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

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 $T_c=10\mathrm{}$ K and an effective Bohr magneton number $g{\mathrm{}\left[J\right(J+1\mathrm{}\left)\right]}^{\frac{1}{2}}=7.67\mathrm{}$. We can interpret the high-field (up to 125 kOe) magnetization curves for $T<\mathrm{}{T}_c$ using the crystal-field split ${}_{}{}^3{}_{}{}^{}H_6^{}{}_{}{}^{}$ ground state for the ${\mathrm{Tm}}^{3+}$ ion. For the cubic crystal-field parameters we obtain $A_4〈r^4〉=-170\mathrm{}\pm 20$ K, $A_6〈r^6〉=-10\mathrm{}\pm 3$ K. The elastic constant $c_{11}-c_{12}$ 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 $T>\mathrm{}{T}_c$. We interpret the temperature dependence of the $c_{11}-c_{12}$ mode as due to a crystal-field effect, which is particularly pronounced in TmZn because the crystal-field ground state is a doublet ${\Gamma }_3$. The magnetoelastic coupling constant $g_2^2=8.9\mathrm{}$ mK together with an additional quadrupole-quadrupole coupling constant $g^{\prime }=-9.6\mathrm{}$ 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 $T_a=3.16\mathrm{}$ K.