Revisiting Neel 60 years on

The magnetocrystalline anisotropy energy of atomically ordered L1₀ FeNi (the meteoritic mineral tetrataenite) is studied in this paper* (authored by Dr Chris Patrick, the University of Warwick and Northeastern University, Boston) within a first-principles electronic structure framework.

Two compositions are examined: equiatomic Fe_0.5 Ni_0.5 and a Fe-rich composition, Fe_0.56Ni_0.44.  The paper confirms that, for the single crystals modeled the leading-order anistropy coefficient K₁ dominates the higher-order coefficients K₂ and K₃.  

To enable comparison with experiment , the effects of both imperfect atomic long-range order and finite temperature were included.  The authors' computational results initially appeared to undershoot the measured experimental values for the system, but careful scrutiny of the original analysis due to Neel et all suggested that their computed value of K₁ was in fact consistent with experimental values, and that the noted discrepancy had its origins in the nanoscale polycrystalline, multivariant nature of experimental samples, which yield much larger values of K₂ and K₃ than expected a priori.

The results provide fresh insight into the existing discrepancies in the literature regarding the value of tetrataenite's uniaxial magnetocrystalline anisotropy in both natural and synthetic values.

* 'Revisiting Neel 60 years on: the magnetic anisotropy of L1₀ FeNi (tetrataenite)', published in Journal of Applied Physics.