Mössbauer study of A-site ordered spinel LiFeCr₄O₈

⁵⁷Fe Mössbauer spectroscopy of the A-site ordered spinel LiFeCr₄O₈ has been conducted in order to investigate the local structure and magnetic structure. The paramagnetic spectrum is composed of a singlet, reflecting the cubic local symmetry. Below T_N ≈ 94 K, the spectrum becomes a very broad hyperfine sextet, which is interpreted as a distribution of the hyperfine field. The arrangement of the half-filled A-site Fe ions and the breathing pyrochlore Cr ions may produce a wide distribution in the magnetic interaction. Below T_MS ≈ 23 K, the spectral shape abruptly changes to a well-resolved sextet, which can be fitted by one component sextet with a very small quadrupole shift. We found that the high-temperature magnetic phase (ferrimagnetic) and the low-temperature magnetic phase (conical) coexist even at 40 K. The spin-gap transition around T_SG ≈ 60 K is not observed. The reported decrease in the magnetization below around 50 K may be a result of increasing magnetic anisotropy due to the appearance of the conical magnetic phase.