全面理解本发明的本质和优点，应当参照以下结合附图的详细描述。
附图说明
图1是示出常规隧穿磁阻(TMR)读头的结构的示意性截面图。
图2是示出现有技术的TMR读头的具体结构的示意性截面图。
图3是示出现有技术的TMR读头中的典型的参考层/MgO/自由层结构的示意性截面图。
图4是示出根据本发明的实施方式的具有体心立方(bcc)NiFe合金插入层的TMR读头中的参考层/MgO/自由层结构的示意性截面图。
图5是比较根据本发明的实施方式的结构与没有bcc NiFe插入层但具有各种非晶分隔层的结构的Gilbert阻尼常数的柱状图。
具体实施方式
图2是高度示意的截面图，示出如用于磁记录盘驱动器的现有技术的TMR读头100的结构。此截面图是通常被称为TMR读头100的空气轴承表面(ABS)的视图。TMR读头100包括形成在通常由电镀NiFe合金膜制成的两个铁磁屏蔽层S1、S2之间的传感器叠层。下屏蔽S1通常通过化学机械抛光(CMP)而平滑化，以提供用于生长传感器叠层的光滑表面。传感器叠层包括：铁磁参考层120，具有横向地取向(远离纸面)的被钉扎的磁化121；铁磁自由层110，具有能够响应于来自记录磁盘的横向外部磁场而在层110的平面中旋转的磁化111；以及在铁磁参考层120和铁磁自由层110之间的电绝缘隧穿势垒层130，通常是氧化镁(MgO)。在静止状态，即没有从记录磁盘施加的磁场，自由层110的磁化111正交于参考层120的磁化121取向。
参考层120可以是常规的“简单的”或单个的被钉扎层，其磁化方向121通常通过交换耦合到反铁磁层而被钉扎或者被固定。然而，在图2的示例中，参考层120是公知的反平行(AP)被钉扎结构或者磁通闭合结构的一部分，也被称为“层叠”被钉扎层，如美国专利5465185中描述的。AP被钉扎结构最小化参考层120与自由层110的静磁耦合。AP被钉扎结构包括跨过诸如Ru、Ir、Rh或Cr或者其合金的AP耦合(APC)层123而反铁磁耦合的参考铁磁(AP2)层120和下被钉扎铁磁(AP1)层122。由于跨过APC层123的反平行耦合，参考(AP2)铁磁层120和被钉扎(AP1)铁磁层122具有它们各自的彼此反平行取向的磁化121、127。结果，AP2铁磁层120和AP1铁磁层122的净磁化如此小以至于由铁磁自由层110中的磁通闭合结构导致的退磁场基本上被最小化，因此使得TMR读头最佳地运行变得可能。
籽层125和反铁磁(AF)钉扎层124位于下屏蔽层S1和AP被钉扎结构之间。籽层125促进AF钉扎层124生长具有强的晶体织构的微观结构，并因此产生强的反铁磁性。籽层125可以是单层或者不同材料的多层。AF钉扎层124因此强交换耦合到铁磁被钉扎层122，从而将铁磁被钉扎层122的磁化127牢固地钉扎在垂直于ABS并远离ABS的方向上。然后跨过APC层123的反平行耦合将铁磁参考层120的磁化121牢固地钉扎在垂直于ABS并朝向ABS的方向上并反平行于磁化127。结果，铁磁AP2层120和铁磁AP1层122的净磁化被牢固地钉扎，因此保证TMR读头的最佳运行。代替被AF层钉扎，AP1层122可以自身是硬磁层或者使其磁化127通过硬磁层诸如Co100-xPtx或者Co100-x-yPtxCry(其中x在约8和约30原子百分比之间)而被钉扎。AP被钉扎结构也可以“被自钉扎(self-pinned)”。在“被自钉扎”的传感器中，AP1层和AP2层的磁化方向127、121通常设定为通过存在于所制造的传感器中的残余应力和磁致伸缩而大致垂直于磁盘表面。
层112(有时被称为覆盖层或者盖层)位于铁磁自由层110和上屏蔽层S2之间。层112在加工期间保护铁磁自由层110免受化学和机械损伤，使得铁磁自由层110保持良好的铁磁性质。
在存在感兴趣的范围内的外部磁场(即，来自记录磁盘上的被写入数据的磁场)的情况下，虽然铁磁层120、122的净磁化保持被牢固地钉扎，但铁磁自由层110的磁化111将响应于磁场而旋转。因此，当感测电流IS从上屏蔽层S2经过传感器叠层垂直地流动到下屏蔽层S1时，铁磁自由层110的磁化旋转将导致铁磁参考层120的磁化和铁磁自由层110的磁化之间的角度的变化，这可检测为电阻的变化。由于感测电流被垂直地引导穿过两个屏蔽S1和S2之间的叠层，所以TMR读头100是电流垂直于平面(CPP)读头。
