The electric and magnetic properties of novel two-dimensional H and T' Phase GdX2 (X = F, Cl, Br, I) from first-principles calculations

Two-dimensional rare-earth metal halides with large 4f magnetic moments have been found multiferroic with ferromagnetism, ferroelectricity and ferroelasticity. First-principles calculations within density functional theory are carried out to investigate the structural, electronic, and magnetic properties of novel two-dimensional rare earth metal halides GdX2 (X = F, Cl, Br, I), herein, both H and T' phase structures are studied. The calculated phonon dispersion relationships indicate that H phase structures are dynamically stable, while the T' phase GdCl2 GdBr2 and GdI2 can exist as freestanding monolayers. The HSE06 hybrid functional theory combing spin-orbit coupling correction is employed to discover that all four H phase structures and three T' phase structures harbor the conductive behavior of semiconductors. Based on the calculated exchange interactions and magnetocrystalline anisotropy intensities, Curie temperatures of ferromagnetic H phase GdX2 between 323 and 392 K are predicted by Monte Carlo simulations, while Curie temperature of T' phase GdI2 is about 111 K. However, T' phase GdCl2 and GdBr2 exhibit stripe-like antiferromagnetic ground states with Neel temperatures of about 76 and 63 K.