Inspired by nature: investigating tetrataenite for permanent magnet applications

Abstract

Chemically ordered L10-type FeNi, also known as tetrataenite, is under investigation as a rare-earth-free advanced permanent magnet. Correlations between crystal structure, microstructure and magnetic properties of naturally occurring tetrataenite with a slightly Fe-rich composition (~ Fe55Ni44) obtained from the meteorite NWA 6259 are reported and augmented with computationally derived results. The tetrataenite microstructure exhibits three mutually orthogonal crystallographic variants of the L10 structure that reduce its remanence; nonetheless, even in its highly unoptimized state tetrataenite provides a room-temperature coercivity of 95.5 kA m(-1) (1200 Oe), a Curie temperature of at least 830 K and a largely temperature-independent anisotropy that preliminarily point to a theoretical magnetic energy product exceeding (BH)max = 335 kJ m(-3) (42 MG Oe) and approaching those found in today's best rare-earth-based magnets.

Crystallization induced ordering of hard magnetic L1 phase in melt-spun FeNi-based ribbons

“…2,7 Therefore, the ordered phase of FeNi has drawn renewed attention as a novel alternate to rare earth based permanent magnets. [8][9][10][11] The theoretical maximum magnetic energy product of L1 0 FeNi (∼42 MGOe) is close to that of the currently available best hard magnets. 10,11 It is to be noted that the tetrataenite (L1 0 FeNi phase) was formed during extremely slow cooling of billions of years in the universe.…”

“…[8][9][10][11] The theoretical maximum magnetic energy product of L1 0 FeNi (∼42 MGOe) is close to that of the currently available best hard magnets. 10,11 It is to be noted that the tetrataenite (L1 0 FeNi phase) was formed during extremely slow cooling of billions of years in the universe. 8 A brief history of the investigation on tetrataenite has been reviewed in the literature.…”

“…8 A brief history of the investigation on tetrataenite has been reviewed in the literature. 10,12 However, the production of the ordered phase is practically difficult since the order-disorder transition temperature of this alloy was reported to be as low as 593 K. 2 Mobility of atoms is extremely low below the transition temperature.…”

Intrinsic magnetic properties of L1 FeNi obtained from meteorite NWA 6259

“…% Ni, near the Fe-rich end of the L1 0 phase field. 13 Our previous studies of NWA 6259 have confirmed via transmission electron microscopy (TEM) the presence of L1 0 FeNi with at least two variants of the c-axis orientation, correlated the intrinsic magnetic properties with the microstructure of bulk tetrataenite, 14 and revealed the extraordinary temperature stability of the magnetic properties. 15 In the latter paper, hard-direction magnetization data were used to estimate the anisotropy field of the NWA 6259 tetrataenite as H a ¼ 20 6 3 kOe, most likely toward the lower end of the range ($17 kOe).…”

“…Mo k a x-ray diffraction (XRD) and electron back-scatter diffraction (EBSD) were conducted on a polished surface of the cylinder to determine texture and crystallographic orientation, as previously reported. 14 Hysteresis loops were measured using a LakeShore Model 7410 vibrating sample magnetometer (VSM). The large mass of the cylinder proved problematical for magnetic measurements with the VSM; at applied fields greater than 15 kOe, the small magnetic field gradients in the electromagnet caused a deflection of the sample at the end of its mounting rod, creating spurious moment readings.…”