[Paper Review] High Curie temperature half metallic 2D M2Se3 (M = Co, Ni, and Pd) monolayers with superior mechanical flexibility

Peng Lv, Gang Tang+6 more|arXiv (Cornell University)|May 19, 2018

2D Materials and Applications77 references16 citations

TL;DR

This study investigates two-dimensional M2Se3 monolayers (M = Co, Ni, Pd) using density functional theory, revealing that Co2Se3 exhibits half-metallic ferromagnetism with a Curie temperature exceeding 700 K and exceptional mechanical flexibility due to a unique buckled hinge-like structure, enabling a critical strain twice that of conventional 2D materials, making it highly promising for flexible high-density spintronic devices.

ABSTRACT

Pursuing two-dimensional (2D) intrinsic ferromagnetism with high Curie temperature and great mechanical flexibility has attracted great interest in flexible spintronics. In the present work, we carried out a density functional theory (DFT) investigation on the 2D M2Se3 (M=Co, Ni and Pd) monolayers to understand their structural stabilities, electronic, magnetic and mechanical properties. Our results show that the Co2Se3 monolayer exhibits a fascinating half-metallic ferromagnetism with high Curie temperature (>700K). In addition, due to their unique buckling hinge-like structure, M2Se3 monolayers possess the large out-of-plane negative Poisson's ratio (NPR) and superior mechanical flexibility evidenced by their unusual critical strain two times greater than the well-known 2D materials. These findings imply that 2D M2Se3 family is the promising materials for the applications in the flexible and high-density spintronic nanodevices.

Motivation & Objective

• To explore the structural, electronic, magnetic, and mechanical properties of 2D M2Se3 monolayers (M = Co, Ni, Pd) for potential use in flexible spintronic applications.
• To identify intrinsic two-dimensional ferromagnetic materials with high Curie temperatures suitable for room-temperature and beyond operation.
• To evaluate the mechanical flexibility of M2Se3 monolayers, particularly their resistance to fracture under strain.
• To determine whether these materials exhibit half-metallic behavior, essential for spintronic applications requiring 100% spin polarization.
• To assess the potential of M2Se3 as a platform for high-density, flexible nanoelectronic devices with robust magnetic and mechanical stability.

Proposed method

• Employed density functional theory (DFT) with the generalized gradient approximation (GGA) to calculate electronic and magnetic properties.
• Used the projector augmented wave (PAW) method for electron-ion interactions and a 12×12×1 k-point mesh for Brillouin zone sampling.
• Evaluated structural stability through formation energy and phonon dispersion calculations.
• Analyzed mechanical properties using the in-plane elastic modulus and Poisson's ratio under uniaxial strain.
• Calculated the critical strain by applying increasing tensile strain until the system becomes mechanically unstable.
• Assessed half-metallic behavior via spin-polarized band structure analysis, identifying a gap in the spin-down channel.

Experimental results

Research questions

• RQ1 Do M2Se3 monolayers (M = Co, Ni, Pd) exhibit intrinsic two-dimensional ferromagnetism with high Curie temperatures?
• RQ2 What is the mechanical flexibility of M2Se3 monolayers, particularly their critical strain and Poisson's ratio?
• RQ3 Do these materials display half-metallic character, indicating potential for spintronic applications?
• RQ4 How does the unique buckled hinge-like structure influence the mechanical and electronic properties?
• RQ5 Can these materials sustain large deformations without structural failure, enabling flexible device integration?

Key findings

• The Co2Se3 monolayer exhibits half-metallic ferromagnetism with a Curie temperature exceeding 700 K, indicating potential for high-temperature spintronic applications.
• All M2Se3 monolayers (Co, Ni, Pd) display a large out-of-plane negative Poisson's ratio (NPR), indicating unusual mechanical softness and enhanced flexibility.
• The critical strain of M2Se3 monolayers is approximately twice that of conventional 2D materials like graphene, indicating superior mechanical robustness.
• The unique buckled hinge-like structure is responsible for the enhanced mechanical flexibility and negative Poisson's ratio behavior.
• Phonon dispersion calculations confirm structural stability for all M2Se3 monolayers, with no imaginary modes observed.
• The spin-polarized band structure of Co2Se3 shows a clear band gap in the spin-down channel and metallic behavior in the spin-up channel, confirming half-metallic character.