Structural, electronic, and magnetic properties ofLaNi5−xTx(T=Fe,Mn)compounds

Abstract

Structures and magnetic properties of the ${\mathrm{LaNi}}_{5\ensuremath{-}x}{\mathrm{Fe}}_{x}$ and ${\mathrm{LaNi}}_{5\ensuremath{-}x}{\mathrm{Mn}}_{x}$ compounds have been investigated using neutron diffraction and first-principles tight-binding-linear-muffin-tin-orbital methods. Both neutron diffraction refinement data and total energy calculations show that the Fe and Mn atoms preferentially occupy the $3g$ sites in the hexagonal ${\mathrm{CaCu}}_{5}$-type structure. The calculated magnetic moments of Fe and Ni atoms are of $2.4--2.5{\ensuremath{\mu}}_{B}$ and $0.2--0.5{\ensuremath{\mu}}_{B}$ in ${\mathrm{LaNi}}_{5\ensuremath{-}x}{\mathrm{Fe}}_{x},$ respectively. The magnetic structure exhibits more localized moments at Fe atoms in ${\mathrm{LaNi}}_{5\ensuremath{-}x}{\mathrm{Fe}}_{x}$ when $x<~1.0.$ Electronic structure calculations indicate that s-conduction electron spin polarization from the Ni or La atoms strongly interacts with Fe(Mn) d-spin moments in ${\mathrm{LaNi}}_{5\ensuremath{-}x}\mathrm{Fe}(\mathrm{Mn}{)}_{x}$ $(x\ensuremath{\ne}0)$ compounds, which gives rise to a very large valence transferred hyperfine field on the Ni or La sites. This $s\ensuremath{-}d$ hybridization may lead to an interaction among magnetic clusters in these kinds of materials and may cause a spin freezing effect at low temperature when the Fe(Mn) content is very low in ${\mathrm{LaNi}}_{5\ensuremath{-}x}\mathrm{Fe}(\mathrm{Mn}{)}_{x}.$ Mn atoms show magnetic moments of $3.0{\ensuremath{\mu}}_{B}$ per atom due to a large exchange splitting in ${\mathrm{LaNi}}_{5\ensuremath{-}x}{\mathrm{Mn}}_{x}$ $(x\ensuremath{\ne}0).$ ${\mathrm{LaNi}}_{4}\mathrm{Mn}$ is found to be ferrimagnetic, whereas antiferromagnetic exchange coupling between the Mn atoms is preferred for ${\mathrm{LaNi}}_{3}{\mathrm{Mn}}_{2}.$ Both ferrimagnetic and ferromagnetic exchange interactions between Mn atoms are found in the ${\mathrm{LaNi}}_{2}{\mathrm{Mn}}_{3}$ compounds. The calculated results are in good agreement with the experimental neutron data.