Rational design of 2D organic magnets with giant magnetic anisotropy based on two-coordinate 5d transition metals

Jianpei Xing,Xue Jiang,Zhou Jiang,Yi Wang,Jijun Zhao,Peng Wang

doi:10.1063/5.0010822

Abstract

As a new class of single-molecule magnets, two-coordinate complexes of open-shell transition metals are comparatively rare and have attracted interest due to their high degree of coordinative unsaturation. However, the dynamic distortion associated with the low coordination number of the metal center hinders the applications of high-density information storage, quantum computing, and spintronics. Here, we propose a series of stable 2D metal–organic frameworks constructed by ideal (1, 3, 5)-benzenetricarbonitrile (TCB) molecules and 5d transition metals (Hf, Ta, W, Re, Os, and Ir) with a highly symmetrical ligand field and rigid π conjugated framework. Among them, TCB-Re exhibits intrinsic ferromagnetic ordering with a considerably large magnetic anisotropic energy (MAE) of 19 meV/atom and high Curie temperature (TC) of 613 K. Under biaxial strain, diverse magnetic states (such as ferromagnetic, paramagnetic, and antiferromagnetic states) can be achieved in TCB-Re by the complicated competition between the in-plane d–px/y–d and out-of-plane d–pz–d superexchange interactions. At a small compressive strain of 0.5%, the MAE for perpendicular magnetization increases substantially to 120 meV/atom; meanwhile, the magnetization and TC above room temperature are well retained. Our results not only extend two-coordinate transition metal complexes to continuous 2D organic magnets but also demonstrate an effective method of strain engineering for manipulating the spin state and MAE.

Highlights

Magnetic materials have been widely developed for information storage, mainly motivated by the commercial desire to increase the magnetic storage density
Jena’s group found that, by applying an external electric field or a biaxial tensile strain, a magnetic anisotropic energy (MAE) value as high as 140 meV can be achieved on phthalocyanine sheets decorated by 5d transition metal atoms such as Os and Ir
We propose that the above-mentioned advantageous characteristics for data storage can be manifested in a class of 2D metal–organic frameworks (MOFs), which is composed by (1, 3, 5)-benzenetricarbonitrile and 5d transition metal (TCB-TM) (TM = Hf, Ta, W, Re, Os, and Ir), namely, C18H6N6TM3

Summary

INTRODUCTION

Magnetic materials have been widely developed for information storage, mainly motivated by the commercial desire to increase the magnetic storage density. The dimension of the magnetic materials has to decrease from traditional three-dimensional (3D) to 2D, 1D, or even a single atom. To this end, the magnetic anisotropic energy (MAE) of these magnets, namely, the energy difference between different magnetized orientations, must be large enough. The dimension of the magnetic materials has to decrease from traditional three-dimensional (3D) to 2D, 1D, or even a single atom.3–5 To this end, the magnetic anisotropic energy (MAE) of these magnets, namely, the energy difference between different magnetized orientations, must be large enough. Ruiz-Díaz’s group found that the MAE reaches up to 5.2 meV/atom for the system of the Fe single layer capped with the Pt layer, much larger than that of conventional bulk Fe crystals with only 10−3 meV/atom.26 Another method for MAE enhancement is to properly introduce elements with strong SOC, especially 4d- or 5d-transition metals. Jena’s group found that, by applying an external electric field or a biaxial tensile strain, a MAE value as high as 140 meV can be achieved on phthalocyanine sheets decorated by 5d transition metal atoms such as Os and Ir.. Our present results indicate that strain is an effective way to improve the MAE of 2D MOFs and rise a novel opportunity for magnetic state controlling

COMPUTATIONAL METHODS

Findings

AND DISCUSSION