Formation of L1₀-FeNi hard magnetic material from FeNi-based amorphous alloys

Abstract

L10-FeNi hard magnetic alloy with coercivity reaching 861 Oe was synthesized through annealing Fe42Ni41.3Si8B4P4Cu0.7 amorphous alloy, and the L10-FeNi formation mechanism has been studied. It is found the L10-FeNi in annealed samples at 400 °C mainly originated from the residual amorphous phase during the second stage of crystallization which could take place over 60 °C lower than the measured onset temperature of the second stage with a 5 °C/min heating rate. Annealing at 400 °C after fully crystallization still caused a slight increase of coercivity, which was probably contributed by the limited transformation from other high temperature crystalline phases towards L10 phase, or the removal of B from L10 lattice and improvement of the ordering quality of L10 phase due to the reduced temperature from 520 °C to 400 °C. The first stage of crystallization has hardly direct contribution to L10-FeNi formation. Ab initio simulations show that the addition of Si or Co in L10-FeNi has the effect of enhancing the thermal stability of L10 phase without seriously deteriorating its magnetic hardness. The non-monotonic feature of direction dependent coercivity in ribbon segments resulted from the combination of domain wall pinning and demagnetization effects. The approaches of synthesizing L10-FeNi magnets by adding Si or Co and decreasing the onset crystallization temperature have been discussed in detail.

Accelerating Nature: Induced Atomic Order in Equiatomic FeNi

“…Notably, the materials of this current study do not contain large amounts of metalloid alloying additions, such as phosphorus and carbon, as were utilized in other works that reported synthesis of tetrataenite. [18,50,51] Preliminarily speaking, the combination of stress and magnetic field applied in-situ during thermal treatment has accomplished in 6 weeks what Nature requires millions of years to achieve. As the lattice diffusivity of the FeNi equiatomic composition has been reported as ≈1 × 10 −27 cm 2 s −1 at T = 573 K, [52] the process utilized in this work is estimated to accelerate diffusion by ten or more orders of magnitude.…”