Propagation Length of Antiferromagnetic Magnons Governed by Domain Configurations

Abstract

Spintronics seeks to functionalize antiferromagnetic materials to develop memory and logic devices operating at terahertz speed and robust against external magnetic field perturbations. To be useful, such functionality needs to be developed in thin film devices. The key functionality of long-distance spin-transport has, however, so far only been reported in bulk single crystal antiferromagnets, while in thin films, transport has so far been limited to a few nanometers. In this work, we electrically achieve a long-distance propagation of spin-information in thin films of the insulating antiferromagnet hematite. Through transport and magnetic imaging, we demonstrate a strong correlation between the efficiency of the transport of magnons, which carry spin-information, and the magnetic domain structure of the films. In thin films with large domains, magnons propagate over micrometer distances whilst they attenuate over much shorter distances in multidomain thin films. The governing factor of the attenuation is related to scattering at domain walls, and we demonstrate that we can reduce this through training by field

Long-distance spin-transport across the Morin phase transition up to room temperature in ultra-low damping single crystals of the antiferromagnet α-Fe2O3

“…Our findings potentially open the transport also to hematite thin films, which are intrinsically mostly in the easy plane phase 37 . Significant further advances in the fabrication of high-quality thin films with large domains are necessary to realize future devices 8 . More generally, insulating antiferromagnets can have magnetic damping as low as the best ferromagnets and can also transport spin information at room temperature over large length scales, which are both key features for magnonic devices.…”

“…Experimental observations of these rich physics have started to emerge, with recent reports of long-distance spin-transport near room temperature in the easy-axis phase of hematite 8,16 and at low temperatures in antiferromagnetic quantum Hall graphene 17 . However, the complex spin-transport features in collinear antiferromagnets are generally not indicative of the coherent transport regime although signatures have recently been claimed 18 .…”

“…Hematite, α-Fe 2 O 3 , is a model system to investigate the spintransport regime of easy-axis antiferromagnets as we recently reported 8,16 but the easy-axis phase is only present at low temperatures. Above the Morin temperature (T Morin = 260 K), undoped hematite single crystals undergo a transition from an easy-axis to an easy-plane AFM, due to a change of sign of its anisotropy field H A 19 , with a small sub-lattice canting due to its internal Dzyaloshinskii-Moriya interaction (DMI) 20 .…”

Negative spin Hall magnetoresistance of Pt on the bulk easy-plane antiferromagnet NiO

“…Moreover, domain walls can interact with the spin current itself leading to domain wall movement 33 and spin current reflection upon domain walls 34 . In thin films with multiple domain walls, the reflection damps the non-local signals, but domain optimization by tuning the growth direction or by magnetic training still leads to micrometer spin transport 35 .…”

Dephasing of transverse spin current in ferrimagnetic alloys

“…1(b)) assumes a spin current without any scattering and simple layer-by-layer alternating collinear magnetic order. Finite scattering, spin-orbit coupling, and complex magnetization states in real materials may disrupt transverse spin coherence [20][21][22]. A shorter overall coherence length 2 results from reduced due to increased spin-flip rates, or reduced due to momentum scattering and non-collinear magnetic order that prevents perfect cancellation of dephasing [20,21].…”