Large magnetocaloric effect in the Shastry-Sutherland lattice compound <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi mathvariant="normal">Y</mml:mi> <mml:msub> <mml:mi mathvariant="normal">b</mml:mi> <mml:mn>2</mml:mn> </mml:msub> <mml:mi mathvariant="normal">B</mml:mi> <mml:msub> <mml:mi mathvariant="normal">e</mml:mi> <mml:mn>2</mml:mn> </mml:msub> <mml:mi>Ge</mml:mi> <mml:msub> <mml:mi mathvariant="normal">O</mml:mi> <mml:mn>7</mml:mn> </mml:msub> </mml:mrow> </mml:math> with spin-disordered ground state
Andi Liu, Jin Zhou, Lei Wang, Yantao Cao, Fangyuan Song, Yuyan Han, Jingxin Li, Wei Tong, Zhengcai Xia, Zhongwen Ouyang, Jinkui Zhao, Hanjie Guo, Zhaoming Tian
Abstract
Frustrated magnets, especially the ones with spin-disordered ground state, have raised intensive attention as excellent magnetocaloric materials for achieving sub-Kelvin magnetic cooling. Here, we investigate the ultralow-temperature magnetic behaviors and magnetocaloric effect (MCE) down to 60 mK on a frustrated Shastry-Sutherland lattice magnet $\mathrm{Y}{\mathrm{b}}_{2}\mathrm{B}{\mathrm{e}}_{2}\mathrm{Ge}{\mathrm{O}}_{7}$ crystallized into the tetragonal structure with space group $P\overline{4}{2}_{1}m$. The magnetic susceptibility, isothermal magnetization $M$($B$), and specific heat results reveal the Ising-like magnetic anisotropy with easy magnetization along the [001] axis. No sign of long-range magnetic order or spin freezing is detected down to 50 mK, where magnetic susceptibility and specific heat data can be understood by a spin dimer system with small spin gap \ensuremath{\sim}0.78 K. Benefiting from the compatibility of high magnetic ion density (${N}_{\mathrm{mag}}$) \ensuremath{\sim}15.6 $\mathrm{n}{\mathrm{m}}^{\ensuremath{-}3}$ and large Land\'e factor ${g}_{\mathrm{c}}\ensuremath{\sim}4.88$ ($B$ // [001]) with the disordered ground state, $\mathrm{Y}{\mathrm{b}}_{2}\mathrm{B}{\mathrm{e}}_{2}\mathrm{Ge}{\mathrm{O}}_{7}$ exhibits an excellent magnetocaloric response in sub-Kelvin temperature regimes. From the analysis of magnetic entropy $S$($T, B$) landscape, it can be cooled down to the minimum temperatures of ${T}_{\mathrm{min}}\ensuremath{\sim}95$ mK and ${T}_{\mathrm{min}}\ensuremath{\sim}240$ mK from $T$ = 2 K after the adiabatic demagnetization from initial fields of ${B}_{i}=4$ T and ${B}_{i}=2$ T, respectively. The attainable ${T}_{\mathrm{min}}$ and ${N}_{\mathrm{mag}}$ of $\mathrm{Y}{\mathrm{b}}_{2}\mathrm{B}{\mathrm{e}}_{2}\mathrm{Ge}{\mathrm{O}}_{7}$ outperform most of Yb-based quantum magnets and the recently reported spin supersolid candidate $\mathrm{N}{\mathrm{a}}_{2}\mathrm{BaCo}{(\mathrm{P}{\mathrm{O}}_{4})}_{2}$ in the similar working temperature regimes. Therefore, $\mathrm{Y}{\mathrm{b}}_{2}\mathrm{B}{\mathrm{e}}_{2}\mathrm{Ge}{\mathrm{O}}_{7}$ provides a platform for exploring the exotic magnetic states as well as potential application in magnetic refrigeration at sub-Kelvin temperatures.