Electrical control of magnetism in oxide films and devices

迈向新一代快速、低功耗电子产品的最有希望的途径之一是对绝缘体中的磁性进行电气控制。这种方法利用了通过施加一个小的写入电压来切换几种氧化物的反铁磁状态的能力。然后，自旋极化可以通过界面转移到铁磁性材料上，然后以传统方式读取，例如，使用硬盘读取头中的隧道磁电阻结。该方案可用于生产快速高效的非易失性存储器，没有写入电流产生焦耳加热，因此耗散能量。我们最近开发了一套技术，用于在外延氧化膜和器件中同时成像反铁磁/铁磁畴及其电开关。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，这使我们能够访问长度范围从1厘米到< 100纳米的域。在过去的两年里，我们在BiFeO3的薄膜和器件上取得了一些非常令人兴奋的成果，这些成果是由我们在麦迪逊大学的合作者们开发的。在最近的实验中，我们直接想象了BiFeO3中的电开关过程，并演示了BiFeO3域与薄金属覆盖层的铁磁域的耦合。最近，我们在Fe2O3的外延膜中证明了类似的效果，这是由我们的一个学生在我们的实验室中生长的。这项由epsrc资助的博士项目将为成功的候选人提供机会，在不同的方向上发展这条研究路线：识别和生长具有可控畴的新材料；用新颖的方法来切换畴的磁性状态的实验，例如，通过压电效应。使用电子束光刻和其他洁净室工艺建立和测试原型设备。这个项目可能涉及多种实验技术，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设施中对散装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使用最先进的实验室仪器，但我们在钻石光源进行大多数高端实验。介电和输运测量。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65 T -英国的记录）下进行铁电性测量，但也有一整套更标准的测量方法。先进的显微镜。我们使用光谱显微镜（PEEM），磁力显微镜（MFM）和磁光克尔效应来成像多功能畴，这些多功能畴是氧化物中信息存储的基本单元。我们将使用电子束光刻和其他洁净室方法来设计和构建原型氧化物量子材料器件。根据候选人的兴趣，项目也可能包括计算元素。与材料系材料建模组合作，我们采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特性，并预测它们在不同架构中的行为。该项目属于EPSRC的“能源”、“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.