Tunnel anisotropic magnetoresistance for magnetic recording

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)