Dr Aidan Hindmarch, MPhys, PhD.
(email at firstname.lastname@example.org)
As a new(ish) member of staff I currently enjoy a reduced (2/3) teaching load. I supervise Level 2 laboratory skills, electronics lab., and long lab. projects, and lecture Level 2 electronics. I am Level 1/Level 2 'Bridge project' coordinator. I currently supervise two Level 4 research project students working in experimental nanomagnetism and spintronics.
Conventional electronics utilises only the charge of the electron: Spintronics additionally uses the intrinsic 'spin' of the electron as a further state variable to process, convey, and store information. Novel spintronic device architectures promise both enhanced capabilities and reduced power consumption: one outcome of this so-far is the massive increase in magnetic data-storage capacity in recent years, which has enabled high data-capacity consumer technologies such as personal media players, internet email and data storage, and high-definition television-on-demand services. My research centres around the fundamental physical mechanisms underpinning spin-polarized electrical conduction and magnetism in nanostructured spintronic devices. This is achieved using a combination of magnetic and electrical measurements, in conjunction with synchrotron x-ray and neutron scattering techniques.
Spin-polarised currents naturally arise in ferromagnetic metals. However, the effects which are useful in harnessing such currents for spintronics - spin-coherence, electrostatic screening, and evanescent decay lengths; electron mean-free-paths; magnetic domain-wall widths etc. - typically involve lengthscales on the nanometer scale. The passage of spin-polarised currents through a device is intrinsically linked to the detailed electronic structure of materials, making it possible to probe fundamental quantum-mechanical effects in magnetic nanostructures from something as simple as electrical resistance measurements. In order to study and exploit spin-polarised currents it is often necessary to fabricate thin-film or multilayered magnetic devices: magnetic thin-films and nanostructures present a wealth of novel and interesting physics in themselves. One aspect in which I am interested is hybrid structures combining metallic magnetic materials with semiconductors: incorporating the spin degree of freedom in inorganic semiconductor (Si, GaAs etc.) devices allows extension of traditional functionality, whilst organic semiconductors provide the scope for spintronic functionality to be added in future low-cost printable and flexible electronics.
Thin-film and Interface magnetism
Nanomaterials bridge the gap between individual atoms and bulk material: Thin-films, consisting sometimes of only a few atomic monolayers, can exhibit very different electrical and magnetic properties than their bulk counterparts due to symmetry breaking at surfaces and interfaces reducing the dimensionality of the system, whereas in nanoclusters long-range translational symmetry is entirely removed. The competition surface/interface and volume effects means that varying film thicknesses or cluster sizes over only a very small, even sub-nanometer, range can result in drastic modification to how materials behave. This provides an ideal method to engineer suitable magnetic properties for a given device application. Much of my research in this are centred on the magnetic anisotropy found in magnetic metal-inorganic semiconductor hybrid contacts: forming an atomically abrupt interface between nanoscale layers of different classes of material often produces novel, interesting, and technologically useful effects.
Deposition and fabrication of thin-film devices
Functionality of many of the layered structures relevant for present and future spintronic devices relies heavily on the exact structure of the device materials on an atomic scale: crystal structure and orientation; abrupt, smooth layer interfaces and pattern definition etc., in addition to avoiding damage to the underlying material or structure during fabrication. In addition to a degree of control required in order to fabricate modern devices, the material growth techniques employed must also be suitable for the high throughput, rapid turnaround manufacturing processes required for large-scale industrial application.
Synchrotron x-ray & neutron scattering
Large scale facilities provide the ability to investigate both structure and magnetism in nanomaterials and devices. Synchrotron techniques allow element-specific structural and magnetic characterisation, in addition to nanoscale imaging. Neutron reflectivity methods are used to determine vector magnetization depth-profiles of buried structures and interfaces. National and international facilities are used in my research, including the ISIS neutron source and Diamond Light Source (UK), and the US National Synchrotron Light Source. Using these techniques provides many opportunities to understand the underlying physics behind the many magnetic interactions which can occur at surfaces and interfaces: with this understanding we are then able to tailor the material properties to provide enhanced performance and functionality in future devices (Image courtesy of NSLS, Brookhaven National Laboratory).
Indicators of Esteem
- 2013: Invited speaker: Joint Korea-UK spintronics workshop, Rutherford Appleton Laboratory, UK.
- 2012: EPSRC Manufacturing the Future theme: Selected as one of the first members of the new Early Career Forum for Manufacturing Research.
- 2012: Institute of Physics: Honorary Treasurer of IOP Magnetism group
- 2012: Invited speaker: Joint Korea-UK spintronics workshop, Seoul, South Korea.
- 2012: University research infrastructure funding: funding awarded by the university to begin setting up a laboratory for thin-film deposition.
- 2011: Institute of Physics: Elected member of Magnetism subject group committee.
