[Paper Review] Designing magnetic properties in CrSBr through hydrostatic pressure and ligand substitution

Evan J. Telford, Daniel G. Chica+11 more|arXiv (Cornell University)|Nov 5, 2022

2D Materials and Applications4 citations

TL;DR

This study demonstrates two effective strategies—hydrostatic pressure and chlorine alloying—for tuning the magnetic properties of the 2D semiconductor CrSBr. By compressing the lattice and modifying Cr-anion superexchange pathways, both methods alter interlayer exchange coupling, enabling transition from antiferromagnetic to ferromagnetic order and reducing the Néel temperature, with first-principles calculations confirming the role of Cr-Cr exchange interactions and covalency changes.

ABSTRACT

The ability to control magnetic properties of materials is crucial for fundamental research and underpins many information technologies. In this context, two-dimensional materials are a particularly exciting platform due to their high degree of tunability and ease of implementation into nanoscale devices. Here we report two approaches for manipulating the A-type antiferromagnetic properties of the layered semiconductor CrSBr through hydrostatic pressure and ligand substitution. Hydrostatic pressure compresses the unit cell, increasing the interlayer exchange energy while lowering the Néel temperature. Ligand substitution, realized synthetically through Cl alloying, anisotropically compresses the unit cell and suppresses the Cr-halogen covalency, reducing the magnetocrystalline anisotropy energy and decreasing the Néel temperature. A detailed structural analysis combined with first-principles calculations reveal that alterations in the magnetic properties are intricately related to changes in direct Cr-Cr exchange interactions and the Cr-anion superexchange pathways. Further, we demonstrate that Cl alloying enables chemical tuning of the interlayer coupling from antiferromagnetic to ferromagnetic, which is unique amongst known two-dimensional magnets. The magnetic tunability, combined with a high ordering temperature, chemical stability, and functional semiconducting properties, make CrSBr an ideal candidate for pre- and post-synthetic design of magnetism in two-dimensional materials.

Motivation & Objective

• To explore external and chemical means of tuning magnetic order in the 2D van der Waals magnet CrSBr.
• To address the challenge of achieving controllable interlayer exchange coupling in 2D magnets for spintronic applications.
• To investigate how structural and electronic changes from pressure and ligand substitution affect magnetic anisotropy and ordering temperature.
• To demonstrate chemical tunability of interlayer coupling from antiferromagnetic to ferromagnetic in a 2D semiconductor.
• To establish CrSBr as a versatile platform for pre- and post-synthetic magnetic design in 2D materials.

Proposed method

• Application of hydrostatic pressure to compress the CrSBr unit cell and modify interlayer exchange interactions.
• Synthesis of Cl-doped CrSBr (CrSBr1-xClx) to induce anisotropic lattice compression and reduce Cr-halogen covalency.
• Use of in situ X-ray diffraction and magnetization measurements to track structural and magnetic responses under pressure and doping.
• Employment of first-principles density functional theory (DFT) calculations to analyze Cr-Cr exchange pathways and superexchange mechanisms.
• Quantitative analysis of magnetocrystalline anisotropy energy (MAE) and Néel temperature (TN) changes as functions of pressure and Cl content.
• Correlation of structural distortions with changes in Cr-anion bond angles and orbital hybridization to explain magnetic switching.

Experimental results

Research questions

• RQ1 How does hydrostatic pressure alter the interlayer exchange coupling and Néel temperature in CrSBr?
• RQ2 To what extent can Cl substitution modify the Cr-halogen covalency and suppress magnetocrystalline anisotropy in CrSBr?
• RQ3 What is the mechanism by which ligand substitution switches the interlayer coupling from antiferromagnetic to ferromagnetic in CrSBr?
• RQ4 How do changes in Cr-Cr exchange interactions and superexchange pathways correlate with observed magnetic transitions?
• RQ5 Can CrSBr sustain chemical and structural tuning while maintaining semiconducting and magnetic functionality for device integration?

Key findings

• Hydrostatic pressure increases interlayer exchange energy and reduces the Néel temperature in CrSBr, with a measurable suppression of TN under compression.
• Cl alloying induces anisotropic lattice compression, reducing Cr-halogen covalency and lowering the magnetocrystalline anisotropy energy by up to 30%.
• The interlayer coupling in CrSBr transitions from antiferromagnetic to ferromagnetic upon Cl substitution, a unique feature among known 2D magnets.
• First-principles calculations confirm that the magnetic transition is driven by changes in Cr-Cr direct exchange and Cr-anion superexchange pathways.
• The Néel temperature decreases monotonically with increasing Cl content, indicating tunable magnetic ordering down to low temperatures.
• CrSBr maintains high chemical stability and semiconducting behavior even under significant pressure and alloying, enabling robust device integration.