Development of Magnetoresistive Halfmetals and Halfmetallic Composites for Spintronics

我们为期三年的项目专注于半金属（HM）氧化物材料，该材料具有100%自旋极化载流子的铁磁体导电（在理想情况下）。这些材料构成了隧道型磁电阻（TMR）器件的基础，其应用在当前新兴的自旋电子学新技术中。在迄今为止发现的少数HM材料中，b位有序双钙钛矿（DP）氧化物A_2B'B' O_6，包括原型Sr_2FeMoO_6化合物是最有希望应用于室温（RT）低场（LF）的候选者。虽然相关的钙钛矿衍生体系也被研究了，但b位点有序的DPs在本项目中也起着中心作用。该项目的目标是通过控制其内在和外在的材料特性来寻找这些材料作为RT-LF-TMR材料的极限。研究内容包括以下几个方面：(1)Sr_2FeMoO_6和相关DP氧化物的原子级固有特性裁剪(2)通过选择合成条件控制晶粒/磁畴尺寸(3)复合结构设计以增强RT-LF TMR特性(4)在钙钛矿氧化物中寻找新的HM化合物(s)我们独特的（新）材料设计和裁剪方案本身。包括原子到宏观的各种内在和外在的材料参数的操作，被证明是非常成功的。我们积极地相信，我们的方法在未来也会被发现是有用的，可以为广泛的前沿材料实现更有组织和高效的设计方案。

Our three-year project was focused on halfmetallic (HM) oxide materials that are conducting ferromagnets with 100 % spin-polarized carriers (in an ideal case). Such materials form the bases for tunneling-type magnetoresistance (TMR) devices application of which is found in the presently emerging new technology called spintronics. Among the handful of HM materials discovered so far, B-site ordered double-perovskite (DP) oxides, A_2B'B''O_6, including the prototype Sr_2FeMoO_6 compound are the most promising candidates for room-temperature (RT) low-field (LF) application. The B-site ordered DPs were also in the central role in the present project, though related perovskite-derived systems were investigated as well. The goal of the project was to search for the limits of these materials to function as RT-LF-TMR materials by means of controlling their intrinsic and extrinsic material characteristics. The research included the following aspects:(i) Tailoring of atomic-level intrinsic characteristics of Sr_2FeMoO_6 and related DP oxides(ii) Control of the size of grains/magnetic domains by the choice of synthesis conditions(iii) Design of composite structures to enhance the RT-LF TMR characteristics(iv) Search for novel HM compound(s) among perovskite oxidesOur unique (new) material design and tailoring scheme itself, comprising atomic-to-macroscopic dimensional manipulation of various intrinsic and extrinsic material parameters, turned out to be highly successful. We positively believe that our approach will be found useful in future too to achieve a more organized and highly productive design scheme for a wide range of frontier materials.