- 2011: Invited review article: Topical review on 'Interface magnetism in ferromagnet-compound semiconductor hybrid structures' for the inaugural issue of the spintronics and nanomagnetism journal 'Spin'.
Journal papers: academic
- T. D. Skinner, H. Kurebayashi, D. Fang, D. Heiss, A. C. Irvine, A. T. Hindmarch, M. Wang, A. W. Rushforth & A. J. Ferguson (2013). Enhanced inverse spin-Hall effect in ultrathin ferromagnetic/normal metal bilayers. Applied Physics Letters 102(7): 072401.
- V. Harnchana, A. T. Hindmarch, M. C. Sarahan, C. H. Marrows, A. P. Brown & R. M. D. Brydson (2013). Evidence for boron diffusion into sub-stoichiometric MgO (001) barriers in CoFeB/MgO-based magnetic tunnel junctions. Journal of Applied Physics 113(16): 163502.
- M. Wang, A.W. Rushforth, A.T. Hindmarch, R.P. Campion, K.W. Edmonds, C.R. Staddon, C.T. Foxon & B.L. Gallagher (2013). Magnetic and structural properties of (Ga,Mn)As/(Al,Ga,Mn)As bilayer films. Applied Physics Letters 102(11): 112404.
- Ciudad, D., Wen, Z.-C., Hindmarch, A.T., Negusse, E., Arena, D.A., Han, X.-F. & Marrows, C.H. (2012). Competition between cotunneling, Kondo effect, and direct tunneling in discontinuous high-anisotropy magnetic tunnel junctions. Phys. Rev. B 85: 214408.
- Hindmarch, A.T., Parkes, D.E. & Rushforth, A.W. (2012). Fabrication of metallic magnetic nanostructures by argon ion milling using a reversed polarity planar magnetron ion source. Vacuum 86(10): 1600-1604.
- D. E. Parkes, S. A. Cavill, A. T. Hindmarch, P. Wadley, F. McGee, C. R. Staddon, K. W. Edmonds, R. P. Campion, B. L. Gallagher & A. W. Rushforth (2012). Non-volatile voltage control of magnetization and magnetic domain walls in magnetostrictive epitaxial thin films. Applied Physics Letters 101(7): 072402.
- Hindmarch, AT (2011). Interface magnetism in ferromagnetic metal-compound semiconductor hybrid structures. Spin 1(1): 45-69.
- Hindmarch, AT, Rushforth, AW, Campion, RP, Marrows, CH & Gallagher, BL (2011). Origin of in-plane uniaxial magnetic anisotropy in CoFeB amorphous ferromagnetic thin -films. Physical Review B (Brief Report) 83(21): 212404.
- Hindmarch, AT, Harnchana, V, Walton, AS, Brown, AP, Brydson, RMD & Marrows, CH (2011). Zirconium as a boron sink in crystalline CoFeB:MgO:CoFeB magnetic tunnel junctions. Applied Physics Express 4(1): 013002.
- Hindmarch, AT, Dempsey, KJ, Ciudad, D, Negusse, E, Arena, DA & Marrows, CH (2010). Fe diffusion, oxidation, and reduction at the CoFeB:MgO interface studied by soft x-ray absorption spectroscopy and magnetic circular dichroism. Applied Physics Letters 96(9): 092501.
- Sidorenko, AA, Pernechele, C, Lupo, P, Ghidini, M, Solzi, M, De Renzi, R, Bergenti, I, Graziosi, P, Dediu, V, Hueso, L & Hindmarch, AT (2010). Interface effects on an ultrathin Co film in multilayers based on the organic semiconductor Alq3. Applied Physics Letters 97(17): 162509.
- Hindmarch AT, Harnchana V, Ciudad D, Negusse E, Arena DA, Brown AP, Brydson RMD & Marrows CH (2010). Magnetostructural influences of thin Mg insert layers in crystalline CoFe(B):MgO:CoFe(B) magnetic tunnel junctions. Applied Physics Letters 97(25): 252502.
- Seemann, KM, Makrousov, Y, Aziz, A, Miguel, J, Kronast, F, Kuch, W, Blamire, MG, Hindmarch AT, Hickey, BJ, Souza, I & Marrows, CH (2010). Spin-Orbit Strength Driven Crossover between Intrinsic and Extrinsic Mechanisms of the Anomalous Hall Effect in the Epitaxial L10-Ordered Ferromagnets FePd and FePt. Physical Review Letters 104(7): 076402
- Hindmarch, AT, Kinane, CJ, MacKenzie,M, Chapman, JN, Henini, M, Taylor, D, Arena, DA, Dvorak, J, Hickey, BJ & Marrows, CH (2008). Interface induced uniaxial magnetic anisotropy in amorphous CoFeB films on AlGaAs(001). Physical Review Letters 100(11): 117201.
- Centre for Materials Physics
- Inorganic Electroactive Materials Group
- Nanoscale Science and Technology Group
- X-ray Scattering and Magnetism Group