Tuning the Magnetocrystalline Anisotropy of Rare-Earth Free L10-Ordered Mn1-Xtmxal Magnetic

Abstract

L 1 0 -ordered MnAl (τ-phase) alloy is ferromagnetic and possesses a reasonably high magnetocrystalline anisotropy energy; therefore, a good candidate for a rare-earth-free permanent magnet.  Tuning of the magnetocrystalline anisotropy was studied by substituting Mn of MnAl with transition element (Fe, Co, or Ni). First-principles calculations based on density functional theory (DFT) were performed, as implemented in the WIEN2k, to calculate the electronic structures of Mn 0.5 TM 0.5 Al, where TM = Mn, Fe, Co, and Ni.  The calculated total magnetic moment of Mn 0.5 TM 0.5 Al decreases as the number of valence electrons ( n ) of TM (e.g., 7 for Mn (3 d 5 4 s 2 ), 8 for Fe (3 d 6 4 s 2 ), 9 for Co (3 d 7 4 s 2 ), and 10 for Ni (3 d 8 4 s 2 )) increases. It was found that Ni-substituted MnAl becomes ferrimagnetic, while other TM substituted MnAl retain a ferromagnetic state. Curie temperature rapidly decreases with increasing the valence electrons from 685 K for MnAl to 20 K for Ni-substituted MnAl. Thermomagnetic behaviors of Mn 0.5 TM 0.5 Al (TM = Mn, Fe, Co, or Ni) are reported.The calculated magnetocrystalline anisotropy constant ( K ) of Mn 0.5 TM 0.5 Al is1.34 MJ/m 3 for TM = Mn, 2.98 MJ/m 3 for TM = Fe, -0.30 MJ/m 3 for TM = Co, and -0.18 MJ/m 3 for Ni.  Our magnetocrystalline anisotropy energy (MAE) calculations confirm that the magnetocrystalline anisotropy changes to the out-of-plane (uniaxial) direction from the in-plane for Co- and Ni-substituted MnAl.  The K reaches a maximum of 2.98 MJ/m 3 at n = 8, i.e. , Fe substitution.

Keywords: First-principles calculations, Hard magnetic material, Magnetic properties, L10-ordered structure