图2还示出可选的分别在屏蔽S1、S2与传感器叠层之间的单独的电引线(electrical leads)126、113。引线126、113可以由Ta、Ti、Ru、Rh或者其多层形成。引线是可选的并可以用于调节屏蔽至屏蔽的间隔。如果不存在引线126和113，则底部屏蔽S1和顶部屏蔽S2被用作电引线。铁磁参考层120和铁磁自由层110通常由CoFe、CoFeB或者NiFe层形成，或者由包括这些膜的多个层形成，而铁磁被钉扎层122通常由CoFe合金形成。籽层125通常由包括Ta/NiFeCr/NiFe、Ta/NiFe、Ta/Ru或者Ta/Cu膜的多个层形成。AFM钉扎层124通常由FeMn、NiMn、PtMn、IrMn、PdMn、PtPdMn或者RhMn膜制成。盖层112通常由Ru、Rh、Ti、Ta或者其多层制成。
虽然图2所示的TMR读头100是“底部被钉扎”的读头，因为AP被钉扎结构在自由层110下面，但是自由层110可以位于AP被钉扎结构下面。在这样的布置中，AP被钉扎结构的各层被颠倒，使AP2层120在势垒层130顶上并接触势垒层130。
MgO隧道结要求具有(001)外延和理想的结晶度。MgO势垒层通常通过溅射沉积和随后的退火(其形成晶体结构)而形成。已经发现，在参考层和自由层中的一个或两者中使用薄的非晶CoFeB导致较高的隧穿磁阻(ΔR/R或者TMR)。已知刚沉积的(as-deposited)非晶CoFeB层促进MgO在(001)方向的高质量结晶，因此在退火之后实现更高的TMR。因此图3示意地示出根据现有技术的典型的参考层/MgO/自由层结构。参考层/MgO/自由层结构被示出为位于常规屏蔽S1和S2之间，并且常规的反铁磁(AF)层和籽层在参考层下面且常规的覆盖层在自由层上面。参考层和自由层的每个的总厚度通常在约和之间。自由铁磁层被描绘为以下的多层：与MgO势垒层相邻的薄的(例如在约厚度之间)可选的CoFe“纳米层”、具有约之间的厚度的CoFeB层、具有约之间的厚度的基本上面心立方(fcc)NiFe层、以及在CoFeB层和fcc NiFe层之间的具有约之间的厚度的可选的非晶分隔层(例如，Ta、Zr、Hf、CoHf或者CoFeBTa层)。CoFe纳米层和CoFeB层具有正磁致伸缩；然而，fcc NiFe层具有负磁致伸缩并可以因此被认为是补偿正磁致伸缩的补偿层。fccNiFe补偿层具有基本上fcc晶体结构。因为fcc NiFe层在退火之后会不利地影响MgO势垒与CoFe纳米层和CoFeB层之间的外延关系，并因此降低TMR，所以非晶分隔层可以用于使fccNiFe层与CoFe纳米层和CoFeB层分隔。
在本发明的实施方式中，基本上体心立方(bcc)的NiFe插入层位于fcc NiFe补偿层和CoFeB层(或者可选的非晶分隔层，如果使用的话)之间。bcc NiFe插入层具有基本上bcc晶体结构。通常bcc NiFe具有大于或等于40at.％的Fe组分。与fcc NiFe补偿层的通常小于或等于15at.％的Fe含量相比，bcc NiFe层具有相对高的Fe含量(等于或者大于40at.％)。bcc NiFe插入层降低Gilbert阻尼常数并且还改善MR比，但是磁致伸缩也增加。
一实施方式在图4的截面图中绘出。参考层/MgO/自由层结构被示出为位于常规屏蔽S1和S2之间，并且常规的反铁磁(AF)层和籽层在参考层下面，常规的覆盖层在自由层上面。参考层可以由CoFe、CoFeB或者NiFe层(或者这些材料的多层)形成并可以是简单的被钉扎参考层或者AP被钉扎结构的AP2层，这两者都在以上结合图2而描述。MgO隧穿势垒层具有在约之间的典型厚度。可选的CoFe合金纳米层具有在约20至80at.％之间的Fe含量以及在约之间的厚度。Co或Fe纳米层可以被用作CoFe纳米层的替代。CoFeB合金层具有(CoxFe(100-x))(100-y)By的典型组分，其中下标表示at.％，x等于或者大于60并且小于100，y在约10与20之间。可选的分隔层可以是非晶Ta、Zr、Hf或者CoFeBTa合金层，或者是具有在约之间的厚度并且Hf含量在约10-30at.％之间的非晶CoHf合金层。fcc NiFe层可以具有在约之间的厚度以及在约2-15at.％之间的低的Fe含量。在本发明的实施方式中，bcc NiFe层具有在约之间的厚度并且Fe含量大于或等于40at.％，优选地在约40-55at.％之间。
