Electrical control of magnetism in oxide films and devices

通向新一代快速、低功率电子产品的最有希望的途径之一是绝缘体中的磁性的电气控制。这种方法利用了通过施加较小的写入电压来切换几类氧化物中的反铁磁状态的能力。然后，可以通过界面将自旋极化转移到铁磁材料，然后以常规方式读取，例如使用硬盘读取头中的隧道磁阻结。该方案可以用来制造快速、高效的非易失性存储器，而不需要写入电流来产生焦耳发热，从而消耗能量。我们最近开发了一套在外延氧化物薄膜和器件中同时成像反铁磁/铁磁畴及其电开关的技术。我们使用同步加速器X射线衍射和显微镜、内部磁力显微镜(MFM)和中子衍射的组合，使我们能够访问从1厘米到&lt；100 nm的长度尺度上的磁区。在过去的两年里，我们在麦迪逊大学的合作者生长的BiFeO_3薄膜和器件方面取得了一些非常令人兴奋的结果。在最近的实验中，我们直接想象了BiFeO_3中的电开关过程，并演示了BiFeO_3磁区与金属薄层的铁磁区之间的耦合。最近，我们在我们实验室的一名学生生长的Fe2O3外延薄膜中展示了类似的效应。这个由EPSRC资助的DPhil项目将使成功的候选人有机会在不同的方向发展这一系列研究：识别和生长具有电可控磁区的新材料用新方法来转换磁区的磁态，例如通过压电效应。使用电子束光刻和其他无尘室工艺来建立和测试原型设备。该项目可能涉及一系列实验技术，例如：弹性中子散射。我们将主要在卢瑟福·阿普尔顿实验室的ISIS设施中对块状和薄膜样品进行实验。X射线散射，包括硬X射线和软X射线的共振和非共振磁X射线衍射。我们在克拉伦登实验室运行最先进的实验室仪器，但我们的大多数高端实验都是在钻石光源进行的。我们的专长之一是使用克拉伦登实验室的脉冲磁场设备在极高的磁场(高达65T-英国的记录)下进行铁电性测量，但也可以使用一整套更标准的测量。高级显微镜。我们在金刚石上使用光谱显微镜(PEEM)、磁力显微镜(MFM)和磁光克尔效应来成像多功能磁区，这些磁区是氧化物信息存储的基本单元。纳米加工。我们将使用电子束光刻和其他净室方法来设计和建造氧化物量子材料的原型设备。根据候选人的兴趣，该项目还可能包括计算元素。我们与材料部材料模型组合作，使用密度泛函理论方法和其他计算技术来模拟氧化物的功能性质，并预测它们在不同结构中的行为。这个项目属于EPSRC的“能量”、“物理科学”和“量子技术”主题。

One of the most promising routes towards a new generation of fast, low-power electronics is the electrical control of magnetism in insulators. This approach exploits the ability to switch the antiferromagnetic state in several classes of oxides by applying a small writing voltage. The spin polarisation can then be transferred to a ferromagnetic material through an interface, and then read in a conventional way, e.g., using a Tunnelling MagnetoResistance junction as in hard-disk reading heads. This scheme could be employed to produce fast and efficient non-volatile memories, with no writing current to produce Joule heating and therefore dissipate energy. We have recently developed a suite of techniques for simultaneous imaging of antiferromagnetic/ferromagnetic domains and their electrical switching in epitaxial oxide films and devices. We use a combination of synchrotron X-ray diffraction and microscopy, in-house Magnetic Force Microscopy (MFM) and neutron diffraction, which give us access to domains over length scales from 1 cm to < 100 nm. In the past two years, we obtained some very exciting results on thin films and devices of BiFeO3, grown by our collaborators at the University of Madison. In very recent experiments, we directly imagined the process of electrical switching in BiFeO3 and demonstrated the coupling of the BiFeO3 domains with the ferromagnetic domains of a thin metal over-layer. Even more recently, we demonstrated similar effects in epitaxial films of Fe2O3, grown by one of our students in our lab.This EPSRC-funded DPhil project will give the successful candidate the opportunity to develop this line of research in different directions:Identify and grow new materials with electrically controllable domainsExperiment with novel methods to switch the magnetic state of the domains, e.g., through the piezoelectric effect.Build and test prototype devices using electron beam lithography and other clean room processes.This project is likely to involve a combination of experimental techniques, such as:Elastic neutron scattering. We will perform experiments on bulk and films samples predominantly at the ISIS facility at Rutherford Appleton Laboratory.X-ray scattering, including resonant and non-resonant magnetic X-ray diffraction with hard and soft X-rays. We run state-of-the-art laboratory instrumentation in the Clarendon Laboratory, but we perform most of our high-end experiment at the Diamond Light source.Dielectric and transport measurements. One of our specialities is to perform measurements of ferroelectricity in extremely high magnetic fields (up to 65 T - a record in the UK), using the pulsed-magnetic-field facility in the Clarendon Laboratory, but a complete set of more standard measurements is also available.Advanced microscopy. We employ spectral microscopy (PEEM) at Diamond, Magnetic Force Microscopy (MFM) and the Magneto-Optical Kerr Effect to image multi-functional domains, which are the fundamental unit of information storage in oxides.Nanofabrication. We will be using electron beam lithography and other clean-room methods to design and build prototype oxide quantum materials devices.Depending on the candidate's interests, the project may also include a computational element. In collaboration with the Materials Modelling Group in the Department of Materials, we employ Density Functional Theory methods and other computational techniques to model the functional properties of oxides and to predict their behaviour in different architectures.This project falls within the 'Energy', 'Physical Sciences' and 'Quantum Technology' EPSRC themes.