Spin Seebeck Imaging of Spin-Torque Switching in Antiferromagnetic Pt/NiO Heterostructures

Abstract

As electrical control of Néel order opens the door to reliable antiferromagnetic spintronic devices, understanding the microscopic mechanisms of antiferromagnetic switching is crucial. Spatially resolved studies are necessary to distinguish multiple nonuniform switching mechanisms; however, progress has been hindered by the lack of tabletop techniques to image the Néel order. We demonstrate spin Seebeck microscopy as a sensitive tabletop method for imaging antiferromagnetism in thin films and apply this technique to study spin-torque switching inPt/NiOandPt/NiO/Ptheterostructures. We establish the interfacial antiferromagnetic spin Seebeck effect in NiO as a probe of surface Néel order. By imaging before and after applying current-induced spin torque, we resolve spin domain rotation and domain wall motion. We correlate the changes in spin Seebeck images with electrical measurements of the average Néel orientation through the spin Hall magnetoresistance, confirming that we image antiferromagnetic order.

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Plain Language Summary

In an antiferromagnet, adjacent electron spins point in opposite directions. Although antiferromagnetic memory devices can potentially operate at terahertz speeds, they are notoriously difficult to manipulate since there is no net magnetic moment. Recent experiments show that an electrical current can switch the spin orientation, but the switching is complicated and spatially nonuniform, requiring imaging to better understand the process. Most imaging studies of antiferromagnetism rely on coherent x rays from a synchrotron facility. We demonstrate a simple, powerful tabletop technique for directly imaging antiferromagnetic spin order in the insulator NiO and then image current-induced switching inPt/NiOandPt/NiO/Ptdevices.

Our technique is based on the coupling between spin and heat. We make use of a temperature drop at thePt/NiOinterface, induced by pulsed laser heating, to create an electrical signal that depends on the local spin orientation and resolve micrometer-size antiferromagnetic spin domains within a thin film of NiO. By taking images after applying a current, we show that spin domains rotate, move, grow, and shrink in response to the current. We find that some domains rotate without changing direction when the direction of the current is reversed, while other domains move back and forth with the current.

Our results provide a new understanding of how to manipulate antiferromagnetic order in NiO, and we expect our imaging technique to extend to a wide variety of antiferromagnetic materials.