We study the behavior of the Cr${}_{2+x}$Se alloys based on state-of-the-art first-principles electronic structure calculations. We show that these alloys are of special interest since they combine possible applications in spintronics devices with a series of diverse magnetic phenomena. First, we show that Cr${}_2$Se prefers the C1${}_b$ structure while Cr${}_3$Se crystallizes in the D0${}_3$ lattice. Our calculations suggest that as we dope Cr${}_2$Se with Cr atoms and move towards Cr${}_3$Se, all alloys are half-metallic fully compensated ferrimagnets (also known as half-metallic antiferromagnets) with a gap in the spin-down band. All alloys follow a generalized version of the Slater-Pauling rule for the Heusler compounds and we show that for Cr${}_3$Se a small deviation occurs due to the antibonding single band created by the 4$s$ states of the Cr and Se atoms in the spin-down band structure which crosses the Fermi level. In the case of Cr${}_3$Se we observe a metamagnetic behavior under hydrostatic pressure since Cr atoms with different symmetry present both itinerant and localized magnetic properties. Finally, calculations based on the frozen-magnon approximation reveal that the strong intersublattice antiferromagnetic coupling between the nearest-neighboring Cr atoms stabilizes the ferrimagnetic character of both Cr${}_2$Se and Cr${}_3$Se and leads to estimated Curie temperature exceeding considerably the room temperature. Combination of this feature together with the half-metallic antiferromagnetism makes the Cr${}_{2+x}$Se alloys ideal for realistic spintronics applications.

• Received 10 August 2012

DOI:https://doi.org/10.1103/PhysRevB.86.134427