Abstract-We report on the thermodynamic, magnetic properties and the magnetic structure of ludwigite-type Cu 2 MnBO 5 . The specific heat, the low-field magnetization and the paramagnetic susceptibility were studied on a single crystal and combined with powder neutron diffraction data. The temperature dependence of the specific heat and the neutron diffraction pattern reveal a single magnetic phase transition at T=92 K, which corresponds to the magnetic ordering into a ferromagnetic phase. The cation distribution and the values and directions of magnetic moments of ions in different crystallographic sites are established. The magnetic moments of Cu 2+ and Mn 3+ ions occupying different magnetic sites in the ferrimagnetic phase are pairwise antiparallel and their directions do not coincide with the directions of the principal crystallographic axes.The small value of the magnetic moment of copper ions occupying site 2a is indicative of partial disordering of the magnetic moments on this site. The magnetization measurements show a strong temperature hysteresis of magnetization, which evidences for field-dependent transitions below the phase transition temperature.

Single crystals of ludwigite Ni 2 MnBO 5 were synthesized by flux growth technique. The detailed structural and magnetic characterizations of the synthesized samples have been carried out. The cations composition of the studied crystal was determined using X-ray diffraction and EXAFS technique, the resulting composition is differ from the content of the initial Mn 2 O 3 -CuO components of flux. Magnetic susceptibility measurements and the calculations of the exchange integrals in frameworks of indirect coupling model revealed strong antiferromagnetic interactions and appearance of magnetic ordering phase at the temperature T=85 K. The hypothesis of the existence of several magnetic subsystems was supposed.

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