Terahertz spin-to-charge conversion in ferromagnetic Ni nanofilms

Area of Science:

• Spintronics
• Condensed Matter Physics
• Materials Science

Background:

• Spintronic terahertz (THz) emission relies on spin-to-charge conversion (SCC) in ferromagnet (FM)/nonmagnet (NM) heterostructures.
• Multiple SCC mechanisms exist, but materials exhibiting several simultaneously are rare.

Purpose of the Study:

• To investigate the multifaceted role of nickel (Ni) films in spintronic THz emission.
• To explore diverse SCC mechanisms within Ni-based heterostructures.

Main Methods:

• Fabrication and THz emission experiments on single Ni layers, FM/Ni, Ni/NM bilayers, and FM/Ni/NM trilayers.
• Analysis of THz emission originating from various SCC processes.

Main Results:

• Ni monolayer exhibits THz emission via anomalous Hall effect and ultrafast demagnetization.
• In FM/Ni, Ni acts as an SCC implementer, primarily via inverse spin Hall effect (ISHE) in Ni.
• In Ni/NM, Ni injects spin currents converted by NM's ISHE.
• In FM/Ni/NM, THz emission involves ISHE across multiple interfaces, with Ni thickness influencing dominance.

Conclusions:

• Ferromagnetic Ni films possess dual functionality as spin injectors and SCC implementers.
• This dual role enables multiple THz emission mechanisms within a single material system.
• Presents a new paradigm for designing advanced spintronic THz emitters.