EPSRC DTP PhD studentship: Sensing the magnetization dynamics of a nanostructured thin film with a nearfield optical antenna

Location: University of Exeter, Streatham Campus, Exeter, Devon

Project Description:

Time resolved microscopy is a powerful tool by which to understand the dynamic behaviour of a microelectronic device. With today’s lithographic fabrication techniques routinely producing sub-micron feature sizes, a non-invasive dynamic probe with deep sub-nanoscale resolution is required. We have constructed a near-field time-resolved optical microscope in which an optical antenna is mounted on a transparent atomic force microscope (AFM) tip so that light from a femtosecond laser may be confined within a near-field spot on the sample surface. This internationally unique instrument is an ideal platform on which to test near field antennas designed to interact with specific types of material or device. For example, an antenna capable of receiving and transmitting orthogonal linear polarisation states is required to sense the response of magnetic and chiral materials. The antennas will fabricated by focused ion beam (FIB) milling of gold-coated atomic force microscope tips made from a transparent quartz-like material. The sensing of magnetic materials is of immediate interest to our collaborators in the magnetic data storage industry with our collaborative research on magnetic films and devices [1,2] benefiting from the enhanced spatial resolution offered by the new probe.

The role of the student within the project will be to lead the design, fabrication and characterisation of the AFM tips. Finite element modelling of the electromagnetic field distribution will be used to determine the optimum geometry of cross-shaped aperture antennas before they are realized by FIB milling. Optical microspectrometry will be used to characterize the resonances exhibited by the antenna and so ensure that they are well matched to the wavelengths of the scanning laser microscope. The student will also carry out initial magneto-optical testing of the antennas in a static Kerr microscope (SKM), using the AFM attachment, before they are deployed within the time resolved SKM, where the student will work alongside an experienced postdoctoral fellow. The project will provide experience of advanced nano-fabrication techniques, numerical modelling, and the use of polarizing optics and ultrafast lasers. There will be opportunity to interact with research engineers from an industrial environment and the student will gain skills that are highly marketable in the broad area of microelectronic technology. The project builds upon fabrication and measurement techniques that have already been demonstrated within Exeter, and so rapid progress is expected in the optimisation of the antenna design so that thesis submission should occur within 42 months.

[1] “Observation of vortex dynamics in arrays of nanomagnets”, W. Yu, P. S. Keatley, P. Gangmei, M. K. Marcham, T. H. J. Loughran, R. J. Hicken, S. A. Cavill, G. van der Laan, J. R. Childress and J. A. Katine, Phys. Rev. B 91, 174425 (2015).

[2] “Imaging the equilibrium state and magnetization dynamics of partially-built hard disk write heads”, R. A. J. Valkass, W. Yu, L. R. Shelford, P. S. Keatley, T. H. J. Loughran, R. J. Hicken, S. A. Cavill, G. van der Laan, S. S. Dhesi, M. A. Bashir, M. A. Gubbins, P. J. Czoschke, and R. Lopusnik, Appl. Phys. Lett. 106, 232404 (2015).