The nano engineering and spintronic technologies (NEST) group focuses on understanding the physical processes and developing the fundamental understanding necessary to create the computational and data storage devices of the future.

Our research includes exploring recent device ideas in non-conventional computing and encompasses a broad range of activities to explore the spin of electrons in nanoscale magnetic structures. The group interacts strongly with the Henry Royce Institute for advanced materials and the National Graphene Institute. We regularly use large scale facilities in the UK and Europe for neutron and X-ray scattering and have wide range of collaborators in the UK and Europe.

In addition to the group's leading edge deposition, device fabrication and characterisation facilities we have full access to the state-of-the-art facilities at the National Graphene Institute and the Royce institute.

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Bye Charley!

This week we said a sad farewell to Charley after six years (PhD student and RA) in the group. We had a group lunch to say our farewells. Good luck Charley in your new career.

New Paper in Advanced Functional Materials

We are collaborators on a paper titled “Remotely Actuated Magnetic Nanocarpets for Bone Tissue Engineering: Non-invasive Modulation of Mechanosensitive Ion Channels for Enhanced Osteogenesis” by A. R. Unnithan, A. R. K. Sasikala, B. K. Shrestha, A. Lincoln, T. Thomson, A. J. El Haj. You can view the paper online here.

Abstract: Non-invasive approaches using remotely controllable nanomaterials have demonstrated their potential ability to enhance treatment efficacy in regen- erative medicine and tissue repair. Although magnetic nanoparticles (MNPs) have been used for multiple healthcare applications where their remote control properties can show significant advances, enhanced surface functional groups, and electrical properties would expand their capabilities. To address this, in this study, MNPs incorporated Graphene Oxide (GO) based nanocomposites (GOMNPs) are developed and functionalized with TREK1 and Piezo1 antibodies to specifically target the respective mechanosensitive ion channels. Magnetic ion channel activation (MICA) technology is used to remotely activate MG63 osteoblast-like cells tagged with these functionalized GOMNPs. Remote activation of mechanotransduction pathways shows significant upregulation in osteogenic gene expression as well as enhanced alkaline phosphate activity and calcium mineralization with enhanced bone formation. The development of a GOMNP composite has extensive applicability for future clinical translation.

New Research Paper in Nature Scientific Reports

Congratulations to Michael Grimes who has had his latest research published in Nature Scientific Reports: “Determination of sub-ps lattice dynamics in FeRh thin films” by M. Grimes, H. Ueda, D. Ozerov, F. Pressacco, S. Parchenko, A. Apseros, M. Scholz, Y. Kubota, T. Togashi, Y. Tanaka, L. Heyderman, T. Thomson and V. Scagnoli. You can view the paper online here.

Abstract: Understanding the ultrashort time scale structural dynamics of the FeRh metamagnetic phase transition is a key element in developing a complete explanation of the mechanism driving the evolution from an antiferromagnetic to ferromagnetic state. Using an X-ray free electron laser we determine, with sub-ps time resolution, the time evolution of the (–101) lattice diffraction peak following excitation using a 35 fs laser pulse. The dynamics at higher laser fluence indicates the existence of a transient lattice state distinct from the high temperature ferromagnetic phase. By extracting the lattice temperature and comparing it with values obtained in a quasi-static diffraction measurement, we estimate the electron–phonon coupling in FeRh thin films as a function of laser excitation fluence. A model is presented which demonstrates that the transient state is paramagnetic and can be reached by a subset of the phonon bands. A complete description of the FeRh structural dynamics requires consideration of coupling strength variation across the phonon frequencies.

New Research Paper in AIP Advances

Well done to Michale Grimes for having his latest research published in AIP Advances: “X-ray investigation of long-range antiferromagnetic ordering in FeRh” by M. Grimes, N. Gurung, H. Ueda, D. G. Porter, B. Pedrini, L. J. Heyderman, T. Thomson, and V. Scagnol. You can view the paper online here.

Abstract: We demonstrate a probe of long-range antiferromagnetic (AF) order in FeRh thin films using non-resonant magnetic x-ray scattering. In particular, x-rays at energies below the Fe K-edge have been used for the observation of magnetic Bragg peaks. Due to the low efficiency of the magnetic scattering, a grazing incidence geometry was used to optimise the diffracted intensity from the thin film samples. Based on Scherrer analysis, we estimate a coherence length similar to previous reports from x-ray magnetic linear dichroism (XMLD) experiments, indicating that domain sizes are limited to 40 nm which is consistent with the grain size. The temperature dependent behaviour of the AF order shows an inverse correlation with the emergence of the ferromagnetic (FM) moment, as expected from the phase diagram.

Magnetism 2022

It was great to be able to attend a face-to-face conference for the first time in a while as the group members descended on York to attend Magnetism 2022, which took place at the University of York on 28th-29th March. We have staff and students presenting talks and displaying posters. We all enjoyed the conference dinner on the evening of the 28th!

New Paper in Nature Scientific Reports

We have had a research paper “Repeatable and deterministic all electrical switching in a mixed phase artificial multiferroic” by W. Griggs, and T. Thomson, published in Nature Scientific Reports. You can view the paper online here.

Abstract: We demonstrate a repeatable all-electric magnetic switching behaviour in a PMN-PT/FeRh thin film artificial multiferroic. The magnitude of the effect is significantly smaller than expected from conventional thermomagnetic switching of FeRh thin films and we explore properties of the PMN-PT/FeRh system in order to understand the origin of this reduction. The data demonstrate the importance of the crystallographic phase of PMN-PT and show how a phase transition at ~ 100 °C modifies the magneto-electric coupling. We demonstrate a large strain remanence effect in the PMN-PT substrate, which limits the magnetoelectric coupling on successive cycling of the applied electric field..

New Paper in Applied Physics Letters

We have had a research paper “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, published in Applied Physics Letters. 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 paper in Phys. Rev. Materials

We have had a Research Update “Polarized neutron reflectometry characterization of interfacial magnetism in an FePt/FeRh exchange spring” by W. Griggs, C. Bull, C. W. Barton, R. A. Griffiths, A. J. Caruana, C. J. Kinane, P. W. Nutter, and T. Thomson, published in Phys. Rev. Materials. You can view the paper online here.

Abstract: We report on the depth-sensitive, temperature-dependent exchange coupling in an FePt/FeRh thin-film exchange-spring structure. The depth-dependent in-plane magnetization is measured as a function of applied magnetic field and sample temperature using polarized neutron reflectometry (PNR). The magnetization profiles are interpreted in terms of the competition between anisotropy, exchange coupling, and dipolar coupling as the FeRh undergoes the magnetic phase transition from antiferromagnetic to ferromagnetic ordering. The PNR data are combined with bulk magnetometry and x-ray characterization, allowing us to determine characteristic length scales over which the exchange-spring mechanism is effective at ambient and elevated temperatures.

New Research Update in APL Materials

We have had a Research Update “Spintronic terahertz emitters: Status and prospects from a materials perspective” by C. Bull, S. M. Hewett, R. Ji, C-H. Lin, T. Thomson, D. W. Graham, and P. W Nutter, published in APL Materials, which has been selected as the Editor’s Pick. You can view the paper online here.

The mechanism of THz emission from a bilayer spintronic emitter.

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.