Crystal electric field and magnetic-ion-lattice interactions in TmZn

Abstract

Experimental results on magnetic and elastic properties for the cubic intermetallic compound TmZn are presented. The magnetic-susceptibility measurement gives a ferromagnetic ordering temperature of ${T}_{c}=10$ K and an effective Bohr magneton number $g{[J(J+1)]}^{\frac{1}{2}}=7.67$. We can interpret the high-field (up to 125 kOe) magnetization curves for $Tl{T}_{c}$ using the crystal-field split $^{3}H_{6}$ ground state for the ${\mathrm{Tm}}^{3+}$ ion. For the cubic crystal-field parameters we obtain ${A}_{4}〈{r}^{4}〉=\ensuremath{-}170\ifmmode\pm\else\textpm\fi{}20$ K, ${A}_{6}〈{r}^{6}〉=\ensuremath{-}10\ifmmode\pm\else\textpm\fi{}3$ K. The elastic constant ${c}_{11}\ensuremath{-}{c}_{12}$ shows a softening of 40% from room temperature down to 13 K. The ${c}_{44}$ mode and the bulk modulus show a normal temperature dependence for $Tg{T}_{c}$. We interpret the temperature dependence of the ${c}_{11}\ensuremath{-}{c}_{12}$ mode as due to a crystal-field effect, which is particularly pronounced in TmZn because the crystal-field ground state is a doublet ${\ensuremath{\Gamma}}_{3}$. The magnetoelastic coupling constant ${g}_{2}^{2}=8.9$ mK together with an additional quadrupole-quadrupole coupling constant ${g}^{\ensuremath{'}}=\ensuremath{-}9.6$ mK are not strong enough to induce a structural transition in the absence of exchange interactions. We compare these results to the recently investigated TmCd compound, which exhibits no magnetic transition but a structural transition at ${T}_{a}=3.16$ K.