Magnetism ofGd5Ge4from first principles

Abstract

The origin of ferromagnetism appearing as a result of a magnetic-field-induced first-order phase transition in ${\mathrm{Gd}}_{5}{\mathrm{Ge}}_{4}$ is explored by calculating the total energy, local exchange splitting, density of states, and magnetic moments. The calculations were performed using the tight-binding linear muffin-tin orbital method within the nonlocal exchange correlation parametrization in the density functional theory including the on-site Coulomb interaction parameter. The total energy as a function of shear distortion along the $a$ axis for two different orthorhombic structures is in agreement with experiment, indicating a first-order magnetostructural transition in ${\mathrm{Gd}}_{5}{\mathrm{Ge}}_{4}$. The rearrangement of Gd $5d$ and Ge $4p$ densities of states, the substantial differences in atom-projected band energies, the exchange splitting, and the magnetic moments calculated with ferromagnetic spin arrangements in the orthorhombic ${\mathrm{Sm}}_{5}{\mathrm{Ge}}_{4}$-type and ${\mathrm{Gd}}_{5}{\mathrm{Si}}_{4}$-type structures of ${\mathrm{Gd}}_{5}{\mathrm{Ge}}_{4}$ help to clarify the differences in the magnetic states of these two structures. Our calculations indicate that the ${\mathrm{Sm}}_{5}{\mathrm{Ge}}_{4}$-type structure of ${\mathrm{Gd}}_{5}{\mathrm{Ge}}_{4}$ is the structural ground state and that it is antiferromagnetic.