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，这只能通过在更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）中的传统读取器读取位的挑战。解决这一问题的唯一方法是减小隧道磁阻（TMR）传感器的宽度。当磁（子）晶格相对于晶体场旋转时，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电阻（TAMR）。这只能用具有强自旋轨道相互作用的材料来完成，比如CoPt[1]。与传统的TMR传感器相比，基于TAMR的MTJ只需要一个磁电极，而传统的TMR传感器是由MTJ中的反平行和平行状态产生的，需要两个铁磁（FM）电极[2]。一种基于AFM （IrMn）的磁隧道结（MTJ）在低温下获得了大量（160%）的TAMR信号。这比使用过渡金属调频[3]的TAMR传感器高出2个数量级。如果这可以在室温下进行优化；它将允许使用单个磁电极的阅读器，从而消除了对第二个调频电极的需要，从而减少了整个阅读器的宽度。mtj的重点是TAMR应用，将探索反铁磁体（AFM）将生长在FM之上。这将允许MTJ生长在AFM的顶部，最后用非磁性电极覆盖。新型金属间原子力显微镜合金的性能引起了人们对原子力显微镜自旋电子学的兴趣，因此，这些将被研究的重点是它们通过电流开关的能力。最后，这些金属间MTJs将在室温下进行优化，以实现显著的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；新的AFM材料也可以被探索。一系列的技术将在整个项目中使用。薄膜磁控溅射沉积将被用于生长材料。薄膜生长后，将利用振动样品磁强计（VSM）和超导量子干涉装置（SQUID）研究薄膜的磁性能。然后利用x射线衍射（XRD）和扫描电子显微镜（SEM）研究其结构特征。mtj还需要光刻微加工和传输测量。用于磁性纳米材料的原子自旋模拟软件Vampire将用于模拟实验结果，从而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本表征确定的参数来实现。该项目将涉及与希捷科技的密切合作，包括与Springtown工厂的研发团队的定期互动，以及他们的制造设备的曝光和使用。这将为所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实际行业背景。b[1] -物理。自然通讯。8:449(2017).自然学报。10:347 （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)