Microscopic evidence of magnetic and structure phase transition in multiferroic spinel FeV2O4

We report the microscopic evidence for magnetic and structural phase transitions in multiferroic spinel FeV2O4 from the hyperfine magnetic interaction. FeV2O4 sample shows three different crystal structures with the phase transitions from tetragonal to orthorhombic structure around 70 K, from orthorhombic to tetragonal structure around 109 K, and from tetragonal to cubic structure around 140 K. Mossbauer spectra of FeV2O4, obtained at various temperatures, were analyzed with severely distorted 8-line below T-C, and doublet at T-C. Also, the Mossbauer spectra change from doublet to singlet around T-JT congruent to 140 K due to the reduction of Jahn-Teller effect. The value of electric quadrupole splitting (Delta E-Q) is 3.05 mm/s at 4.2 K, indicating the noncollinear spin structure with strong polarization from the gap energy of (5)T(2)g band, Delta(1) congruent to 0. Whereas, there is collinear spin structure between T-S congruent to 70 K < T < TC congruent to 109 K, since Delta(1) in this temperature range increases from the value when T < T-S due to the non-degenerate energy state with commensuration in the collinear state. Also, we have found that large polar angle theta for T < T-S suggests the spin of the Fe2+ cations aligns along c-axis with the distortion in the a-b plane, while the small azimuthal angle theta suggest the direction of the spin is within ab-plane for T-S < T < T-C. (C) 2017 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).