Theoretical investigation into the possibility of very large moments in Fe16N2

Abstract

We examine the mystery of the disputed high-magnetization α ′′ -Fe16N2 phase, employing the Heyd-Scuseria-Ernzerhof screened hybrid functional method, perturbative many-body corrections through the GW approximation, and onsite Coulomb correlations through the GGA+U method. We present a first-principles computation of the effective on-site Coulomb interaction (Hubbard U ) between localized 3d electrons employing the constrained random-phase approximation (cRPA), finding only somewhat stronger on-site correlations than in bcc Fe. We find that the hybrid functional method, the GW approximation, and the GGA+U method (using parameters computed from cRPA) yield an average spin moment of 2.9, 2.6 -2.7, and 2.7 µB per Fe, respectively.

A review of high magnetic moment thin films for microscale and nanotechnology applications

“…292,293 The mixed nature of the FeN compounds, which makes it very hard to actually (quantitatively) determine the a 00 thicker layers or foils, 294 and also the limited thickness of MBE-grown samples impacting on the accuracy of saturation magnetisation measurements, still keep the error bars on measured magnetisation values unpleasantly large. First theoretical explanation attempts for a saturation moment beyond the Slater-Pauling limit were given by Ji et al 285,295 based on partially localised electron states due to the octahedral structure of FeN clusters in a 00 Fe 16 N 2 (see also Sims et al 296 and Shi et al 297 ); however, XMCD measurements which were supposed to corroborate the claim did only confirm that there are increased-moment Fe sites in ordered Fe 16 N 2 and disordered Fe 8 N crystals alike. 298 In a 2013 study, Ji et al 299 however, no significant magnetisation since the overall a 00 phase content was only 22% after annealing.…”

Effects of alloying and strain on the magnetic properties of Fe16N2

“…7 A new way to prepare single-phase Fe 16 N 2 powder was recently reported, along with evidence of high maximum energy product (BH max ). 8 Most theoretical studies of the magnetization of α -Fe 16 N 2 were performed using the local density approximation, generalized gradient approximation (GGA), or LDA + U , though recently Sims et al 9 applied a hybrid functional and the GW approximation to this material. In LDA or GGA the magnetic moment of Fe 16 N 2 is only slightly enhanced compared to elemental Fe.…”

Large magnetic anisotropy predicted for rare-earth-free Fe16−xCoxN2Zhao1, Wang2, Yao3 et al. 2016Phys. Rev. B494170View full textAdd to dashboardCite

“…Because of the promising magnetic properties observed in thin films, efforts to synthesize bulk samples of the tetragonal -Fe 16 N 2 phase have also been made. [8][9][10] In the -Fe 16 N 2 structure, the body-centered cubic (bcc) Fe lattice is expanded into a distorted body-centered tetragonal (bct) lattice due to the presence of N. Close to 500 K, the tetragonal -Fe 16 Nevertheless, the calculations were done using the -Fe 16 N 2 structure and the effect of transition metals (TM) substitution on the crystal structures and phase stabilities has not been investigated.…”

“…1(d), the phonon density-ofstates of these three structures are plotted. The phonon calculation was performed using a supercell approach by the Phonopy code, 25 where supercells with sizes of 324 atoms for Fe 16 Based on the results from our AGA search, the lowest-energy structure of Co 16 N 2 is cubic rather than tetragonal. In Fig.…”