Crystal and local atomic structure of MgFeBO₄ , Mg_0.5 Co_0.5 FeBO₄ and CoFeBO₄ : Effects of Co substitution

Abstract

Single‐crystalline MgFeBO4, Mg0.5Co0.5FeBO4, and CoFeBO4 have been grown by the flux method. The samples have been characterized by X‐ray spectral analysis, X‐ray diffraction, and X‐ray absorption spectroscopy. The X‐ray absorption near‐edge structure (XANES) and extended X‐ray absorption fine structure (EXAFS) spectra have been measured at the Fe and Co K‐edges over a wide temperature range (6.5–300 K). The composition, the charge state, and local environment of both Fe and Co atoms have been determined. The effects of Co substitution for Mg on the local structural distortions have been revealed experimentally and the MO bond anisotropy has been found.

Spin-glass behavior in single crystals of hetero-metallic magnetic warwickites MgFeBO4, Mg0.5Co0.5FeBO4, and CoFeBO4

“…The latter is found when competing interactions between the magnetic moments in a triangular lattice are effective. Previous structural analysis [25] clearly indicates the existence of atomic disorder in all three warwickites under investigation. In addition, several types of triangular motifs can be distinguished both inside the ribbon and between the adjacent ribbons (see Fig.…”

“…Both (M1 and M2) positions are occupied by a mixture of Mg, Co and Fe atoms, although trivalent Fe ions prefer smaller octahedra: M1O 6 in the Mg-Fe and Mg-Co-Fe warwickite, and M2O 6 one in the Co-Fe compound [25,24].…”

“…Detailed crystal data for Mg-Fe, Mg-Co-Fe and Co-Fe warwickites are obtained in a previous work [24] and summarized in Tables SMI and SMII of Supplementary Material [25]. The general features of the crystal structure are typical for warwickites [26].…”

“…SMI (b)). From the structural study on Mg-Fe, Mg-Co-Fe and Co-Fe warwickites [24] it may be inferred that Co and Mg enter into the warwickite structure with divalent state, and Fe with trivalent state. Both (M1 and M2) positions are occupied by a mixture of Mg, Co and Fe atoms, although trivalent Fe ions prefer smaller octahedra: M1O 6 in the Mg-Fe and Mg-Co-Fe warwickite, and M2O 6 one in the Co-Fe compound [24] [23].…”

Antiferromagnetism of the cation-ordered warwickite system Mn2-Mg BO4 (x = 0.5, 0.6 and 0.7)

“…From Fig. 14 where M = Ti 3+ [32], V 3+ [12], Fe 3+ [33], Sc 3+ [27], Ga 3+ [34], In 3+ [35], Ta 5+ [36] and Nb 5+ [36].…”