Abstract
A novel synthesis approach is developed to prepare nanocrystalline γ’-Fe4N in this paper. High energy cryomilling approach in liquid nitrogen is used to prepare the sample. A FexN amorphous state with a degree of metastable supersaturation of N into Fe is obtained. The crystalline size after higher energy cryomilling approach is characterized to be 40 ∼ 80 nm. A post-annealing among 200 ∼ 300 °C for 10 minutes results in phase transformation from α-iron into γ’-Fe4N. Its magnetic properties and structures are characterized, showing good soft magnetic material with ultralow coercivity (0.7 Oe). It shows high electrical resistivity (375 μΩ·m) at room temperature. The feasibility of the ball milling synthesis approach in liquid nitrogen is verified, suggesting a novel approach for the soft magnetic material preparation.
Highlights
Iron-nitrogen system is composed of earth-abundant and nontoxic elements
It is very interesting that the other iron-nitrogen phase, γ’Fe4N, with a cubic anti-perovskite structure and 20 at.% N located at the body center position of face-centered cubic Fe, shows good soft magnetic materials
Further improvement on the annealing temperature, above 300 ○C shows no obvious influence on the X-Ray Diffraction (XRD) peaks anymore
Summary
Iron-nitrogen system is composed of earth-abundant and nontoxic elements. The system includes several kinds of phases demonstrating strong ferromagnetism, including γ’-Fe4N, α”-Fe16N2 and ε-Fe3N.1. The phase of α”-Fe16N2, with body-centertetragonal (bct) crystalline structure, exhibits super-strong hard magnetic properties experimentally, showing the possibility of taking the place of the rare-earth permanent magnet.. It is very interesting that the other iron-nitrogen phase, γ’Fe4N, with a cubic anti-perovskite structure and 20 at.% N located at the body center position of face-centered cubic (fcc) Fe, shows good soft magnetic materials. Experiment results demonstrate its low coercivity with high permeability and reasonable high saturation magnetization.. For the practical application as transformer core, its property of large electrical resistivity is very helpful for the efficiency of the power transmission.. The Curie temperature of γ’-Fe4N is reported to be 767 K.6 Experiment results demonstrate its low coercivity with high permeability and reasonable high saturation magnetization. For the practical application as transformer core, its property of large electrical resistivity is very helpful for the efficiency of the power transmission. The Curie temperature of γ’-Fe4N is reported to be 767 K.6
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