In the final two years of activity within TRANSPIRE, the work was focused on producing thin films and stacks of low-moment, highly polarized materials (including the prototypical Mn2RuGa), but also on confirming direct THz emission from magnetisation precession in ultra-thin and granular films, as well as testing a new possible route to produce a THz oscillator, based on single-layer spin-orbit torque.
TCD optimized thin films of the manganese-rich, tetragonal Heuslers. New batches of blanket material were sent to the partners in HZDR for patterning. The new approach to exciting spin dynamics uncovered in Y2 by TCD and NTNU, i.e. the single-layer spin-orbit-torque-based devices, became the primary focus in an attempt to reach TRANSPIRE's over-arching goal of creating on-chip THz oscillators and detectors.
The partners HZDR-Deac group, patterned more than 10 different variations of the new STT-MTJ stacks into measurable devices (with contacts suitable for wire-bonding). These were all tested first at HZDR and then at TCD. The overall results showed a minor improvement of room TMR ratio (up to 10 %, at RT) on individual junctions, while the majority of devices were failing to operate properly.
The work on THz spectroscopy - using both laser-in/THz out and THz-in/THz-out methods continued at pace in the HZDR-Kovalev group. The THz-driven resonances (for example in Mn3Ga films) were confirmed to be much narrower (by a factor of ~4), down to 7 GHz, when compared to laser-driven dynamics on the same films. Newly prepared samples (from Trifolium Dubium) of Mn2Ga, in both continuous and island (granular) conformation, were also investigated.
The theory work in TRANSPIRE, actually benefitted from lockdown time in the final period. It was decided to pursue a different approach: computation of electron transport through ordered models of magnetic tunnel junctions using NEGF-DFT.
A number of PhD thesis works are now submitted, which are based on work done in TRANSPIRE. A corresponding set of Manuscript is also being prepared for publication. It is projected that some of the data (both experimental and computational) gathered within TRANSPIRE will be subject to publication for a couple of years past the nominal end of the programme. The materials research findings, not published as research papers, will be made fully openly available on the materials.ie platform, established for TRANSPIRE. The domain transpire.eu will be maintained for a number of years past the end of the programme, to act as a locator for information not available through the EC servers and not committed to open publication databases (such as the TARA archive).
