Strain-induced Isostructural and Magnetic Phase Transitions in Monolayer MoN$_2$

TL;DR

This study predicts that applying biaxial strain to monolayer MoN$_2$ induces isostructural and magnetic phase transitions, changing N-N bonding and magnetic properties, with potential applications in nanoscale devices.

Contribution

It demonstrates that physical strain can induce bond formation and magnetic phase transitions in 2D MoN$_2$, revealing new ways to control material properties.

Findings

Strain causes a sudden drop in N-N distance, indicating bond formation.

Magnetic moments shift from N to Mo sublattice during transition.

Magnetic coupling changes from ferromagnetic to antiferromagnetic.

Abstract

The change of bonding status, typically occurring only in chemical processes, could dramatically alter the material properties. Here, we show that a tunable breaking and forming of a diatomic bond can be achieved through physical means, i.e., by a moderate biaxial strain, in the newly discovered MoN$_2$ two-dimensional (2D) material. Based on first-principles calculations, we predict that as the lattice parameter is increased under strain, there exists an isostructural phase transition at which the N-N distance has a sudden drop, corresponding to the transition from a N-N nonbonding state to a N-N single bond state. Remarkably, the bonding change also induces a magnetic phase transition, during which the magnetic moments transfer from the N(2p) sublattice to the Mo(4d) sublattice, meanwhile the type of magnetic coupling is changed from ferromagnetic to anti-ferromagnetic. We provide a physical picture for understanding these striking effects. The discovery is not only of great scientific interest in exploring unusual phase transitions in low-dimensional systems, but it also reveals the great potential of the 2D MoN$_2$ material in the nanoscale mechanical, electronic, and spintronic applications.