Large Magnetocaloric Effect in the Kagome Ferromagnet <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><mml:msub><mml:mi>Li</mml:mi><mml:mn>9</mml:mn></mml:msub><mml:msub><mml:mi>Cr</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:mo stretchy="false">(</mml:mo><mml:msub><mml:mi mathvariant="normal">P</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>7</mml:mn></mml:msub><mml:msub><mml:mo stretchy="false">)</mml:mo><mml:mn>3</mml:mn></mml:msub><mml:mo stretchy="false">(</mml:mo><mml:msub><mml:mi>PO</mml:mi><mml:mn>4</mml:mn></mml:msub><mml:msub><mml:mo stretchy="false">)</mml:mo><mml:mn>2</mml:mn></mml:msub></mml:math>

Abstract

Single-crystal growth, magnetic properties, and magnetocaloric effect of the $S=3/2$ kagome ferromagnet ${\mathrm{Li}}_{9}{\mathrm{Cr}}_{3}({\mathrm{P}}_{2}{\mathrm{O}}_{7}{)}_{3}({\mathrm{PO}}_{4}{)}_{2}$ (trigonal, space group: $P\overline{3}c1$) are reported. Magnetization data suggest dominant ferromagnetic intraplane coupling with a weak anisotropy and the onset of ferromagnetic ordering at ${T}_{C}\ensuremath{\simeq}2.6$ K. Microscopic analysis reveals a very small ratio of interlayer to intralayer ferromagnetic couplings (${J}_{\ensuremath{\perp}}/J\ensuremath{\simeq}0.02$). Electron spin-resonance data suggest the presence of short-range correlations above ${T}_{C}$ and confirms the quasi-two-dimensional character of the spin system. A large magnetocaloric effect characterized by isothermal entropy change of $\ensuremath{-}\mathrm{\ensuremath{\Delta}}{S}_{m}\ensuremath{\simeq}31\phantom{\rule{0.2em}{0ex}}\mathrm{J}\phantom{\rule{0.2em}{0ex}}{\mathrm{kg}}^{\ensuremath{-}1}\phantom{\rule{0.2em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ and adiabatic temperature change of $\ensuremath{-}\mathrm{\ensuremath{\Delta}}{T}_{\mathrm{ad}}\ensuremath{\simeq}9\phantom{\rule{0.2em}{0ex}}\mathrm{K}$ upon a field sweep of 7 T is observed around ${T}_{C}$. This leads to a large relative cooling power of $\mathrm{RCP}\ensuremath{\simeq}284\phantom{\rule{0.2em}{0ex}}\mathrm{J}\phantom{\rule{0.2em}{0ex}}{\mathrm{kg}}^{\ensuremath{-}1}$. The large magnetocaloric effect, together with negligible hysteresis render ${\mathrm{Li}}_{9}{\mathrm{Cr}}_{3}({\mathrm{P}}_{2}{\mathrm{O}}_{7}{)}_{3}({\mathrm{PO}}_{4}{)}_{2}$ a promising material for magnetic refrigeration at low temperatures. The magnetocrystalline anisotropy constant $K\ensuremath{\simeq}\ensuremath{-}7.42\ifmmode\times\else\texttimes\fi{}{10}^{4}\phantom{\rule{0.2em}{0ex}}\mathrm{erg}\phantom{\rule{0.2em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$ implies that the compound is an easy-plane-type ferromagnet with the hard axis normal to the $a$$b$ plane, consistent with the magnetization data.

Topics & Concepts