Structural sensitivity of the spin Hall magnetoresistance in antiferromagnetic thin films

Abstract

Reading the magnetic state of antiferromagnetic (AFM) thin films is key for AFM spintronic devices. We investigate the underlying physics behind the spin Hall magnetoresistance (SMR) of bilayers of platinum and insulating AFM hematite (α-Fe 2 O 3 ) and find an SMR efficiency of up to 0.1%, comparable to ferromagnetic-based structures. To understand the observed complex SMR field dependence, we analyze the effect of misalignments of the magnetic axis that arise during growth of thin films, by electrical measurements and direct magnetic imaging, and find that a small deviation can result in significant signatures in the SMR response. This highlights the care that must be taken when interpreting SMR measurements on AFM spin textures.

Orthogonal interlayer coupling in an all-antiferromagnetic junction

“…2a SMR signals of a control sample Fe 2 O 3 (12)/Pt(4) (units in nanometers), where the magnetic eld (H) and current (I) is along x-axis and the spin polarization generated by the spin Hall effect of Pt is along y-axis. As expected, comparatively low resistance states at high magnetic elds re ect that the Néel vector (n) of Fe 2 O 3 is perpendicular to H (I) due to the spin-op at high elds and deviates towards H (I) at low elds, which is quite characteristic for negative SMR of AFM [17][18][19][20] . The resistance peaks at approximately µ 0 H = ±0.35 T owing to the deviation of n from the spin-op state appears at a negative eld as sweeping the eld from positive to negative (black line), indicating that the Néel vector almost keeps the spin-op state at zero-eld 16 .…”

“…The resistance peaks at approximately µ 0 H = ±0.35 T owing to the deviation of n from the spin-op state appears at a negative eld as sweeping the eld from positive to negative (black line), indicating that the Néel vector almost keeps the spin-op state at zero-eld 16 . Note that Fe 2 O 3 with the thickness below tens of nanometers maintains easy-plane anisotropy without Morin transition 16,18,20 2e], resulting in the absorption of spin current and the second resistance peak (iii). It should be clari ed that the second peak can exist when the coupling energy is large enough to overcome the Zeeman energy of the top Fe 2 O 3 at the valley (ii), otherwise the n (top Fe 2 O 3 ) will maintain spin-op state rather than deviating towards n // H. The magnitude of the second peak is smaller than the rst one can be ascribed to less component of n along x-axis.…”

“…As a pioneering work, it is highly signi cant to use AFM with Néel vectors that are accessible to control and readout for the coupling layers. α-Fe 2 O 3 is a high-Néel-temperature antiferromagnet 14 with a weak in-plane anisotropy and concomitant low spin-op eld 15,16 , as well as sizable spin Hall magnetoresistance (SMR) signals to record its Néel vector [17][18][19][20][21] . Here, we demonstrate unprecedented orthogonal coupling of Néel vectors (Fig.…”

Emergence of zero-field non-synthetic single and catenated antiferromagnetic skyrmions in thin films

“…Intrinsic AFM meronic spin-textures (complexes made of half-skyrmions) were recently detected in bulk phases 6,7,54 while synthetic AFM skyrmions were found within multilayers 5 . However, the observation of intrinsic AFM skyrmions has so far been elusive, in particular at surfaces and interfaces, where they are highly desirable for racetrack concepts.…”

Exceptional sign changes of the nonlocal spin Seebeck effect in antiferromagnetic hematite

“…Finally, we develop a toy model of thermal transport in hematite, where we are able to resolve some of the key experimental observations. We utilize α-Fe 2 O 3 because it has been shown to facilitate long-distance magnon transport excited by in interfacial spin-bias [3][4][5][6], a low magnetic damping [6,27] and a controllable magnetic order in bulk crystals and thin films [28][29][30]. Below the Morin temperature [31], this material adopts an easy-axis (EA) anisotropy where the Néel vector n aligns parallel to the crystallographic c-axis [28,29].…”