Magnetic properties of quasi-one-dimensional lanthanide calcium oxyborates Ca${}_4$LnO(BO${}_3$)${}_3$

Abstract

This study examines the lanthanide calcium oxyborates Ca${}_4$LnO(BO${}_3$)${}_3$ (Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y, Er, Yb). The reported monoclinic structure (space group $Cm$) was confirmed using powder X-ray diffraction. The magnetic Ln${}^{3+}$ ions are situated in well-separated chains parallel to the c axis in a quasi-one-dimensional array. Here we report the first bulk magnetic characterisation of Ca${}_4$LnO(BO${}_3$)${}_3$ using magnetic susceptibility $\chi$(T) and isothermal magnetisation M(H) measurements at T $\ge$ 2 K. With the sole exception of Ca${}_4$TbO(BO${}_3$)${}_3$, which displays a transition at T = 3.6 K, no magnetic transitions occur above 2 K, and Curie-Weiss analysis indicates antiferromagnetic nearest-neighbour interactions for all samples. Calculation of the magnetic entropy change $\Delta S_m$ indicates that Ca${}_4$GdO(BO${}_3$)${}_3$ and Ca${}_4$HoO(BO${}_3$)${}_3$ are viable magnetocaloric materials at liquid helium temperatures in the high-field and low-field regimes respectively.

9 pages, 6 figures. Accepted by Inorganic Chemistry, 28 May 2020

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