Magnetic properties of the quasi-1D magnesium lanthanide borates MgLnB5O₁₀

Lanthanide borates are widely studied for their optical and magnetic properties. A wide variety of structures are known with 3, 2, 1 and 0 dimensional connectivity of lanthanide ions. Here, we explore MgLnB5O₁₀, with a quasi-1D arrangement of theLnions. Polycrystalline samples of MgLnB5O₁₀(Ln= La, Pr, Nd, Sm-Er) were synthesised via a solution-based method, which achieved higher purity than a solid-state method. Powder x-ray diffraction data confirmed the reported monoclinic space group (P21/c). The magneticLn3+ions in MgLnB5O₁₀form relatively isolated zig-zag chains parallel to thebaxis. Magnetic susceptibility and isothermal magnetisation were measured: all samples exceptLn=(Eu, Sm) fit the Curie-Weiss Law in isothermal magnetisation at high temperatures, in broad agreement with theoretical expectations.Ln=(Nd, Tb, Dy, Ho, Er) exhibit signatures characteristic of Ising spin saturation, implying single ion anisotropy, while Gd exhibits characteristics of Heisenberg spins. Estimation of magnetic interactions suggests that MgLnB5O₁₀are candidate materials for quasi-1D magnetism. The magnetocaloric entropy change was also calculated, with MgGdB₅O₁₀showing promise for application to solid-state refrigeration at liquid helium temperatures.