Fully spin-polarized two dimensional polar semi-metallic phase in Eu substituted GdI$_2$ monolayer

TL;DR

This paper predicts a novel 2D Eu-substituted GdI$_2$ monolayer that exhibits ferromagnetism, ferroelasticity, polarity, and full spin polarization, with properties tunable by mechanical strain, making it promising for nano-electronics and spintronics.

Contribution

It introduces a first-principles prediction of a 2D material with coexisting ferroic orders and spin polarization, a rare combination in metallic systems.

Findings

Monolayer GdI$_2$ with Eu substitution is ferromagnetic, polar, and ferroelastic.

External strain can switch the polarization and magnetization directions.

The material is a fully spin-polarized semi-metal with coupled ferroic orders.

Abstract

The coexistence of seemingly mutually exclusive properties such as ferromagnetism, ferroelectricity and metallicity in atomically thin materials is the requirement of the hour in electronics as the Moore's law faces an impending end. Only a few 2D multiferroic materials have been predicted/realized so far. The polar metals with simultaneous presence of polarity and conductivity are also equally rare. Here, we predict, based on first-principles calculations that an Eu-substituted rare-earth halide GdI$_2$ monolayer showcases ferromagnetism, ferroelasticity while being polar and a fully spin-polarized semi-metal at the same time. The ferroelasticity and polarity are shown to be coupled making it possible to switch the polar direction using external mechanical stress. Further, it is observed that, an application of biaxial tensile strain of $5\%$ causes the spin easy-axis to shift from out-of-plane to in-plane direction. Thus spin easy axis gets coupled with the direction of polarization in the strained monolayer making the switching of magnetization also possible using external strain. Simultaneous coexistence and coupling of the ferroic orders in a metallic 2D material makes the Eu substituted GdI$_2$ monolayer an incredibly rare material for nano-electronics and spintronics applications.