Large Orbital Moments and Internal Magnetic Fields in Lithium Nitridoferrate(I)

Abstract

The iron nitridometalates Li2[(Li(1-x)Fe(I)(x))N] display ferromagnetic ordering and spin freezing. Large magnetic moments up to 5.0mu(B)/Fe are found in the magnetization. In Mössbauer effect studies huge hyperfine magnetic fields up to 696 kOe are observed at specific Fe sites. These extraordinary fields and moments originate in an unusual ligand field splitting for those Fe species leading [within local spin density approximation (LSDA)] to a localized orbitally degenerate doublet. Including spin-orbit interaction and strong intra-atomic electron correlation (LDA+SO+U) gives rise to a large orbital momentum.

Giant magnetic anisotropy and tunnelling of the magnetization in Li2(Li1−xFex)N

“…1d). Structural parameters and selected x values were determined by singlecrystal and powder X-ray diffraction and are in good agreement with earlier results 22,[27][28][29] . To support our findings we present details of crystal growth procedure and chemical analysis (see Methods), as well as X-ray powder diffraction (Supplementary Fig.…”

“…The inverse magnetic susceptibility, w À 1 ¼ H/M, roughly follows a Curie-Weiss behaviour for T\150 K and is strongly anisotropic over the whole investigated temperature range (Fig. 2c) 22,24).…”

“…4f) indicates that the slow relaxation leads to magnetic hysteresis for xo o1, that is, the dilute system is not a ferromagnet and hysteresis emerges from a slow decay of a polarized, paramagnetic state. Whether this holds true for the dense system (x ¼ 0.28), too, is not settled at this point-below TE65 K the ordering appears to be static on the timescale of Mössbauer spectroscopy 22,23 (performed on polycrystalline material, x ¼ 0.16 and 0.21). A possible schematic for the magnetic moment orientation and the magnetic anisotropy energy is depicted in Fig.…”

“…The absence of an orbital contribution is reflected, for example, in the largely isotropic magnetization of the elemental ferromagnets Fe, Co and Ni 20,21 . However, Klatyk et al 22 have suggested that a rare interplay of crystal electric field effects and spin-orbit coupling causes a large orbital contribution to the magnetic moment of Fe in polycrystalline Li 2 (Li 1-x Fe x )N. On the basis of the strong increase of the magnetization on cooling 22 and on Mössbauer spectroscopy 22,23 , a ferromagnetic ordering with T C E65 K was inferred for x ¼ 0.21 and, furthermore, huge hyperfine fields were found. The orbital contribution to the magnetic moment of Fe as well as the large hyperfine fields were theoretically described within the framework of local density approximation (LDA) calculations 22,24 .…”

“…The orbital contribution to the magnetic moment of Fe as well as the large hyperfine fields were theoretically described within the framework of local density approximation (LDA) calculations 22,24 . Furthermore, a large magnetic anisotropy has been theoretically proposed 22,24 .…”