Two-dimensional ferromagnetic superlattices.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Spintronics

Background:

• Two-dimensional ferromagnetic materials (2D FMs) exhibit long-range ferromagnetic order and topological skyrmions.
• Dimensionality effects significantly reduce the Curie temperature (T_C) in few-layer 2D FMs compared to bulk materials.
• Enhancing T_C in wafer-scale 2D FMs is crucial for practical applications.

Purpose of the Study:

• To explore effective approaches for enhancing the Curie temperature (T_C) of two-dimensional ferromagnetic materials (2D FMs).
• To investigate interfacial proximity-induced effects on T_C in wafer-scale 2D FMs.
• To enable the development of practical ultra-thin spintronic devices.

Main Methods:

• Fabrication of (Fe₃GeTe₂/CrSb)_n superlattices using molecular-beam epitaxy on 2-inch wafers.
• Elemental-specific X-ray magnetic circular dichroism (XMCD) measurements to probe magnetic properties.
• Density functional theory (DFT) calculations to understand interfacial coupling and electronic effects.

Main Results:

• Significant enhancement of T_C in 4-layer Fe₃GeTe₂ from 140 K to 230 K due to interfacial ferromagnetic coupling with CrSb.
• Observation of an inverse proximity effect, inducing a ferrimagnetic state in the interfacial CrSb layer.
• Further T_C enhancement to near room temperature achieved by introducing excess Fe in the Fe₃GeTe₂/CrSb superlattice.

Conclusions:

• Interfacial proximity coupling with CrSb effectively enhances the T_C of few-layer 2D FMs in a wafer-scale format.
• The inverse proximity effect in CrSb and DFT calculations confirm the mechanism of T_C enhancement.
• This approach offers a viable route for realizing advanced ultra-thin spintronic devices operating at higher temperatures.