Magnetic properties of monoclinic lanthanide orthoborates, LnBO3, Ln = Gd, Tb, Dy, Ho, Er, Yb

Highlights: • Structural and magnetic properties of lanthanide orthoborates LnBO₃, Ln = Gd, Tb, Dy, Ho, Er, Yb. • LnBO₃ forms a monoclinic structure with the magnetic Ln³⁺ forming eclipsed triangular layers. • With the exception of Gd³⁺ significant single-ion anisotropy is observed for all Ln³⁺. • Ordering features for LnBO₃, Ln = Gd, Tb, Dy, Er between 0.4 and 2 K, onset of magnetic ordering for YbBO₃ at 0.4 K, HoBO₃ forms non-magnetic singlet ground state. • GdBO₃ and DyBO₃ are competitive magnetocaloric materials in the liquid helium temperature regime. - Abstract: The lanthanide orthoborates, LnBO₃, Ln = Gd, Tb, Dy, Ho, Er, Yb crystallise in a monoclinic structure with the magnetic Ln³⁺ 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 ≤ 2 K for Ln = Gd, Tb, Dy, Er. No ordering is observed for YbBO₃ at T ≥ 0.4 K and HoBO₃ is proposed to have a non-magnetic singlet state. Isothermal magnetisation measurements indicate isotropic Gd³⁺ spins and strong single-ion anisotropy for the other Ln³⁺. The change in magnetic entropy has been evaluated to determine the magnetocaloric effect in these materials. GdBO₃ and DyBO₃ are found to be competitive magnetocaloric materials in the liquid helium temperature regime.