Electronic structure and magnetic properties in $T_2\text{AlB}_2$ ($T$ = Fe, Mn, Cr, Co, and Ni) and their alloys

The electronic structure and intrinsic magnetic properties of $\text{Fe}_2\text{AlB}_2$-related compounds and their alloys have been investigated using density functional theory. For $\text{Fe}_2\text{AlB}_2$, the crystallographic $a$ axis is the easiest axis, which agrees with experiments. The magnetic ground state of $\text{Mn}_2\text{AlB}_2$ is found to be ferromagnetic in the basal $ab$ plane, but antiferromagnetic along the $c$ axis. All $3d$ dopings considered decrease the magnetization and Curie temperature in $\text{Fe}_2\text{AlB}_2$. Electron doping with Co or Ni has a stronger effect on the decreasing of Curie temperature in $\text{Fe}_2\text{AlB}_2$ than hole doping with Mn or Cr. However, a larger amount of Mn doping on $\text{Fe}_2\text{AlB}_2$ promotes the ferromagnetic to antiferromagnetic transition. A very anisotropic magnetoelastic effect is found in $\text{Fe}_2\text{AlB}_2$: the magnetization has a much stronger dependence on the lattice parameter $c$ than on $a$ or $b$, which is explained by electronic-structure features near the Fermi level. Dopings of other elements on B and Al sites are also discussed.