Magnetocaloric properties of Eu_1-_xLa_xTiO_3 (0.01 ≤ x ≤ 0.2) for cryogenic magnetic cooling

摘要

We report magnetic and magnetocaloric (MCE) properties of polycrystalline Eu_(1-x)La_xTiO_3 samples over a wide composition range (0.01 ≤ x ≤ 0.20). It is found that the ground state changes from antiferromagnetic for x = 0.01 (T_N = 5.2K) to ferromagnetic for x≥0.03 and the ferromagnetic Curie temperature increases from T_C = 5.7 K for x = 0.03 to T_C = 7.9 K for x = 0.20. The x = 0.01 sample shows a large reversible isothermal magnetic entropy change of - ΔS_m = 23 (41.5) J/kg K and adiabatic temperature change of ΔT_(ad) = 9 (17.2) K around 6.7 K for a field change of μ_0ΔH = 2 (5) Tesla. Although the peak value of -ΔS_m decreases as La content increases, it is impressive in x = 0.2(-ΔS_m = 31.41 J/kgK at T=7.5K for μ_0ΔH = 5T). The large value of MCE arises from suppression of the spin entropy associated with the localized moment (J = 7/2) of Eu~(2+):4f~7 ions. This large MCE over a wide compositional range suggests that the Eu_(1-x)La_xTiO_3 series could be useful for magnetic cooling below 40 K.