New Publication in APL

Well done to my PhD student Simmone Hewett (so-supervised) who has had her first paper published in Applied Physics Letters, which is a great achievement! The title of the paper is “Spintronic terahertz emitters exploiting uniaxial magnetic anisotropy for field-free emission and polarization control” by S. M. Hewett, C. Bull, A. M. Shorrock, C-H. Lin, R. Ji, M. T. Hibberd, T. Thomson, P. W. Nutter, and D. G. Graham. You can view the paper online here.

Abstract: We explore the terahertz (THz) emission from CoFeB/Pt spintronic structures in the below-magnetic-saturation regime and reveal an orientation dependence in the emission, arising from in-plane uniaxial magnetic anisotropy (UMA) in the ferromagnetic layer. Maximizing the UMA during the film deposition process and aligning the applied magnetic field with the easy axis of the structure, allows the THz emission to reach saturation under weaker applied fields. In addition, the THz emission amplitude remains at saturation levels when the applied field is removed. The development of CoFeB/Pt spintronic structures that can emit broadband THz pulses without the need for an applied magnetic field is beneficial to THz magneto-optical spectroscopy and facilitates the production of large-area spintronic emitters. Furthermore, by aligning the applied field along the hard axis of the structure, the linear polarization plane of the emitted THz radiation can be manipulated by changing the magnitude of the applied field. We therefore demonstrate THz polarization control without the need for mechanical rotation of external magnets.

New Publication

We have had a research update published in APL Materials: “Spintronic terahertz emitters: Status and prospects from a materials perspective”, Charlotte Bull Simmone M. Hewett Ruidong Ji Cheng-Han Lin Thomas Thomson Darren M. Graham, and  Paul W. Nutter, APL Materials 9, 090701 (2021). You can download the file (open access) here.

Abstract: Spintronic terahertz (THz) emitters, consisting of ferromagnetic (FM)/non-magnetic (NM) thin films, have demonstrated remarkable potential for use in THz time-domain spectroscopy and its exploitation in scientific and industrial applications. Since the discovery that novel FM/NM heterostructures can be utilized as sources of THz radiation, researchers have endeavored to find the optimum combination of materials to produce idealized spintronic emitters capable of generating pulses of THz radiation over a large spectral bandwidth. In the last decade, researchers have investigated the influence of a wide range of material properties, including the choice of materials and thicknesses of the layers, the quality of the FM/NM interface, and the stack geometry upon the emission of THz radiation. It has been found that particular combinations of these properties have greatly improved the amplitude and bandwidth of the emitted THz pulse. Significantly, studying the material properties of spintronic THz emitters has increased the understanding of the spin-to-charge current conversion processes involved in the generation of THz radiation. Ultimately, this has facilitated the development of spintronic heterostructures that can emit THz radiation without the application of an external magnetic field. In this review, we present a comprehensive overview of the experimental and theoretical findings that have led to the development of spintronic THz emitters, which hold promise for use in a wide range of THz applications. We summarize the current understanding of the mechanisms that contribute to the emission of THz radiation from the spintronic heterostructures and explore how the material properties contribute to the emission process.

Generation of THz radiation from a spintronic bilayer structure composed of a ferromagnetic (FM) thin film and a non-magnetic (NM) thin film

EPSRC THz Spintronics Project

Today my EPSRC-funded project looking at THz spintronic devices has officially started following the new research associate starting … welcome Charley!

Here’s looking forward to entering the world of THz pulse generation and extending the group activities in spintronics.

New KTP started

My new KTP with Titan Products Ltd has started today with the new associate joining the University and the company; welcome Seb.

The aim of the project is to develop, embed and exploit advanced wireless networking expertise to support the commercialisation of a sector-leading family of wireless environmental sensors and control products for the commercial and home automation markets. It is a joint project between the Departments of Computer Science and Electrical & Electronic Engineering, in the School of Engineering, The University of Manchester.

More information can be found on the KTP portal. The total grant for the project is £303k and it will run for 3 years.

New Paper Published – APL Materials

Well done to my PhD student Charley who has had an excellent paper published in APL Materials (IF: 4.296).

PNR study of the phase transition in FeRh thin films,
C Bull, C. W. Barton, W. Griggs, A. Caruana, C. J. Kinane, P. W. Nutter and T. Thomson.
Vol 7, Issue 10, 101117 (2019).

The paper reports on the results of a polarised neutron reflectivity (PNR) study aimed at determining the physical and magnetic structure of FeRh at room temperature and partway through the transition. The PNR results are analysed with reference to X-ray diffraction, X-ray reflectivity, and atomic force microscopy data, which together provide a consistent description of the magnetic and physical state of the FeRh thin films. We demonstrate that the nucleation of the ferromagnetic phase initiates at the MgO substrate, and results from structural and magnetic measurements demonstrate that the magnetic behaviour and strain properties of FeRh correlate with the evolving topography of the three films investigated