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

TL;DR

This paper investigates the magnetic properties of a series of lanthanide calcium oxyborates with a quasi-one-dimensional structure, revealing antiferromagnetic interactions and potential magnetocaloric applications at low temperatures.

Contribution

First bulk magnetic characterization of Ca$_4$LnO(BO$_3$)$_3$ compounds, confirming their structure and magnetic behavior, and identifying potential magnetocaloric materials.

Findings

Ca$_4$TbO(BO$_3$)$_3$ shows a magnetic transition at 3.6 K.

All other compounds exhibit antiferromagnetic interactions above 2 K.

Ca$_4$GdO(BO$_3$)$_3$ and Ca$_4$HoO(BO$_3$)$_3$ are promising for low-temperature magnetocaloric applications.

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 $\geq$ 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.