[Paper Review] Efficient field-free perpendicular magnetization switching by a magnetic spin Hall effect

Shuai Hu, Ding‐Fu Shao+7 more|arXiv (Cornell University)|Mar 16, 2021

Magnetic properties of thin films42 references4 citations

TL;DR

This paper demonstrates efficient, field-free switching of perpendicular magnetization in Ni/Co multilayers using the magnetic spin Hall effect in noncollinear antiferromagnets like Mn3Sn. An in-plane charge current generates an out-of-plane spin current with spin polarization due to the magnetic group symmetry of Mn3Sn, producing a deterministic anti-damping torque that enables low-current, field-free switching, outperforming conventional spin-orbit torque devices in efficiency and reliability.

ABSTRACT

Current induced spin-orbit torques driven by the conventional spin Hall effect are widely used to manipulate the magnetization. This approach, however, is nondeterministic and inefficient for the switching of magnets with perpendicular magnetic anisotropy that are demanded by the high-density magnetic storage and memory devices. Here, we demonstrate that this limitation can be overcome by exploiting a magnetic spin Hall effect in noncollinear antiferromagnets, such as Mn3Sn. The magnetic group symmetry of Mn3Sn allows generation of the out-of-plane spin current carrying spin polarization induced by an in-plane charge current. This spin current drives an out-of-plane anti-damping torque providing deterministic switching of perpendicular magnetization of an adjacent Ni/Co multilayer. Compared to the conventional spin-orbit torque devices, the observed switching does not need any external magnetic field and requires much lower current density. Our results demonstrate great prospects of exploiting the magnetic spin Hall effect in noncollinear antiferromagnets for low-power spintronics.

Motivation & Objective

• To overcome the inefficiency and nondeterminism of conventional spin-orbit torque devices in switching perpendicular magnets with high anisotropy.
• To explore the potential of noncollinear antiferromagnets like Mn3Sn for generating spin currents with out-of-plane spin polarization.
• To achieve deterministic, field-free switching of perpendicular magnetization using a magnetic spin Hall effect with minimal current density.
• To demonstrate a scalable, low-power alternative to conventional spin-transfer torque and spin-orbit torque memory devices.

Proposed method

• Utilization of the magnetic spin Hall effect in Mn3Sn, a noncollinear antiferromagnet with broken inversion symmetry.
• Application of an in-plane charge current to generate a transverse, out-of-plane spin current with spin polarization due to the magnetic group symmetry.
• Integration of the Mn3Sn layer with a Ni/Co multilayer to enable spin-transfer torque via the generated spin current.
• Measurement of magnetization switching dynamics using time-resolved Kerr microscopy to confirm field-free, deterministic switching behavior.
• Quantification of switching efficiency through current density dependence and comparison with conventional spin-orbit torque devices.
• Use of symmetry analysis and first-principles calculations to confirm the origin of the magnetic spin Hall effect in Mn3Sn.

Experimental results

Research questions

• RQ1 Can the magnetic spin Hall effect in noncollinear antiferromagnets like Mn3Sn enable efficient, field-free switching of perpendicular magnetization?
• RQ2 What is the role of magnetic group symmetry in generating out-of-plane spin currents from in-plane charge currents?
• RQ3 How does the switching efficiency of the magnetic spin Hall effect compare to conventional spin-orbit torque in terms of current density and reliability?
• RQ4 Can deterministic switching be achieved without external magnetic fields using this mechanism?
• RQ5 What is the fundamental limit of current density required for reliable switching using this approach?

Key findings

• The magnetic spin Hall effect in Mn3Sn generates a robust out-of-plane spin current with spin polarization under an in-plane charge current, enabling effective spin torque.
• The induced anti-damping torque enables deterministic, field-free switching of perpendicular magnetization in adjacent Ni/Co multilayers.
• Switching is achieved at significantly lower current densities compared to conventional spin-orbit torque devices, demonstrating superior energy efficiency.
• The switching process is nondeterministic in conventional spin-orbit torque systems but becomes deterministic due to the symmetry-protected spin current in Mn3Sn.
• Theoretical analysis confirms that the magnetic group symmetry of Mn3Sn is essential for the generation of the out-of-plane spin current.
• The results demonstrate a viable pathway toward low-power, high-density spintronic memory and logic devices.