Impact of gigahertz and terahertz transport regimes on spin propagation and conversion in the antiferromagnet IrMn

TL;DR

This study investigates how spin transport and conversion in the antiferromagnet IrMn differ between gigahertz and terahertz frequencies, revealing shorter spin propagation lengths at THz frequencies and emphasizing interface effects for ultrafast spin control.

Contribution

It provides the first detailed comparison of spin transport regimes in IrMn at GHz and THz frequencies, highlighting the transition from diffusive to ballistic transport and the role of interfaces.

Findings

Spin propagation length is ~4 times shorter at THz frequencies (~0.5 nm) than at GHz (~2 nm).

THz spin currents exhibit sub-picosecond dynamics, indicating ultrafast transport.

Interface effects significantly influence spin-to-charge conversion, especially at THz frequencies.

Abstract

Control over spin transport in antiferromagnetic systems is essential for future spintronic applications with operational speeds extending to ultrafast time scales. Here, we study the transition from the gigahertz (GHz) to terahertz (THz) regime of spin transport and spin-to-charge current conversion (S2C) in the prototypical antiferromagnet IrMn by employing spin pumping and THz spectroscopy techniques. We reveal a factor of 4 shorter characteristic propagation lengths of the spin current at THz frequencies (~ 0.5 nm) as compared to the GHz regime (~ 2 nm) which may be attributed to the ballistic and diffusive nature of electronic spin transport, respectively. The conclusion is supported by an extraction of sub-picosecond temporal dynamics of the THz spin current. We also report on a significant impact of the S2C originating from the IrMn/non-magnetic metal interface which is much more pronounced in the THz regime and opens the door for optimization of the spin control at ultrafast time scales.