Magnetic Interactions and Band Gaps of the (CrO₂)₂/(MgH₂) _n Superlattices

Abstract

Superlattices constructed with different materials such as ferromagnets and insulators at atomic scale provide an ideal platform for exploring many emergent physical phenomena. In the present work, a new type of superlattices composed of ferromagnetic half-metal CrO$_2$, with a thickness of two atomic layers, together with insulating MgH$_2$ has been constructed. Systematic theoretical studies on the (CrO$_2$)$_2$/(MgH$_2$)$_n$ ($n = 2, 3, 4, 5, 6$) superlattices are carried out based on first-principles density-functional theory calculations. These superlattices are ferromagnetic semiconductors with similar intra-layer magnetic exchange couplings between Cr ions. As the thickness of the MgH$_2$ layer increases, the magnetic exchange interaction between inter-layer Cr ions show an oscillating decaying behavior, while the energy band gaps show a small increase. The understanding of magnetic couplings in these superlattices provides a pathway for constructing new ferromagnetic semiconductors.