Tune of Magnetism and Electronic Structures of Alkali Metal Carbides with Rocksalt Structure

TL;DR

This study investigates how pressure and doping influence the magnetic and electronic properties of alkali metal carbides with rocksalt structure, revealing tunable magnetic states and phase transitions through computational analysis.

Contribution

It provides a detailed computational analysis of how pressure and doping can tune magnetism and electronic structures in alkali metal carbides, introducing the possibility of spin gapless semiconductors.

Findings

Pressure induces insulator-metal transition.

Doping with IIA elements reduces magnetic moments.

Hydrostatic pressure can create spin gapless semiconductors.

Abstract

Electronic structures of carbides with the rocksalt structure were calculated by full potential electronic codes solving the Kohn-Sham equation. Bonding characters were analyzed by constructing tight-binding Hamiltonian based on maximally-localized Wannier functions. It was found that the cations in these compounds act as an electron provider and the frame is formed by the carbon atoms. The electronic states in the vicinity of the Fermi level are mainly from the p-orbitals of C. Pressure and doping are two efficient ways to tune the magnetic and electronic properties of these compounds. It turns out that a spin gapless semiconductor can be obtained by applying hydrostatic pressure up to tens of gigaPascal. Higher pressure induced an insulator to metal transition because of band broadening. Compounds of IA group (Na, K, Rb, Cs) were magnetic semiconductor at ambient conditions. Alloying with IIA elements decrease the magnetic moment according to the law of $3-x$, where $x$ is the relative atomic ratio of the IIA elements to the IA ones. The behaviors of the compounds under the pressure and the doping effects can be understood by a rigid band model.