Specific features of magnetic properties of Tb$_{1-x}$Ho$_{x}$Al$_{3}$(BO$_{3}$)$_{4}$ aluminoborates

Single crystals Tb$_{1-x}$Ho$_{x}$Al$_{3}$(BO$_{3}$)$_{4}$ with $x$ = 0, 0.1, 0.5, 0.9, 1 have been grown based on bismuth trimolybdate using a solution–melt method. Their magnetic properties have been studied in the temperature range of 4.2–295 K and magnetic fields to 9 T. The effective magnetic moments $\mu_{\operatorname{eff}}\parallel$ and $\mu_{\operatorname{eff}}\perp$ have been determined. It has been found that the temperature dependence of the susceptibility measured experimentally differs from that calculated on the assumption that the contributions of Tb$^{3+}$ and Ho$^{3+}$ ions are proportional to fractions from the susceptibilities of TbAl$_{3}$(BO$_{3}$)$_{4}$ and HoAl$_{3}$(BO$_{3}$)$_{4}$, respectively.