Crystal structure and magnetism of $\mathrm{Co}_{2-x}\mathrm{Ni}_x\mathrm{B_2O_5}$ pyroborate

The high quality single crystals of $\mathrm{Co_2B_2O_5}$:$\mathrm{Ni}$ were synthesized. The detail study of crystal structure using single-crystal X-ray diffraction was carried out. The monoclinic symmetry was found ($\mathrm{P2_1/c}$ space group). The magnetization and magnetic susceptibility measurements have shown antiferromagnetic behavior below $T_N=47$ K and paramagnetic temperature $\theta=43$ K. The effective magnetic moment per magnetic ion was $3.49\,\mu_B$, which points out the divalent and high-spin state of $\mathrm{Co}$ and $\mathrm{Ni}$ ions.