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首页> 外文期刊>Physical review. B, Condensed Matter And Materials Physics >Influence of oxygen on the interfacial stability of Cu on Co(0001) thin films
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Influence of oxygen on the interfacial stability of Cu on Co(0001) thin films

机译：氧对Co（0001）薄膜上Cu界面稳定性的影响

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摘要

Vapor deposited Cu/Co multilayers with high quality Co-Cu interfaces exhibit significant giant magnetore-sistance. These multilayers are sometimes grown using process environments with significant background partial pressures of oxygen, which can impact the quality of film and its properties. Previously we found that oxygen preferentially stabilizes Co/Cu(111). First principle density functional theoretical calculations are used herein to examine the effects of surface atomic oxygen on the stability of the Cu(111)/Co(0001) interface. This interface can be grown with varying degrees of intermixing at the surface. We examine the significance of this by analyzing the first two Cu layers deposited on a Co(0001) substrate. The effects of oxygen are studied for the nonmixed Cu_(1 ML)/Co_(1 ML)/Co(0001) system, the mixed Co_(0.33)Cu_(0.67)/Co_(0.67)Cu_(0.33)/Co(0001) and Co_(0.66)Cu_(0.33)/Co_(0.33)Cu_(0.67)/Co(0001) surface alloys and the Co-capped Co_(1 ML)/Cu_(1 ML)/Co(0001) system. In the absence of oxygen, the nonmixed Cu_(1 ML)/CO_(1 ML)/Co(0001) system is found to be the most stable. The calculations show that the fraction of the surface comprised of Cu, in the absence of background oxygen, is maximized for Cu deposited onto a Co(0001) substrate. This reduces the tendency for intermixing. Submono-layer coverages of atomic oxygen preferentially bind at the three-fold fcc and hcp sites on all four Cu/Co(0001) surfaces investigated as well as on the homogeneous Co(0001) and the Cu(111) surfaces. The difference in the oxygen-metal binding energy for the fee and hep sites appears to be negligible which is consistent with the minor changes that occur in the local structure (oxygen height above the surface and interlayer spacing). Total energy calculations indicate that the intermixing is unfavorable when the oxygen coverage is kept below 0.362 ML. This threshold coverage is hardly affected by the oxygen binding sites (hcp and fcc), stacking sequence of the metal layer or thicker Cu layers. This threshold oxygen coverage minimizes the influence of the surface oxygen on the magnetic properties of the system. These results, taken with other calculations for Co/Cu(111), suggest that 0.362 ML of oxygen is optimal for stabilizing the Co/Cu(111) interface without disrupting the stability of the Cu/Co(0001) interface. The calculations show that the addition of oxygen to the Cu-segregated unmixed CU_(1 ML)/Co_(1 ML)/Co(0001) surface increases the surface magnetization as a result of the unpaired electrons that arise from the surface oxygen atoms. The addition of atomic oxygen to the Co-capped Co_(1 ML)/Cu_(1 ML)/Co(0001) surface, on the other hand, results in an increase in the magnetization for oxygen coverages up to 0.33 ML. At higher oxygen coverages, however, there is a shifting of the minority states toward the majority states near the Fermi level which significantly reducing the magnetization of the surface Co layer.
机译：具有高质量Co-Cu界面的气相沉积Cu / Co多层膜表现出显着的巨磁阻。这些多层有时是在具有显着背景氧分压的工艺环境下生长的，这会影响薄膜的质量及其性能。以前我们发现氧优先稳定Co / Cu（111）。第一原理密度泛函理论计算在本文中用于检查表面原子氧对Cu（111）/ Co（0001）界面稳定性的影响。该界面可以在表面以不同程度的混合程度生长。我们通过分析沉积在Co（0001）衬底上的前两个Cu层来检验其重要性。研究了非混合Cu_（1 ML）/ Co_（1 ML）/ Co（0001）系统，混合Co_（0.33）Cu_（0.67）/ Co_（0.67）Cu_（0.33）/ Co（0001）对氧气的影响）和Co_（0.66）Cu_（0.33）/ Co_（0.33）Cu_（0.67）/ Co（0001）表面合金以及Co-封端的Co_（1 ML）/ Cu_（1 ML）/ Co（0001）系统。在没有氧气的情况下，发现非混合的Cu_（1 ML）/ CO_（1 ML）/ Co（0001）系统是最稳定的。计算表明，在没有背景氧的情况下，由Cu构成的表面分数对于沉积在Co（0001）衬底上的Cu而言是最大的。这减少了混合的趋势。原子氧的亚单层覆盖优先结合在所有研究的四个Cu / Co（0001）表面以及均质Co（0001）和Cu（111）表面的三倍fcc和hcp位置。费位和大麻位的氧-金属结合能差异似乎可以忽略不计，这与局部结构中发生的细微变化（表面上方的氧高度和中间层间距）一致。总能量计算表明，当氧气覆盖率保持在0.362 ML以下时，混合是不利的。此阈值覆盖率几乎不受氧结合位点（hcp和fcc），金属层或较厚的Cu层堆叠顺序的影响。该阈值氧覆盖率使表面氧对系统磁性能的影响最小化。这些结果以及其他针对Co / Cu（111）的计算得出的结果表明，0.362 ML的氧气最适合用于稳定Co / Cu（111）界面而不会破坏Cu / Co（0001）界面的稳定性。计算表明，由于表面氧原子产生的不成对电子，向铜分离的未混合CU_（1 ML）/ Co_（1 ML）/ Co（0001）表面添加氧会增加表面磁化强度。另一方面，向共封顶的Co_（1 ML）/ Cu_（1 ML）/ Co（0001）表面添加原子氧会导致氧覆盖的磁化强度增加至0.33 ML。然而，在较高的氧气覆盖率下，少数状态向费米能级附近的多数状态移动，这大大降低了表面Co层的磁化强度。

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