以上描述的并且在图4中示出的TMR读头通过以溅射沉积或者其他已知的薄膜沉积技术沉积传感器叠层中的层而以常规方式制造。然后在存在施加磁场的情况下该结构被退火以设定参考铁磁层的磁化的方向。退火通常在约250至290℃进行约4至24小时。退火还形成具有期望的结晶度的MgO势垒层。bcc NiFe插入层(以及可选的分隔层，如果使用的话)防止fcc NiFe层不利地影响MgO层和CoFeB层的(001)晶体形成。在沉积并退火这些膜之后，叠层被光刻图案化(lithographically patterned)和蚀刻以限定读头的期望尺寸。
还发现bcc NiFe层增大TMR。对于如图4所示的具有非晶分隔层和bcc NiFe插入层的结构，发现TMR的提高在2-10％之间。
还发现bcc NiFe层降低了Gilbert阻尼常数。这在图5的柱状图中示出，图5比较了如图4所示的具有各种bcc NiFe插入层的结构与没有bcc NiFe插入层而只有各种非晶分隔层(CoFeBTa和CoHf)的结构。具有bcc NiFe插入层的结构表现出约0.012的阻尼常数，而仅具有非晶分隔层的结构表现出从约0.015至0.025的阻尼常数。尤其值得注意的是，仅具有CoHf分隔层的结构表现出约0.024的阻尼常数。当bcc NiFe插入层被添加到该结构时，阻尼常数显著地减小到0.012。
虽然已经参照优选的实施方式具体示出和描述了本发明，但是本领域技术人员将理解，可以在其中进行形式和细节上的各种改变而没有脱离本发明的精神和范围。因此，所公开的发明将仅被认为是说明性的并且被限制在仅如权利要求书所指定的范围内。

Claims (20)

1.一种隧穿磁阻(TMR)器件，包括：
基板；
参考铁磁层，在所述基板上；
隧穿势垒层，在所述参考铁磁层上并由MgO构成；和
自由铁磁多层，包括在所述隧穿势垒层上的第一铁磁层、具有负磁致伸缩的第二铁磁层、以及在所述自由多层的所述第一铁磁层和所述第二铁磁层之间的具有体心立方(bcc)晶体结构的镍铁(NiFe)合金铁磁插入层。
2.如权利要求1所述的器件，其中所述自由铁磁多层的所述第二铁磁层是具有面心立方(fcc)晶体结构的NiFe合金层。
3.如权利要求2所述的器件，其中所述fcc NiFe合金层包含小于或等于15原子百分比的量的Fe。
4.如权利要求1所述的器件，其中所述铁磁插入层包含大于或等于40原子百分比的量的Fe。
5.如权利要求4所述的器件，其中所述铁磁插入层包含大于或等于40原子百分比且小于或等于55原子百分比的量的Fe。
6.如权利要求1所述的器件，其中所述自由铁磁多层的所述第一铁磁层是CoFeB合金层。
7.如权利要求1所述的器件，还包括在所述势垒层和所述第一铁磁层之间并从Co、Fe以及Co和Fe组成的合金中选择的铁磁纳米层。
8.如权利要求1所述的器件，还包括在所述自由铁磁多层的所述第一铁磁层与所述铁磁插入层之间的非晶分隔层。
9.如权利要求8所述的器件，其中所述非晶分隔层从Ta、Zr、Hf、CoFeBTa合金和CoHf合金中选择。
10.如权利要求1所述的器件，其中所述参考层是反平行(AP)被钉扎结构的一部分，所述反平行被钉扎结构包括：具有平面内磁化方向的第一反平行被钉扎(AP1)铁磁层、与所述隧穿势垒层相邻并具有反平行于所述第一反平行被钉扎层的所述磁化方向的平面内磁化方向的第二反平行被钉扎(AP2)铁磁层、以及在所述第一反平行被钉扎层和所述第二反平行被钉扎层之间并且与所述第一反平行被钉扎层和所述第二反平行被钉扎层接触的反平行耦合(APC)层，其中所述参考层是所述第二反平行被钉扎层。
