Exploration of new ferromagnetic, semiconducting and biocompatible Nb₃X₈(X = Cl, Br or I) monolayers with considerable visible and infrared light absorption

Abstract

Ferromagnetic character and biocompatible properties have become key factors for developing next-generation spintronic devices and show potential in biomedical applications. Unfortunately, the Mn-containing monolayer is not biocompatible though it has been extensively studied, and the Cr-containing monolayer is not environmental friendly, although these monolayers are ferromagnetic. Herein, we systematically investigated new types of 2D ferromagnetic monolayers Nb₃X₈ (X = Cl, Br or I) by means of first principles calculations together with mean field approximation based on the classical Heisenberg model. The small cleavage energy and high in-plane stiffness have been calculated to evaluate the feasibility of exfoliating the monolayers from their layered bulk phase. Spin-polarized calculations together with self-consistently determined Hubbard U were utilized to assess a strong correlation energy, which demonstrated that Nb₃X₈ (X = Cl, Br or I) monolayers are ferromagnetic. The calculated Curie temperatures for Nb₃Cl₈, Nb₃Br₈ and Nb₃I₈ were 31, 56 and 87 K, respectively, which may be increased by external strain, or electron or hole doping. Moreover, the Nb₃X₈ (X = Cl, Br or I) monolayers exhibited strong visible and infrared light absorption. The biocompatibility, ferromagnetism and considerable visible and infrared light absorption render the Nb₃X₈ (X = Cl, Br or I) monolayers with great potential application in next-generation biocompatible spintronic and optoelectronic devices.