Doping induced itinerant ferromagnetism and enhanced ferroelectricity in BL-InSe

TL;DR

This study predicts that bilayer InSe exhibits coexisting switchable ferroelectricity and doping-induced ferromagnetism, offering a new platform for voltage-tunable multiferroic devices through first-principles calculations.

Contribution

It reveals emergent ferroelectricity and ferromagnetism in bilayer InSe driven by stacking and doping, which was not previously known.

Findings

Spontaneous out-of-plane polarization with low transition barrier.

Doping enhances ferroelectric polarization contrary to screening expectations.

Doping induces itinerant half-metallic ferromagnetism with reversible spin polarization.

Abstract

The microscopic coexistence of ferroelectricity and ferromagnetism in solids remains a fundamental challenge in condensed matter physics, with far-reaching implications for multifunctional materials and next-generation electronic devices. Using first-principles calculations, we predict emergent sliding ferroelectricity and doping-mediated ferromagnetism in bilayer (BL) InSe. The energetically favored AB stacked BL-InSe spontaneously breaks the out-of-plane mirror symmetry, resulting in a switchable polarization with a saturated component of 0.089 pC/m and a low transition barrier of 28.8 meV per unit cell. Strikingly, low-concentration electrostatic doping enhances rather than suppresses the ferroelectric polarization due to the abnormal layer-dependent electronic occupation in BL-InSe, in contrast to the conventional screening paradigm. In addition, the characteristic Mexican-hat-shaped valence band enables doping-induced itinerant half-metallic ferromagnetism, where the interlayer spin density difference scales linearly with doping concentration and can be reversed by switching the polarization direction. These results demonstrate the coexistence of ferroelectric and ferromagnetic orders in BL-InSe and establish a viable platform for realizing voltage-tunable multiferroicity through stacking and carrier doping in otherwise nonpolar and nonmagnetic semiconductors.