Tuning the magnetocaloric effect in the Lu-doped frustrated Shastry-Sutherland system TmB4

Abstract

$\mathrm{Tm}{\mathrm{B}}_{4}$ is an anisotropic, metallic magnetic system with geometrical frustration of the Shastry-Sutherland type. Here an experimental study of the magnetocaloric effect (MCE) in Lu-doped $\mathrm{T}{\mathrm{m}}_{1\ensuremath{-}x}\mathrm{L}{\mathrm{u}}_{x}{\mathrm{B}}_{4}$ ($x=0.06$, 0.30), evaluated from the temperature dependence of heat capacity and magnetization curves at 2 K, is presented. The results are described within a theoretical model based on an extended Ising Hamiltonian which considers interactions up to the fourth-next-nearest neighbors. Model parameters were optimized to achieve the best match to the experimental results over the whole range of $\mathrm{L}{\mathrm{u}}^{3+}$ ion concentrations. After optimization a good quantitative agreement with the adiabatic temperature change and a good qualitative agreement with magnetization curves is obtained. Our study shows that the efficiency of the MCE can be tuned by dilution with nonmagnetic Lu ions. The theoretical model developed could be used to design new magnetocaloric materials.