A study of the magnetic, thermal, and optical absorption properties in Ho(OH)3 crystal

This paper reports the result of our experimental study on the mean susceptibilities $\mathrm{K̄}$ and also the molar anisotropies K_∥–K_⊥ between 300 and 80 K in pure Ho(OH)₃ crystals. In our previous study we had shown that for Ho³⁺ compounds having C_3h symmetry, the thermal variation of the magnetic anisotropies from 300–80 K are sensitively dependent on the detailed pattern of the crystal‐field levels of the lowest ⁵I₈ term, i.e., on the crystal‐field parameters (CFP). Thus by fitting the experimental results of $\mathrm{K̄}$ , K_∥–K_⊥, K_∥ and K_⊥ K_⊥ simultaneously in the temperature region studied, we determined the CFP for Ho(OH)₃ more accurately than was possible from an analysis of spectral data which are not very informative in this crystal. We obtained B⁰₂ = 200 cm⁻¹, B⁰₄ = −57 cm⁻¹, B⁰₆ = −40 cm⁻¹, and B⁶₆ = 400 cm⁻¹. The values of B⁰₂ and B⁰₆ differed from the corresponding values for the dilute crystal, i.e., Ho³⁺:Y(OH)₃, as reported from spectral studies. A similar type of difference in the values of CFP for dilute and pure Tb(OH)₃ had also been reported earlier from spectral studies by Scott. The crystal field components of ⁵I₈→⁵I₄ transition in Ho(OH)₃ are matched using our values of CFP. Using the crystal‐field levels as obtained by us, we have shown here that the calculated values for saturated magnetization M_sat, g values, and the Curie constant λ, are quite close to the observed values. From an analysis of each of the components of the total specific heat C_T between 16–0.6 K, we have also shown that the magnetic specific heat has the functional behavior C_M/R = (2.8±0.2)/T², which is nearly the same as in the dilute system. The magnetic entropy S_M was also calculated, and its thermal variation suggested that Ho(OH)₃ behaves as a spin half system around liquid‐helium temperatures but as temperature rises the contributions of the close‐lying excited levels become effective and so Ho(OH)₃ canot be treated as spin half system at such temperatures.