Specific heat and magnetization studies of ${\mathrm{Fe}}_2{\mathrm{OBO}}_3,$ ${\mathrm{Mn}}_2{\mathrm{OBO}}_3,$ and ${\mathrm{MgScOBO}}_3$

In this paper we report magnetic and specific heat results for the oxyborates ${\mathrm{Fe}}_2{\mathrm{OBO}}_3$ and ${\mathrm{Mn}}_2{\mathrm{OBO}}_3.$ The former presents L-type ferrimagnetism while the latter presents weak ferromagnetism in distinct ranges of temperature. The Curie constant for ${\mathrm{Mn}}_2{\mathrm{OBO}}_3$ is normal while that for ${\mathrm{Fe}}_2{\mathrm{OBO}}_3$ is unusually high, as a consequence of short-range ferromagnetic order. The specific heat of both systems at low temperatures is dominated by the magnetic excitations of the ordered magnetic phases. In order to subtract the lattice contribution to the specific heat in these systems, we measured the specific heat of the nearly isostructural, nonmagnetic compound ${\mathrm{MgScOBO}}_3.$ The remaining specific heat contains a magnetic part and an additional component associated with charge delocalization.