Demonstration of high-frequency oscillation in a Co-based Heusler alloy tunnel junction

关键词：半金属，Heusler合金，MRAM， Gilbert阻尼和交换偏置建立了一种可复制的制造磁性隧道结（MTJ）的工艺，该结由MgO势垒夹在外延Co2FeAl0.5Si0.5薄膜电极中组成。2 .室温下非常大隧穿磁阻（TMR）比的证明。基于小吉尔伯特阻尼常数和大自旋极化的高效电流感应磁化开关（CIMS）的演示。首次制备了Co2FeAl0.5Si0.5结的高频自旋振荡原型。方法:1。利用超高真空（UHV）溅射/分子束外延（MBE）生长和NIMS的纳米制造，结合约克大学最先进的扫描透射电子显微镜（STEM）进行界面原子分析。基于上述反馈工艺，制备了高质量的Co2FeAl0.5Si0.5/MgO/Co2FeAl0.5Si0.5结。3 .在NIMS[平面隧道电流分析和温度相关TMR测量]和York[振动样品磁强计（VSM）和磁光克尔效应（MOKE）]的高灵敏度磁化分析。基于赫斯勒纳米柱的CIMS的高频工作和共面波导的电检测。预期结果：1；揭示Co2FeAl0.5Si0.5/MgO界面原子结构与弹道自旋极化电子隧穿特性之间的关系。改进了世界纪录的TMR比（室温下386%，9k下832%）及其温度依赖关系，以遵循磁化的经验温度依赖关系。临界电流密度降低到106 a /cm24以下。Co2FeAl0.5Si0.5薄膜阻尼常数的估计。为了实现未来自旋随机存取存储器的应用，最近对一种在室温下具有100%自旋极化的新型铁磁材料进行了深入的研究。我们将采用Co2FeAl0.5Si0.5 Heusler合金薄膜，它具有最高的自旋极化，在室温下产生迄今为止最大的隧穿磁阻。Heusler薄膜的磁隧道结将通过超高真空溅射和分子束外延在NIMS上外延生长，然后将在约克用最先进的电子显微镜和磁强计进行表征。通过改善薄膜的界面原子结构来对抗MgO隧道势垒，将证明更高的TMR比。高频测量也将进行，以确定其阻尼常数，这将比传统的铁磁体小。这些结有望在~100%的自旋极化和非常小的阻尼常数方面具有显着的优势，从而实现自旋存储器中快速有效的开关。在这个项目的最后，我们将首次尝试用Heusler合金薄膜制造一个高频振荡器的原型。

Keywords: half-metals, Heusler alloys, MRAM, Gilbert damping and exchange biasGoals: 1. Establishment of a reproducible process to fabricate a magnetic tunnel junction (MTJ), consisting of a MgO barrier sandwiched with epitaxial Co2FeAl0.5Si0.5 film electrodes.2. Demonstration of very large tunnelling magnetoresistance (TMR) ratio at room temperature (RT).3. Demonstration of efficient current-induced magnetisation switching (CIMS) based on a small Gilbert damping constant and large spin polarisation.4. Nanofabrication of a prototype of a high-frequency spin oscillation with the Co2FeAl0.5Si0.5 junction for the first time.Approach: 1. Device fabrication using ultrahigh vacuum (UHV) sputtering/molecular beam epitaxy (MBE) growth and nanofabrication at NIMS combined with interfacial atomic analysis by state-of-the-art scanning transmission electron microscopy (STEM) at York.2. Based on the above feedback process, nanopillar fabrication of high-quality Co2FeAl0.5Si0.5/MgO/Co2FeAl0.5Si0.5 junctions.3. Highly sensitive magnetisation analysis both at NIMS [current in plane tunnelling analysis and temperature-dependent TMR measuremsnts] and York [vibrating sample magnetometer (VSM) and magneto-optical Kerr effect (MOKE)].4. High-frequency operation of the CIMS in a Heusler-based nanopillar and electrical detection by coplanar waveguide.Expected outcome: 1. To reveal a correlation between atomic structures at the Co2FeAl0.5Si0.5/MgO interfaces and ballistic spin-polarised electron tunnelling properties.2. Improvement of the world-record TMR ratio (386% at RT and 832% at 9 K) and its temperature dependence to follow the empirical temperature dependence of magnetisation.3. Decrease of a critical current density below 106 A/cm24. Estimation of a damping constant of the Co2FeAl0.5Si0.5 film.An intensive search for a new ferromagnetic material with 100% spin polarisation at room temperature has been carried out recently for the realisation of a future spin random access memory application. We will employ Co2FeAl0.5Si0.5 Heusler alloy films, which hold the highest spin polarisation, resulting the largest tunnelling magnetoresistance at room temperature to date. Magnetic tunnel junctions with the Heusler films will be epitaxially grown at the NIMS by ultrahigh vacuum sputtering and molecular-beam epitaxy, and will then be characterised at York with the state-of-the-art electron microscopy and magnetometry. By improving the interfacial atomic structures of the films against a MgO tunnel barrier, larger TMR ratios will be demonstrated. High-frequency measurements will also be performed to define their damping constants, which are to be smaller than the conventional ferromagnets. These junctions are expected to take significant advantages in both ~100% spin polarisation and a very small damping constant for the realisation of fast and efficient switching in a spin memory. At the end of this project, we will attempt to fabricate a prototype of a high-frequency oscillator with Heusler alloy films for the first time.