Efficient Magnon Transport in Insulating Antiferromagnets Governed by Domain Structures and Doping

Abstract

With high frequency spin dynamics, 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 study the spin transport in 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]. We find that the strain introduced by the growth process tilts the antiferromagnetic anisotropy axis, leading to complex signals across the full temperature range investigated [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]. While mechanisms for the long-distance propagation of pure spin currents carried by the antiferromagnetic order [5, 6] have been developed for thin film antiferromagnets, experimentally the long distance transport of angular momentum by magnons has previoulsy not been achieved [7]. Making use of hematite thin films, a robust magnon current can propagate with intrinsic diffusion lengths of hundreds of nanometres [8]. The efficiency of the transport mechanisms can be tuned by the domain structure, the growth orientation, and the relative orientations of the magnetic field and magnetic anisotropies. Finally, we achieve room temperature magnon transport, where the films present an easy plane anisotropy, by dilute substitution of the ferric ions in order to alters the magnetic anisotropy axes of the thin films.