Magnetic properties of monoclinic lanthanide orthoborates, $Ln$BO$_3$, $Ln$ = Gd, Tb, Dy, Ho, Er, Yb

TL;DR

This study investigates the magnetic properties of monoclinic lanthanide orthoborates, revealing their magnetic ordering behaviors, anisotropies, and potential as magnetocaloric materials at low temperatures.

Contribution

It provides detailed magnetic characterization of $Ln$BO$_3$ compounds, highlighting their ordering temperatures, anisotropy, and magnetocaloric potential, which was not previously reported.

Findings

Gd, Tb, Dy, Er orthoborates show magnetic ordering below 2 K.

YbBO$_3$ remains disordered down to 0.4 K.

GdBO$_3$ and DyBO$_3$ exhibit promising magnetocaloric effects.

Abstract

The lanthanide orthoborates, $Ln$BO$_3$, $Ln$ = Gd, Tb, Dy, Ho, Er, Yb crystallise in a monoclinic structure with the magnetic $Ln^{3+}$ forming an edge-sharing triangular lattice. The triangles are scalene, however all deviations from the ideal equilateral geometry are less than 1.5%. The bulk magnetic properties are studied using magnetic susceptibility, specific heat and isothermal magnetisation measurements. Heat capacity measurements show ordering features at $T \leq$ 2 K for $Ln$ = Gd, Tb, Dy, Er. No ordering is observed for YbBO$_3$ at $T \geq$ 0.4 K and HoBO$_3$ is proposed to have a non-magnetic singlet state. Isothermal magnetisation measurements indicate isotropic Gd$^{3+}$ spins and strong single-ion anisotropy for the other $Ln^{3+}$. The change in magnetic entropy has been evaluated to determine the magnetocaloric effect in these materials. GdBO$_3$ and DyBO$_3$ are found to be competitive magnetocaloric materials in the liquid helium temperature regime.