Imaging the Néel Vector in Few-Layer CrPS₄ with Second-Harmonic Generation

Area of Science:

• Condensed Matter Physics
• Materials Science
• Magnetism

Background:

• Second-harmonic generation (SHG) is a nonlinear optical technique sensitive to crystal symmetry.
• SHG can probe time-reversal symmetry, enabling studies of magnetic order in materials.
• Layered antiferromagnetic (AFM) materials are of interest for spintronic applications.

Purpose of the Study:

• To investigate the magnetic properties of chromium thiophosphate (CrPS4) using SHG.
• To understand the interplay between crystallographic and magnetic symmetry breaking in CrPS4.
• To explore the potential of SHG for probing AFM order and Néel vector direction.

Main Methods:

• Second-harmonic generation (SHG) spectroscopy on bulk CrPS4.
• Polarization-dependent SHG measurements.
• Polarized SHG microscopy on terraced CrPS4 crystals.

Main Results:

• SHG intensity in CrPS4 breaks both crystallographic and magnetic symmetry below the Néel temperature.
• A specific SHG tensor element was identified, correlating with magnetic order.
• SHG polarization response in even-layer crystals showed history dependence, indicating sensitivity to Néel vector direction.
• AFM order in even-layer regions was found to be dictated by the ferromagnetic order of adjacent odd-layer regions.

Conclusions:

• SHG is a powerful tool for investigating complex magnetic orders in layered AFM materials like CrPS4.
• The study elucidates the relationship between structural and magnetic symmetries and their manifestation in nonlinear optical signals.
• CrPS4 exhibits unique layer-dependent magnetic ordering, influenced by ferromagnetic interactions.