超大各向异性磁电阻效应调控与机理研究

Magnetic sensors based on anisotropic magnetoresistance effect (AMR) has widely used in the IT field due to their some advantages, such as a simple preparation and low cost. Compared to the giant magnetoresistance effect (GMR), the AMR value in conventional ferromagnetic materials is small, resulting in the sensitivity of AMR devices is usually inferior to that of GMR devices. In perovskite manganites, we found a colossal AMR effect, which is two orders of magnitude larger than the conventional AMR effect. It is expected the devices base on the colossal AMR effects will indicate high sensitivity. However, the colossal AMR effect has not yet been obtained at room temperature and under a low magnetic field, and also the physical mechanism and modulation methods of the colossal AMR effect remain unclear so far. In this project, we select orbital/charge ordered manganites to investigate the relevance between the colossal AMR effect and the metal-insulator transition，orbital/charge/spin ordering transition，and phase separation. We will try to modulate the colossal AMR effects in critical conditions by a magnetic field,electric field, size/dimensionality effects,and also stress/strain effects, and then clarify the key factor determining the value, working temperature and magnetic field sensitivity of the colossal AMR, eventually find out the room-temperature colossal AMR materials and pave a new way for developing novel AMR devices.

基于各向异性磁电阻效应（AMR）的磁性传感器具有制备工艺简单、成本低等优点，在信息技术领域得到广泛应用。与巨磁电阻效应（GMR）相比，传统铁磁性材料中的AMR数值较小，导致AMR器件的灵敏度低于GMR器件。我们在钙钛矿型锰氧化物中发现了超大的AMR效应，比传统的AMR效应的数值大两个数量级。超大AMR材料的利用将会弥补传统AMR器件灵敏度偏低的缺点。但目前人们还没有在室温低磁场下获得超大的AMR效应，对超大AMR效应的物理机制及其调控方法尚不清楚。本项目选择电荷轨道有序的锰氧化物作为研究重点，研究超大AMR效应与金属-绝缘体转变、自旋/电荷轨道序转变、以及与相分离的内在关联规律与机制，在临界条件下研究磁场、电场、尺度/维度、以及应力等因素对超大AMR效应的调控规律，找出影响超大AMR数值、工作温度以及磁场灵敏度的关键因素，获得室温下可用的超大AMR材料，为研发下一代AMR器件奠定基础。

近年来发现，在钙钛矿锰氧化物中即便弱的晶体学各向异性也可以诱发出超大的各向异性磁电阻（CAMR）效应，这种效应表现出与过渡金属截然不同的磁场和温度依赖关系，说明其CAMR效应可能具有不同于传统3d磁性金属的物理起源。为了澄清钙钛矿锰氧化物中CAMR效应产生的机理，我们选取了一系列具有不同电子结构的锰氧化物材料体系，研究其CAMR效应与电子结构相变的关系。研究结果发现，在电荷轨道有序态体系中，无论系统处于顺磁态还是反铁磁态，轨道有序态在外加磁场下的破坏是产生CAMR效应的主要原因；而在电荷轨道无序的系统中，电子相分离是产生CAMR效应的重要条件。外加应力和掺杂通过影响锰氧化物薄膜的电子相分离温区和轨道结构，从而调控CAMR效应产生的温度区间、数值大小和角度依赖关系等。我们的研究结果表明，产生室温下受磁场调控的电子相分离结构是获得室温CAMR效应的重要手段。本项目的研究结果为探索室温下具有大的AMR效应的材料体系提供思路。