11.如权利要求10所述的器件，还包括交换耦合到所述第一反平行被钉扎层的反铁磁层，该反铁磁层用于钉扎所述第一反平行被钉扎层的磁化方向。
12.一种隧穿磁阻(TMR)读头，包括：
导磁材料的第一屏蔽层；
参考铁磁层，在所述第一屏蔽层上并具有被防止在存在外部磁场的情况下旋转的平面内磁化方向；
由MgO构成的电绝缘隧穿势垒层，在所述参考层上并接触所述参考层；
自由铁磁多层，在所述隧穿势垒层上并具有在没有外部磁场的情况下正交于所述参考层的磁化方向取向的平面内磁化方向，所述自由铁磁多层包括：在所述隧穿势垒层上的第一铁磁层、具有等于或小于15原子百分比的Fe含量的镍铁(NiFe)合金铁磁补偿层、以及在所述第一铁磁层和所述铁磁补偿层之间的具有等于或大于40原子百分比的Fe含量的NiFe合金铁磁插入层；
覆盖层，在所述自由铁磁多层上；以及
在所述覆盖层上的导磁材料的第二屏蔽层。
13.如权利要求12所述的读头，其中所述NiFe合金补偿层具有面心立方(fcc)晶体结构，并且所述NiFe合金插入层具有体心立方(bcc)晶体结构。
14.如权利要求12所述的读头，其中所述自由铁磁多层的所述第一铁磁层是CoFeB合金层。
15.如权利要求12所述的读头，还包括在所述势垒层和所述第一铁磁层之间并从Co、Fe以及Co和Fe组成的合金中选择的铁磁纳米层。
16.如权利要求12所述的读头，还包括在所述自由铁磁多层的所述第一铁磁层与所述NiFe合金插入层之间的由Co和Hf构成的分隔层。
17.如权利要求12所述的读头，还包括：
反平行(AP)被钉扎结构，在所述第一屏蔽层和所述势垒层之间并包括：第一反平行被钉扎(AP1)铁磁层，在所述第一屏蔽层上并具有平面内磁化方向；第二反平行被钉扎(AP2)铁磁层，具有反平行于所述第一反平行被钉扎层的磁化方向的平面内磁化方向；以及反平行耦合(APC)层，在所述第一反平行被钉扎层和所述第二反平行被钉扎层之间并且与所述第一反平行被钉扎层和所述第二反平行被钉扎层接触，其中所述参考层是所述第二反平行被钉扎层；以及
反铁磁层，交换耦合到所述第一反平行被钉扎层用于钉扎所述第一反平行被钉扎层的磁化方向。
18.一种隧穿磁阻(TMR)读头，包括：
导磁材料的第一屏蔽层；
参考铁磁层，在所述第一屏蔽层上并具有被防止在存在外部磁场的情况下旋转的平面内磁化方向；
由MgO构成的电绝缘隧穿势垒层，在所述参考层上并接触所述参考层；
自由铁磁多层，在所述隧穿势垒层上并具有在没有外部磁场的情况下正交于所述参考层的磁化方向取向的平面内磁化方向，所述自由铁磁多层包括：
在所述MgO势垒层上的CoFe合金纳米层，具有等于或大于20原子百分比并且等于或小于80原子百分比的Fe含量；
CoFeB合金铁磁层，在所述CoFe合金纳米层上；
在所述CoFeB合金层上的非晶分隔层，从Ta、Zr、Hf、CoFeBTa合金和CoHf合金中选择；
NiFe合金铁磁补偿层，具有等于或小于15原子百分比的Fe含量；以及
NiFe合金铁磁插入层，在所述分隔层和所述NiFe合金补偿层之间，具有等于或大于40原子百分比并且小于或等于55原子百分比的Fe含量；
覆盖层，在所述自由铁磁多层上；以及
在所述覆盖层上的导磁材料的第二屏蔽层。
19.如权利要求18所述的读头，其中所述NiFe合金补偿层具有面心立方(fcc)晶体结构，并且所述NiFe合金插入层具有体心立方(bcc)晶体结构。
20.如权利要求18所述的读头，还包括：
反平行(AP)被钉扎结构，在所述第一屏蔽层和所述势垒层之间并包括：第一反平行被钉扎(AP1)铁磁层，在所述第一屏蔽层上并具有平面内磁化方向；第二反平行被钉扎(AP2)铁磁层，具有反平行于所述第一反平行被钉扎层的磁化方向的平面内磁化方向；以及反平行耦合(APC)层，在所述第一反平行被钉扎层和所述第二反平行被钉扎层之间并且与所述第一反平行被钉扎层和所述第二反平行被钉扎层接触，其中所述参考层是所述第二反平行被钉扎层；以及
反铁磁层，交换耦合到所述第一反平行被钉扎层用于钉扎所述第一反平行被钉扎层的磁化方向。
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