Spin-glass behavior inCo3Mn3(O2BO3)2ludwigite with weak disorder

Abstract

X-ray diffraction, magnetization, ac susceptibility, and specific heat have been measured on high-quality single crystals of ${\mathrm{Co}}_{3}{\mathrm{Mn}}_{3}{({\mathrm{O}}_{2}{\mathrm{BO}}_{3})}_{2}$ ludwigite. Different from previously studied ludwigites, this compound is characterized by the existence two low-dimensional subunits each containing a unique ion. The subsystem formed by ions at sites 3-1-3, known as a three-legged ladder (3LL), contains only divalent Co ions, while the 3LL formed by ions at sites 4-2-4 contains both divalent and trivalent Mn ions. Although there is only a weak disorder caused by a very small amount of Mn at sites 1, the experimental results evidence the existence of a low-temperature spin-glass phase. A dynamic scaling analysis of ac susceptibility data according to conventional critical slowing down results in a spin-glass phase-transition temperature ${T}_{g}=31.9$ K and a dynamic exponent $z\ensuremath{\nu}=7.05$. The temperature dependence of heat capacity has a linear contribution with the coefficient $\ensuremath{\gamma}=21.9$ mJ/(mol ${\mathrm{K}}^{2}$), which shows that this compound has the highest degree of magnetic disorder among ludwigites, corroborating the spin-glass state at low temperatures. The origin of this state is discussed, taking into account the particular structure of each subunit and the competition between the different exchange interactions involved.