Tunnel anisotropic magnetoresistance for magnetic recording

为了满足日益增长的数据存储需求，将需要更大的面密度，而这只能通过在较小的位上写入数据来实现。然而，这带来了使用当前硬盘驱动器(HDD)中的传统读取器来读取位的挑战。唯一的解决方案是减小电流隧道磁阻(TMR)传感器的宽度，当磁(亚)晶格相对于晶场旋转时，这会导致态密度在费米能级上发生变化，从而导致隧道各向异性磁阻(TAMR)。这只能用具有很强自旋轨道相互作用的材料来实现，如CoPt[1]。基于TAMR的MTJ只需要一个磁极，而传统的TMR传感器是通过MTJ中的反平行和平行态产生的，需要两个铁磁(FM)电极[2]。基于AFM(IrMn)的磁隧道结(MTJ)在低温下获得了大量的TAMR信号(160%)。这比使用过渡金属调频的TAMR传感器大2个数量级[3]。如果这可以在室温下优化，它将允许实现具有单个磁性电极的读取器，从而消除了对第二个FM电极的需要，从而减少了整个读取器的宽度。将探索侧重于TAMR应用的MTJ，其中将在FM的顶部生长反铁磁体(AFM)。这将允许在AFM的顶部生长MTJ，并最终在顶部安装非磁性电极。新的金属间化合物AFM合金的性质引起了人们对AFM自旋电子学的兴趣，因此，我们将重点研究它们的电流开关能力。最后，这些金属间化合物MTJ将在室温下进行优化，以用于重要的TAMR应用。该项目的目的是研究TAMR结，重点是优化AFM材料，以在室温下显示高TAMR；还可能开发新的AFM材料。在整个项目中将使用一系列技术。薄膜磁控溅射沉积将被用来生长材料。一旦生长，将使用振动样品磁强计(VSM)和超导量子干涉装置(SQUID)来研究薄膜的磁性。利用X射线衍射仪(X射线衍射仪)和扫描电子显微镜(SEM)对其结构特征进行了研究。MTJ还需要进行光刻微细加工和传输测量。用于磁性纳米材料的原子自旋模拟软件吸血鬼将被用来模拟实验结果，这反过来将有助于确认实验结果。这将通过使用文献中的参数以及通过样品特性确定的参数来实现。该项目将涉及与希捷技术公司的密切合作，这将包括与斯普林敦工厂的研发团队进行定期互动，以及暴露和使用他们的制造设备。这将为已确定的结果提供更广泛的背景，以及它们如何影响更广泛的真实行业背景。Letts100,087204(2008年)[2]--自然传播。8：449(2017)[3]--自然垫。10347(2011)

In order to meet the demand for increasing data storage needs, will require larger areal densities which can only be achieved by writing the data on smaller bits. However, this brings along the challenge of reading the bits using conventional readers in current hard disk drives (HDDs). The only solution to this is to reduce the width of current tunnel magnetoresistance (TMR) sensors.When a magnetic (sub)lattice rotates with respect to the crystal field, this causes the density of states to change at the Fermi level which results in tunnel anisotropic magnetoresistance (TAMR). This can only be done with materials that have strong spin orbit interactions such as CoPt [1]. TAMR based MTJ only require 1 magnetic electrode in comparison to conventional TMR sensors which are generated by the antiparallel and parallel states in MTJs that require two ferromagnetic (FM) electrodes [2].An AFM (IrMn) based magnetic tunnel junctions (MTJ) achieved massive (160%) TAMR signals at low temperature. This is up to 2 magnitudes greater than TAMR sensors which use transition metal FM [3]. If this can be optimised at room temperature; it would allow for a reader with a single magnetic electrode to be implemented which removes the need for a 2nd FM electrode therefore reducing the width of the overall reader.MTJs with an emphasis on TAMR applications will be explored whereby an antiferromagnet (AFM) will be grown on top of a FM. This will allow the MTJ to be grown on top of the AFM and finally topped with a non-magnetic electrode. The properties of new intermetallic AFM alloys have sparked interest in AFM spintronics and so, these will be investigated with an emphasis on their ability to switch by an electric current. Finally, these intermetallic MTJs will be optimised at room temperature for significant TAMR application.The aim of the project is to investigate TAMR junctions with an emphasis on the optimisation of AFM materials to show high TAMR at room temperature; new AFM materials may also be explored.A range of techniques will be used throughout this project. Thin film magnetron sputtering deposition will be used to grow the materials. Once grown, the magnetic properties of the films will be investigated using vibrating sample magnetometer (VSM) and superconducting quantum interference device (SQUID). Then the structural characteristics will be explored using x-ray diffraction (XRD) and scanning electron microscopy (SEM). Lithographic microfabrication and transport measurements will also be required for the MTJs.The atomistic spin simulation software, Vampire, which is for magnetic nanomaterials will be used to model the experimental results which in turn will assist in confirming the experimental results. This will be achieved with the use of parameters taken from literature as well as the parameters determined through sample characterisation.The project will involve working closely with Seagate Technology which will include regular interaction with the research & development team in the Springtown facility as well as exposure and use of their fabrication equipment. This will provide a broader context to the results that are determined and how they affect the wider real industry context.[1] - Phys. Rev. Letts 100, 087204 (2008)[2] - Nature Communications. 8: 449 (2017) [3] - Nature Mat. 10, 347 (2011)