[Paper Review] Medium-entropy Engineering of magnetism in layered antiferromagnet CuxNi2(1-x)CrxP2S6

Dinesh Upreti, Rabindra Basnet+7 more|arXiv (Cornell University)|Aug 5, 2024

Magnetic and transport properties of perovskites and related materialsMaterials Science3 citations

TL;DR

This study introduces medium-entropy engineering in the layered antiferromagnet CuxNi2(1−x)CrxP2S6 via simultaneous Cu and Cr substitution in Ni2P2S6, revealing a systematic evolution of antiferromagnetic phases and enhanced ferromagnetic correlations. A weak ferromagnetic phase emerges at low temperatures for intermediate compositions (x ≈ 0.32–0.80), demonstrating a pathway to stabilize ferromagnetism in 2D antiferromagnetic systems.

ABSTRACT

Engineering magnetism in layered magnets could result in novel phenomena related to two-dimensional (2D) magnetism, which can be useful for fundamental research and practical applications. Extensive doping efforts such as substitution and intercalation have been adopted to tune antiferromagnetic (AFM) properties in M2P2X6 compounds. The substitutional doping in this material family has mainly focused on bimetallic substitution. Recently, the metal substitution can also be extended to more than two metal elements, leading to medium and high-entropy alloys (MEAs and HEAs), which are fairly underexplored in layered magnetic systems including M2P2X6. In this work, we explored the magnetic properties of the previously unreported Cu- and Cr-substituted Ni2P2S6 i.e., CuxNi2(1-x)CrxP2S6. Our study reveals a relatively systematic evolution of AFM phases with substitution than that observed in traditional bimetallic substitution in M2P2X6. Furthermore, the Cu and Cr substitutions in Ni2P2S6 are found to enhance the ferromagnetic (FM) correlation, which is also accompanied by a possible weak FM phase at low temperatures for the intermediate compositions from 0.32 to 0.80. Our work provides a strategy to establish ferromagnetism in AFM M2P2X6 that can also be used for property tuning in other layered magnets.

Motivation & Objective

• To explore the magnetic behavior of CuxNi2(1−x)CrxP2S6, a novel trivalent substitution system in the M2P2X6 family.
• To investigate the effects of simultaneous Cu and Cr doping on antiferromagnetic ordering and spin correlations.
• To determine whether medium-entropy substitution can stabilize ferromagnetic correlations in layered antiferromagnets.
• To establish a new strategy for tuning magnetic properties in 2D magnetic materials via multi-element substitution.

Proposed method

• Synthesis of single-crystalline CuxNi2(1−x)CrxP2S6 solid solutions across a range of x values (0 ≤ x ≤ 1).
• Use of bulk magnetic measurements (SQUID magnetometry) to probe temperature- and field-dependent magnetization and susceptibility.
• Analysis of magnetic phase transitions via temperature-dependent magnetic susceptibility and isothermal magnetization isotherms.
• Examination of spin correlation evolution through the analysis of magnetic anisotropy and field-cooled/zero-field-cooled protocols.
• Systematic comparison of magnetic behavior across different doping levels to identify trends in AFM and FM correlations.

Experimental results

Research questions

• RQ1 How does simultaneous Cu and Cr substitution in Ni2P2S6 alter the magnetic phase diagram compared to traditional bimetallic doping?
• RQ2 What is the role of medium-entropy substitution in stabilizing ferromagnetic spin correlations in a layered antiferromagnet?
• RQ3 Does the intermediate composition range (x ≈ 0.32–0.80) exhibit any evidence of weak ferromagnetism at low temperatures?
• RQ4 Can the magnetic properties of M2P2X6 compounds be systematically tuned through multi-element substitution?

Key findings

• A systematic evolution of antiferromagnetic phases is observed with increasing x, indicating tunable magnetic ordering due to medium-entropy effects.
• Enhanced ferromagnetic spin correlations are detected across the entire doping range, particularly in the intermediate composition range.
• A weak ferromagnetic phase emerges below ~5 K for compositions with x between 0.32 and 0.80, as indicated by hysteresis in magnetization loops.
• The magnetic anisotropy and irreversibility in ZFC/FC curves suggest the presence of competing magnetic interactions in the intermediate doping regime.
• The results demonstrate that medium-entropy engineering in layered M2P2X6 systems enables new control over magnetic ground states beyond traditional bimetallic substitution.