Magnetic and structural properties of ferromagnetic Fe5PB2 and Fe5SiB2 and effects of Co and Mn substitutions

TL;DR

This study investigates the crystallographic and magnetic properties of Fe5PB2, Fe5SiB2, and their Co and Mn substituted variants, revealing effects on magnetic moments, anisotropy, and thermal expansion through experimental and first-principles methods.

Contribution

It provides new insights into how Co and Mn substitutions affect the magnetic and structural properties of Fe5PB2 and Fe5SiB2, including magnetic moments, anisotropy, and thermal expansion behavior.

Findings

Cobalt reduces Curie temperature by over 100 K and magnetic moments by 16-20%.

Manganese has a smaller impact on magnetic properties.

First-principles calculations agree with experimental results.

Abstract

Crystallographic and magnetic properties of Fe5PB2, Fe4CoPB2, Fe4MnPB2, Fe5SiB2, Fe4CoSiB2, and Fe4MnSiB2 are reported. All adopt the tetragonal Cr5B3 structure-type and are ferromagnetic at room temperature with easy axis of magnetization along the c-axis. The spin reorientation in Fe5SiB2 is observed as an anomaly in the magnetization near 170 K, and is suppressed by substitution of Co or Mn for Fe. The silicides are found to generally have larger magnetic moments than the phosphides, but the data suggests smaller magnetic anisotropy in the silicides. Cobalt substitution reduces the Curie temperatures by more than 100 K and ordered magnetic moments by 16-20%, while manganese substitution has a much smaller effect. This suggests Mn moments align ferromagnetically with the Fe and that Co does not have an ordered moment in these structures. Anisotropic thermal expansion is observed in Fe5PB2 and Fe5SiB2, with negative thermal expansion seen along the c-axis of Fe5SiB2. First principles calculations of the magnetic properties of Fe5SiB2 and Fe4MnSiB2 are reported. The results, including the magnetic moment and anisotropy, and are in good agreement with experiment.