Engineering ultrafast spin currents and terahertz transients by magnetic heterostructures

TL;DR

This paper demonstrates how magnetic heterostructures can be engineered to control the shape and duration of ultrafast spin currents and terahertz transients, enabling high-speed spintronic devices and broadband THz emitters.

Contribution

It introduces a method to manipulate femtosecond spin-current bursts using tailored magnetic heterostructures with different electron mobilities.

Findings

Ru cap layer produces longer spin-current pulses

Spin current shape can be controlled by heterostructure design

Potential for high-speed spintronic and broadband THz applications

Abstract

In spin-based electronics, information is encoded by the spin state of electron bunches. Processing this information requires the controlled transport of spin angular momentum through a solid, preferably at frequencies reaching the so far unexplored terahertz (THz) regime. Here, we demonstrate, by experiment and theory, that the temporal shape of femtosecond spin-current bursts can be manipulated by using specifically designed magnetic heterostructures. A laser pulse is employed to drive spins from a ferromagnetic Fe thin film into a nonmagnetic cap layer that has either low (Ru) or high (Au) electron mobility. The resulting transient spin current is detected by means of an ultrafast, contactless amperemeter based on the inverse spin Hall effect that converts the spin flow into a THz electromagnetic pulse. We find that the Ru cap layer yields a considerably longer spin-current pulse because electrons are injected in Ru d states that have a much smaller mobility than Au sp states. Thus, spin current pulses and the resulting THz transients can be shaped by tailoring magnetic heterostructures, which opens the door for engineering high-speed spintronic devices as well as broadband THz emitters in particular covering the elusive range from 5 to 10THz.