Silver hollandite ( AgxMn8O16 , x≤2 ): A highly anisotropic half-metal for spintronics

Structural, electronic, and magnetic properties of a crystalline material formed by parallel chains of silver atoms inside the tunnels of a manganese dioxide host with the hollandite structure, ${\mathrm{Ag}}_x{\mathrm{Mn}}₈{\mathrm{O}}₁₆$, are studied with density functional theory (DFT) calculations. More magnetic structures were studied, including ferromagnetic (FM) and C2 antiferromagnetic (C2-AFM) orderings on Mn atoms of pristine hollandite ${\mathrm{Mn}}₈{\mathrm{O}}₁₆$ and the FM state of ${\mathrm{Ag}}_x{\mathrm{Mn}}₈{\mathrm{O}}₁₆$. Thereby, Hubbard corrections and different values for the Ag content, $x\ensuremath{\le}2$, were considered. The results show that hollandite ${\mathrm{Mn}}₈{\mathrm{O}}₁₆$ is a semiconducting oxide both in the FM and in the AFM states, but with the C2-AFM configuration as the ground state. Interestingly, for the FM state of ${\mathrm{Ag}}_x{\mathrm{Mn}}₈{\mathrm{O}}₁₆$ for high silver content, $x=2$, the system is a perfect and isotropic half-metal, but when not all tunnels are filled with Ag chains, i.e., for $x<2$, it behaves as a quasi-one-dimensional system retaining the perfect half-metallicity. The results demonstrate that the incorporation of the monoatomic Ag chains inside the hollandite ${\mathrm{Mn}}₈{\mathrm{O}}₁₆$ host leads to a stable system that can be used as a spin filter for instance for spintronics devices.