Magnetism and specific heat of ludwigites Mn1.17Co1.83BO5 and Mn1.39Co1.61BO5

https://doi.org/10.1016/j.jallcom.2023.173143

Mn_1.17Co_1.83BO₅ and Mn_1.39Co_1.61BO₅ ludwigites were synthesized by the flux technique and investigated by means of X-ray diffraction, X-ray fluorescence, DC and AC magnetic susceptibility, and specific heat analysis. The crystal structure of both ludwigites belongs to the Pbam space group with a = 9.25 Å, b = 12.41 Å, and c = 3.05 Å for Mn_1.17Co_1.83BO₅ and a = 9.27 Å, b = 12.45 Å, and c = 3.05 Å for Mn_1.39Co_1.61BO₅. The simultaneously observed negative values of the Curie-Weiss temperatures and ferromagnetic-type hysteresis loops allow us to assume that the ferrimagnetic ordering is realized in Mn_1.39Co_1.61BO₅ below T_F = 60.8 K, while in Mn_1.17Co_1.83BO₅ in addition to the above mentioned experimental facts the frequency dependencies of the real and imaginary parts of the AC magnetization were observed assuming the presence of the canonical spin-glass state below T_SG = 44.5 K. The observed difference in coercive forces of M-H curves at low temperatures can be associated with presence of two spin subsystems for Mn_1.17Co_1.83BO₅.