Spin-dependent tunnelling characteristics of fully epitaxial magnetic tunnel junctions with a Heusler alloy Co2MnGe thin film and a MgO barrier
Spin-dependent tunnelling characteristics of fully epitaxial magnetic tunnel junctions with a Heusler alloy Co2MnGe thin film and a MgO barrier
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DOI：
10.1088/0022-3727/42/8/084015
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发表时间：
2009-04
期刊：
影响因子：
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通讯作者：
T. Taira;T. Ishikawa;Naoki Itabashi;K. Matsuda;T. Uemura;Masafumi Yamamoto
中科院分区：
文献类型：
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作者：
T. Taira;T. Ishikawa;Naoki Itabashi;K. Matsuda;T. Uemura;Masafumi Yamamoto
我们研究了由Heusler合金Co2 MnGe（CMG）下电极、MgO阻挡层和Co 50 Fe 50上电极组成的全外延磁性隧道结（MTJ）的自旋相关隧穿特性，这些磁性隧道结是作为Ta的函数制造的，其中Ta是MTJ三层在沉积上电极后立即原位退火的温度。我们发现，当Ta从475 ° C增加到500 °C时，隧道磁阻（TMR）比从室温（RT）的92%（4.2K时为244%）不连续地显著增加到RT的160%（4.2K时为376%）。我们还发现，对于平行（P）和反平行（AP）磁化配置，所制造的MTJ的dI/dV对V特性随着Ta从475 °C或更低增加到500 °C或更高而不连续地且显著地改变;即dI/Ta为475 °C或更低的MTJ的dV-V特性在V = 0.22 V（P）和V =-0.38和0.27 V（AP）处表现出明显的峰值结构，其中相对于CMG下电极定义偏置电压（V）。另一方面，当Ta为500 °C或更高时，在MTJ的dI/dV对V特性中未观察到这些结构。我们将dI/dV对V特性中的峰结构归因于CMG电极-MgO势垒界面处的界面态密度中的峰结构的存在，所述界面态密度中的峰结构由具有475 °C或更低的Ta的CMG/MgO/Co 50 Fe 50 MTJ中可能的热稳定界面键合引起。dV对V特性的变化与界面键合从Ta为475 °C或更低时的热稳定键合到Ta为500 °C或更高时的稳定键合的变化有关。随着Ta从475 ° C增加到500 °C，TMR比率的显著增加归因于与自旋相关的界面态密度的变化相关的费米能级处的界面自旋极化的增加。
We investigated the spin-dependent tunnelling characteristics of fully epitaxial magnetic tunnel junctions (MTJs) consisting of a Heusler alloy Co2MnGe (CMG) lower electrode, a MgO barrier and a Co50Fe50 upper electrode, which were fabricated as a function of Ta, where Ta is the temperature at which the MTJ trilayer was in situ annealed right after deposition of the upper electrode. We found that the tunnel magnetoresistance (TMR) ratio increased discontinuously and significantly from 92% at room temperature (RT) (244% at 4.2 K) to 160% at RT (376% at 4.2 K) when Ta was increased from 475 to 500 °C. We also found that the dI/dV versus V characteristics of fabricated MTJs for the parallel (P) and antiparallel (AP) magnetization configurations changed discontinuously and markedly with increasing Ta from 475 °C or less to 500 °C or higher; i.e. the dI/dV versus V characteristics of the MTJs with Ta of 475 °C or less exhibited distinct peak structures at V ∼ 0.22 V for P and at V ∼ −0.38 and 0.27 V for AP, where the bias voltage (V) was defined with respect to the CMG lower electrode. On the other hand, these structures were not observed in the dI/dV versus V characteristics of the MTJs when Ta was 500 °C or higher. We ascribe the peak structures in the dI/dV versus V characteristics to the existence of peak structures in the interfacial density of states at the CMG electrode–MgO barrier interface arising from possible thermodynamically unstable interface bonding in CMG/MgO/Co50Fe50 MTJs with Ta of 475 °C or less. We attribute the discontinuous and complete disappearance of these peaks in the dI/dV versus V characteristics to the change in the interface bonding from thermodynamically unstable bonding for Ta of 475 °C or less to stable bonding for Ta of 500 °C or higher. The significant increase in the TMR ratio with increasing Ta from 475 to 500 °C is attributed to the increase in the interfacial spin polarization at the Fermi level associated with the change in the spin-dependent interfacial density of states.