Andrew Ross
With spin dynamics in the THz regime, stability in the presence of external magnetic fields, and a lack of stray fields, antiferromagnetic materials are positioned to become key in future low power spintronic devices [1]. Here, we grow and investigate high quality thin films of hematite (α-Fe2O3) (< 500 nm) of different orientations. Through measurements of the spin Hall magnetoresistance in hematite/Pt bilayers, the magnetic anisotropies of the thin films can be extracted, and the critical temperature of the Morin transition from the easy plane to the easy axis antiferromagnetic phase is electrically observed [2, 3]. Whilst a key part of antiferromagnetic spintronics is to encode and read information in the Néel vector, the efficient transfer of information is crucial for integration of antiferromagnets into devices. Recently, we demonstrated that a diffusive magnon current can be carried over micrometres in antiferromagnetic single crystals, but such crystals are not suitable for spintronic devices [4,5]. Despite theoretical works investigating the mechanisms for the long-distance propagation of pure spin currents carried by the antiferromagnetic order [6, 7], studies on thin film antiferromagnets making use of single-frequency or broadband excitations have failed to achieve efficient transport of angular momentum by magnons [8]. Making use of hematite thin films, a robust magnon current can propagate with intrinsic diffusion lengths of hundreds of nanometres. The efficiency of the transport mechanisms can be tuned by field cycling of the domain structure, the growth orientation, and the relative orientations of the magnetic field and magnetic anisotropies. The manner by which the stabilisation of the antiferromagnetic domain structure (see Fig. 1) results in frequency dependent length scales and proves to be critical in the magnon transport will be discussed [9].
[1] T. Jungwirth et al., Nat. Phys. 14, 200-203 (2018)[2] R. Lebrun et al., Comm. Phys. 2 50 (2019)
[3] A. Ross et al., arXiv:2001.03117 (2020)
[4] R. Lebrun, A. Ross et al., Nature 561, 222-225 (2018)
[5] R. Lebrun et al., arxiv: 2005.14414 (2020)
[6] S. Takei et al., Phys. Rev. B, 90, 94408 (2014)
[7] S. Bender et al., Phys. Rev. Lett. 19, 056804 (2017)
[8] H. Wang et al., Phys. Rev. B 91, 220410 (2015)
[9] A. Ross, R. Lebrun et al., Nano Lett. 20 1, 306-313 (2020)