Electric field driven switching of individual magnetic skyrmions (1601.02935v1)

Abstract: Controlling magnetism with electric fields is a key challenge to develop future energy-efficient devices, however, the switching between inversion symmetric states, e.g. magnetization up and down as used in current technology, is not straightforward, since the electric field does not break time-reversal symmetry. Here, we demonstrate that local electric fields can be used to reversibly switch between a magnetic skyrmion and the ferromagnetic state. These two states are topologically inequivalent, and we find that the direction of an electric field directly determines the final state. This observation establishes the possibility to combine energy-efficient electric field writing with the recently envisaged skyrmion racetrack-type memories.

• The paper demonstrates electric field-driven switching of individual skyrmions in a thin Fe film using a non-magnetic STM tip.
• It quantifies a critical electric field of 1-6 V/nm that reversibly converts skyrmion states, ensuring precise magnetic control.
• The study shows that 1 V/nm simulates a 40 mT magnetic effect, highlighting the potential for low-energy spintronic devices.

Electric Field Driven Switching of Individual Magnetic Skyrmions: A Summary

The paper by Hsu et al. investigates the utilization of local electric fields to switch between magnetic skyrmions and ferromagnetic states within a thin film of iron (Fe) on iridium (Ir) substrate. This represents a significant stride towards energy-efficient data storage and logic devices in the field of spintronics, an area of technology reliant on the electron spin. The authors explore the control of magnetic states via electric fields, bypassing the constraints posed by time-reversal symmetry that has typically hindered such transitions in conventional magnetic states.

Research Overview

The paper employs a model system consisting of a three-atomic-layer-thick epitaxial Fe film on an Ir(111) substrate, capitalizing on the naturally occurring spin spirals and skyrmions. Magnetic skyrmions, distinguished by their topological distinctness, present a promising alternative to traditional ferromagnetic states due to their stability and unique spin texture. These states are stabilized in materials by the Dzyaloshinskii-Moriya interaction (DMI), promoting non-collinear spin configurations aligned with spintronic applications.

In their experimental work, the authors demonstrate that electric fields can be used to toggle between skyrmionic and ferromagnetic phases, a feat conventionally dependent on locally injected spin-polarized currents. They methodically establish that variations in sample bias voltage induce these transitions and that the process's directionality (writing or deleting skyrmions) is determined by the voltage polarity. By employing a non-magnetic tungsten (W) tip in conjunction with a scanning tunneling microscopy (STM) setup, the researchers unequivocally confirm that the switching is driven by the electric field, ruling out contributions from spin-polarized currents.

Key Results and Findings

Several imperative results were unveiled in this paper:

1. The critical electric field required for switching is quantified between 1 and 6 V/nm, as mapped through systematic variance of parameters.
2. The switching mechanism shows a dependency on the electric field strength rather than spin-transfer torque contributions, as confirmed by experiments with non-magnetic tips.
3. The authors identify a correspondence where 1 V/nm of electric field equates to an effect akin to a 40 mT magnetic field, underscoring the potential for electric field-driven mechanisms to replace or supplement magnetic fields in future devices.

Implications and Future Directions

This research significantly impacts the roadmap for skyrmion-based spintronic devices, suggesting that electric fields can serve as a robust and energy-efficient means for encoding information at the nanoscale. The possibility of locally switching skyrmionic states without engendering undesired movements in the storage medium opens up novel device architectures.

The theoretical implications are broad, laying the groundwork for further exploration into the interactions between electric fields and skyrmionic topologies. There arise questions regarding the scalability of these effects to other material systems and multi-skyrmion scenarios. Future iterations could also probe the dynamic behaviors of skyrmions under pulsed or alternating electric fields and evaluate their stability and longevity under operational conditions typical in computational devices.

In conclusion, Hsu et al.'s work demonstrates a pivotal method for manipulating nanoscale magnetic structures, advancing the discourse on magnetic skyrmion technology and their application in low-energy data manipulation. As the field progresses, this approach could be seminal in overcoming current electronic device limitations, particularly in data density and energy consumption.