Large Magnetocaloric Effect in the Kagome Ferromagnet Li9Cr3(P2O7)(3)(PO4)(2)

Single-crystal growth, magnetic properties, and magnetocaloric effect of the S = 3/2 kagome ferromagnet Li9Cr3(P2O7)(3)(PO4)(2) (trigonal, space group: P (3) over bar c1) are reported. Magnetization data suggest dominant ferromagnetic intraplane coupling with a weak anisotropy and the onset of ferromagnetic ordering at TC similar or equal to 2.6 K. Microscopic analysis reveals a very small ratio of interlayer to intralayer ferromagnetic couplings (J(perpendicular to)/J similar or equal to 0.02). Electron spin-resonance data suggest the presence of short-range correlations above TC and confirms the quasi-two-dimensional character of the spin system. A large magnetocaloric effect characterized by isothermal entropy change of -Delta S-m similar or equal to 31 J kg(-1) K-1 and adiabatic temperature change of -Delta T-ad similar or equal to 9 K upon a field sweep of 7 T is observed around T-C. This leads to a large relative cooling power of RCP similar or equal to 284 J kg(-1). The large magnetocaloric effect, together with negligible hysteresis render Li9Cr3(P2O7)(3)(PO4)(2) a promising material for magnetic refrigeration at low temperatures. The magnetocrystalline anisotropy constant K similar or equal to -7.42 x 10(4) erg cm(-3) implies that the compound is an easy-plane-type ferromagnet with the hard axis normal to the ab plane, consistent with the magnetization data.