Large inverse magnetoresistance of CrO 2 ∕ Co junctions with an artificial barrier
Large inverse magnetoresistance of CrO 2 ∕ Co junctions with an artificial barrier
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DOI：
10.1103/physrevb.69.220413
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发表时间：
2004-06
影响因子：
3.7
通讯作者：
Jeffrey Stuart Parker;P. G. Ivanov;D. Lind;P. Xiong;Y. Xin
中科院分区：
文献类型：
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作者：
Jeffrey Stuart Parker;P. G. Ivanov;D. Lind;P. Xiong;Y. Xin
近年来，电子的电荷和自旋都起着重要作用的器件引起了人们的极大兴趣。一种这样的器件由由绝缘屏障隔开的两个铁磁(FM)层组成，该绝缘屏障通常被称为磁隧道结(MTJ)。这种结构的两个电极主要由过渡金属铁磁体制成。各种MTJ在低场下表现出大的隧道磁阻(TMR)效应：1当两个铁磁电极的磁化强度从平行转变为反平行时，结电阻发生急剧变化。这种效应有望将MTJ用作敏感的磁场传感器和非易失性磁性随机存取存储器。2理想MTJ的结磁电阻(JMR)只与电极的电子态密度(DOS)和自旋极化P有关，并且JMR的大小和符号通过一个简单的方程与电极的P有关。最近的研究表明，即使在通过势垒的跳跃传输而不是直接隧道传输的情况下，也可以获得实质性的JMR。JMR被理解为在势垒中通过局域态的自旋守恒跳跃，并被用来推断电极的P的大小和符号。迄今报道的金属基MTJ在室温下的最大磁阻(MR)约为40%，5，6，与常见铁磁金属的典型P值S30%-50%d一致。从材料的角度来看，提高JMR的下一步显然是用具有更高自旋极化的材料来制造MTJ。有一类材料引起了特别的兴趣，那就是所谓的半金属。在半金属中，两个自旋物种具有不同的能级密度：费米能级位于一个自旋能带内，而另一个自旋能带有一个能隙，因此巡回载流子是100%自旋极化的。具有全半金属电极SP1=P2=1d的MTJ将产生
Devices in which both the charge and spin of electrons play important roles have generated substantial interest in recent years. One such device consists of two ferromagnetic (FM) layers separated by an insulating barrier, typically referred to as a magnetic tunnel junction (MTJ). The two electrodes of such structures are mostly made of transition-metal ferromagnets. Various MTJ’s have exhibited large tunneling magnetoresistance (TMR) effects at low fields: 1 the junction resistance changes abruptly and substantially when the magnetization of the two ferromagnetic electrodes switches from parallel to antiparallel. Such effect promises applications for MTJ’s as sensitive magnetic-field sensors and in nonvolatile magnetic random access memory. 2 The junction magnetoresistance (JMR) of an ideal MTJ depends only on the electronic density of states (DOS) and spin polarization, P ,o f the electrodes described by a model proposed by Julliere, 3 and the magnitude and sign of the JMR are related to P of the electrodes through a simple equation. Recently, it was shown 4 that substantial JMR can be obtained even in the case of hopping transport through the barrier instead of direct tunneling. The JMR was understood with spin conserving hopping through localized states in the barrier and was used to infer the magnitude and sign of P of the electrode. The maximum magnetoresistance (MR) reported to date of metalbased MTJ’s at room temperature is found to be around 40%, 5,6 consistent with typical P values s30% ‐ 50%d of the common ferromagnetic metals. From a materials standpoint, an obvious next step to enhance the JMR is to fabricate MTJ’s from materials with higher spin polarization. One class of materials that has attracted particular interest is the so-called half metals. In a half metal the two spin species have different DOS: the Fermi level lies within one spin band, while the other spin band has a gap, thus the itinerant charge carriers are 100% spin polarized. An MTJ with all half-metallic electrodes sP1 = P2 =1 d would produce