Piezomagnetic Effect of a Rare-earth-based Altermagnet TbPt ₆ Al ₃

We have investigated the piezomagnetic (PZM) effect of the rare-earth-based g-wave altermagnet TbPt6Al3 by magnetization measurements of single-crystalline samples under uniaxial stress sigma. The magnetization in magnetic field along the trigonal a axis increases linearly with sigma for T < TN, indicating the emergence of PZM effect, while the theoretically predicted nonlinear PZM effect was not observed. PZM coefficient of Q11 at 2 K is obtained as 9.1 times 10^-3 mu_B/(f.u. MPa), which is larger by more than two orders of magnitude than those for other altermagnets and noncollinear antiferromagnets. Temperature dependence of Q11 below TN yielded the critical component beta as 0.28, whose value is close to that of the magnetic moment estimated by the neutron powder diffraction. We propose that the large Q11 and the large poling field of 10000 Oe to achieve the single-domain state in TbPt6Al3 are due to the strong relativistic spin-orbit coupling of the 4f electrons in the Tb3+ ions.