Anomalous evolution of the magnetocaloric effect in dilute triangular Ising antiferromagnets Tb\(_{1–x}\)Y\(_x\)(HC O\(_2\))\(_3\)

We investigate the effects of diamagnetic doping in the solid-solution series Tb\(_{1–x}\)Y\(_x\)(HC O\(_2\))\(_3\), in which the parent Tb(HC O\(_2\))\(_3\) phase has previously been shown to host a combination of frustrated and 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 K appears with increasing x. The origin of this unusual behaviour is rationalised in terms of the fragmentation of quasi-1D spin chains by the diamagnetic 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 (HC O\(_2\))\(_3\); however, the magnetocaloric entropy per magnetic Tb\(^{3+}\) ion first decreases then increases with increasing x. Our results establish Tb\(_{1–x}\)Y\(_x\)(HC O\(_2\))\(_3\) as a model system in which to explore the functional ramifications of dilution in a low dimensional magnet.