Synthesis ofα′′−Fe16N2Compound Anisotropic Magnet by

Abstract

α"-Fe 16 N 2 is considered as one of the most promising candidates for future rare-earth-free magnets, showing the highest saturation magnetization reported so far. We propose and demonstrate a novel "strained wire method" to synthesize α˝-Fe 16 N 2 compound anisotropic magnets with enhanced hard magnetic property, with a direct experimental observation of the inter-coupling between tensile strain and the martensitic phase transition. The principal is helpful for the generation of other martensitic phase. In this paper, the method is demonstrated on an α"-Fe 16 N 2 compound permanent magnet preparation by starting from pure bulk iron, with urea as the nitrogen provider. A uniaxial tensile stress is applied on the wire-shaped sample during the post-annealing stage, producing a promising permanent magnet with hard magnet property which lacks any rare-earth elements. The sample synthesized in the lab exhibits coercivity of 1220 Oe and an energy product of up to 9 MGOe. The mechanism of the strained wire method is analyzed based on Scanning Transmission Electron Microscopy (STEM) characterizations of samples with different strains. This is the first time a straininduced recrystallization of α"-Fe 16 N 2 samples at low annealing temperature (150 ºC) has been observed. We demonstrate that this strained wire method can be used on α"-Fe 16 N 2 samples to increase the α"-Fe 16 N 2 phase-volume ratio and to fine tune its microstructure at low temperature. Some further characterization results are also included in this paper. The physics of the influence of tensile stress on the martensitic phase transition is discussed.

Martensitic αʺ-Fe16N2-Type Phase of Non-Stoichiometric Composition: Current Status of Research and Microscopic Statistical-Thermodynamic Model

“…there are also several other methods to prepare α″Fe 16 N 2 . they are as follow: the molecular beam epitaxy [31,32], the ion implantation [33][34][35] and beam deposition [36,37], the facing target [38][39][40] and reactive (magnetron) [41][42][43] sputtering, the ball milling [44], and so called 'strainedwire method' [1,45] when a uniaxial tensile stress is applied on the wireshaped sample during the postannealing stage.…”

Innovative Method for the Mass Preparation of α″-Fe16N2 Powders via Gas Atomization

“…After the first report by Kim and Takahashi on the giant saturation magnetization of about 290 emu/g of the α -Fe 16 N 2 phase in the evaporated Fe-N thin film, many researchers have made sustained efforts on both the fundamental [8,9] and practical aspects of preparing of the α -Fe 16 N 2 material. Thus, several attempts have been successfully made to develop magnetic materials containing α -Fe 16 N 2 phase in the form of thin films [10][11][12][13], foils [14,15], rods [16], ribbons [17], nanocones [18], and nanoparticles and powders [19,20], by using different preparation methods. The reported values of saturation magnetizations were widely scattered from 230 to 315 emu/g and appeared to be inconsistent and sometimes contradictory.…”

Structure and magnetic properties IN the mixture of Fe and BN powders after high-energy ball milling and annealing

“…It is suggested the BN powder to be as a candidate for new-phase production [6][7][8]. One of approaches to obtain iron nitrides is the solid-state reactions by mechanical activation milling (mechanical alloying, MA) a mixture of Fe and h-BN [9][10][11][12][13] or Fe and NH4NO3 [14][15][16][17].…”