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

Falsaperna, Mario, Bulled, Johnathan M., Stenning, Gavin B. G., Goodwin, Andrew L., Saines, P.J. (2022) Anomalous evolution of the magnetocaloric effect in dilute triangular Ising antiferromagnets Tb$$_{1–x}$$Y$$_x$$(HC O$$_2$$)$$_3$$. Physical Review Materials, 6 (12). Article Number 124410. ISSN 2475-9953. (doi:10.1103/PhysRevMaterials.6.124410) (KAR id:98725)

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.