Tuning the magnetocrystalline anisotropy ofFe3Snby alloying

Abstract

The electronic structure, magnetic properties and phase formation of hexagonal ferromagnetic Fe 3 Sn-based alloys have been studied from first principles and by experiment. The pristine Fe 3 Sn compound is known to fulfill all the requirements for a good permanent magnet, except for the magnetocrystalline anisotropy energy (MAE). The latter is large, but planar, i.e. the easy magnetization axis is not along the hexagonal c direction, whereas a good permanent magnet requires the MAE to be uniaxial. Here we consider Fe 3 Sn 0.75 M 0.25 , where M= Si, P, Ga, Ge, As, Se, In, Sb, Te and Bi, and show how different dopants on the Sn sublattice affect the MAE and can alter it from planar to uniaxial. The stability of the doped Fe 3 Sn phases is elucidated theoretically via the calculations of their formation enthalpies. A micromagnetic model is developed in order to estimate the energy density product (BH) max and coercive field µ 0 H c of a potential magnet made of Fe 3 Sn 0.75 Sb 0.25 , the most promising candidate from theoretical studies. The phase stability and magnetic properties of the Fe 3 Sn compound doped with Sb and Mn has been checked experimentally on the samples synthesised using the reactive crucible melting technique as well as by solid state reaction. The Fe 3 Sn-Sb compound is found to be stable when alloyed with Mn. It is shown that even small structural changes, such as a change of the c/a ratio or volume, that can be induced by, e.g., alloying with Mn, can influence anisotropy and reverse it from planar to uniaxial and back.

Density functional prediction of the structural, elastic, electronic, and thermodynamic properties of the cubic and hexagonal (c, h)-Fe2Hf

“…DFT is a general-purpose computational method and can be applied to most x systems. Although density functional theory is more accurate and exact in theory, its implementation requires several approximations such as the choice of basis-set, exchange-correlation [9][10][11] functional, mesh-size for Brillouin zone [12][13][14] for planewave basis.…”

Computational Design of Rare-Earth Reduced Permanent Magnets

“…Attempts to stabilize the phase by small additions of Mn were successful. However, owing to the change of the electronic structure and the number of valence electrons the anisotropy flipped back to in-plane again [22].…”

“…Right hand side: At an internal field of µ0Hint = 0.49 T the flower like magnetic state (1) breaks into a two-domain state (2) with a domain wall pinned at the grain boundaries. Images reproduced from[22].…”

Synergistic computational and experimental discovery of novel magnetic materials

“…Similarly, Fe 3 Sn forms Ni 2 In-type hexagonal structure with a = 5.46 Å and c = 3.35 Å, and shows an easy-plane anisotropy K 1 = -18 Mergs/cm 3 , J s = 14.8 kG, and T c = 725 K. 68 DFT calculations and experiments also revealed that the alloying with a third element such as Sb can alter the anisotropy from easy plane (-ve K 1 ) in Fe 3 Sn to easy axis (+ve K 1 ) in Fe 3 Sn 0.75 Sb 0.25 . 68,71…”