Anomalous evolution of the magnetocaloric effect in dilute triangular Ising antiferromagnets Tb1−xYx(HCO2

We investigate the effects of diamagnetic doping in the solid-solution series ${\mathrm{Tb}}_{1\text{\ensuremath{-}}x}{\mathrm{Y}}_{x}{(\mathrm{HC}{\mathrm{O}}_{2})}_{3}$, in which the parent $\mathrm{Tb}{({\mathrm{HCO}}_{2})}_{3}$ phase has previously been shown to host a combination of frustrated and quasi-one-dimensional (quasi-1D) physics, giving rise to a triangular Ising antiferromagnetic ground state that lacks long range 3D order. Heat capacity measurements show three key features: (i) a low temperature Schottky anomaly is observed, which is constant as a function of $x$; (ii) the transition temperature and associated entropy change are both surprisingly robust to diamagnetic doping; and (iii) an additional contribution at $T<0.4\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ appears with increasing $x$. The origin of this unusual behavior is rationalized in terms of the fragmentation of quasi-1D spin chains by the diamagnetic ${\mathrm{Y}}^{3+}$ dopant. Magnetocaloric measurements show a nonlinear dependence on $x$. The mass-weighted magnetocaloric entropy decreases across the series from the promising values in $\mathrm{Tb}{({\mathrm{HCO}}_{2})}_{3}$; however, the magnetocaloric entropy per magnetic ${\mathrm{Tb}}^{3+}$ ion first decreases then increases with increasing $x$. Our results establish ${\mathrm{Tb}}_{1\text{\ensuremath{-}}x}{\mathrm{Y}}_{x}{(\mathrm{HC}{\mathrm{O}}_{2})}_{3}$ as a model system in which to explore the functional ramifications of dilution in a low-dimensional magnet.