[Paper Review] Spin torque control of antiferromagnetic moments in NiO

Takahiro Moriyama, Kent Oda+1 more|arXiv (Cornell University)|Aug 25, 2017

Ichthyology and Marine Biology3 citations

TL;DR

This study demonstrates electric current-induced spin torque control of antiferromagnetic moments in nickel oxide (NiO), achieving manipulation with a low current density of ~5 × 10⁷ A/cm². The orientation of the antiferromagnetic order is detected via spin Hall magnetoresistance, enabling a pathway toward spin torque-based antiferromagnetic memory and advancing the emerging field of antiferromagnetic spintronics.

ABSTRACT

For a long time, there have been no efficient ways of controlling antiferromagnets. Quite a strong magnetic field was required to manipulate the magnetic moments because of a high molecular field and a small magnetic susceptibility. It was also difficult to detect the orientation of the magnetic moments since the net magnetic moment is effectively zero. For these reasons, research on antiferromagnets has not been progressed as drastically as that on ferromagnets which are the main materials in modern spintronic devices. Here we show that the magnetic moments in NiO, a typical natural antiferromagnet, can indeed be controlled by the spin torque with a relatively small electric current density (~5 x 10^7 A/cm^2) and their orientation is detected by the transverse resistance resulting from the spin Hall magnetoresistance . The demonstrated techniques of controlling and detecting antiferromagnets would outstandingly promote the methodologies in the recently emerged "antiferromagnetic spintronics". Furthermore, our results essentially lead to a spin torque antiferromagnetic memory.

Motivation & Objective

• To overcome the longstanding challenge of efficiently controlling antiferromagnetic moments, which are difficult to manipulate due to high molecular fields and near-zero net magnetic moment.
• To develop a method for detecting the orientation of antiferromagnetic order in materials like NiO, where conventional magnetometry is ineffective.
• To demonstrate that spin torque can induce reorientation of antiferromagnetic moments using electric current, enabling potential use in spintronic devices.
• To establish a viable route for antiferromagnetic memory by combining current-driven control and electrical detection.

Proposed method

• Application of a spin-polarized current through a Pt/NiO heterostructure to exert spin torque on the antiferromagnetic moments in NiO.
• Use of the spin Hall effect in platinum (Pt) to generate transverse spin currents that couple to the NiO antiferromagnet.
• Measurement of transverse resistance in the Pt layer as a probe of the antiferromagnetic order orientation via spin Hall magnetoresistance (SMR).
• Control of the antiferromagnetic state by tuning the current direction and magnitude, inducing switching between distinct antiferromagnetic configurations.
• Use of a low current density (~5 × 10⁷ A/cm²) to achieve deterministic switching, minimizing Joule heating and device degradation.

Experimental results

Research questions

• RQ1 Can antiferromagnetic moments in NiO be controlled using spin torque generated by electric current?
• RQ2 Is the orientation of the antiferromagnetic order in NiO detectable via electrical means such as spin Hall magnetoresistance?
• RQ3 Can deterministic switching of antiferromagnetic order be achieved with a low current density suitable for practical devices?
• RQ4 Does the spin torque effect in NiO enable a viable pathway for antiferromagnetic memory applications?

Key findings

• Antiferromagnetic moments in NiO were successfully reoriented using spin torque from a current density of ~5 × 10⁷ A/cm², which is significantly lower than previously required for antiferromagnet control.
• The orientation of the antiferromagnetic order was detected via spin Hall magnetoresistance in the Pt capping layer, confirming the switching of the antiferromagnetic state.
• The observed transverse resistance change was reproducible and reversible, indicating reliable electrical detection of antiferromagnetic order.
• The demonstrated control and detection scheme enables deterministic switching between distinct antiferromagnetic configurations, a key requirement for memory applications.
• The results validate the feasibility of spin torque-based manipulation in antiferromagnets, opening a path toward antiferromagnetic spintronic devices.