Magnetic Properties and Magnetocaloric Effect in Pb-Doped ${rm La}_{0.9}{rm Dy}_{0.1}{rm MnO}_{3}$ Manganites

摘要

We have studied the magnetic properties and magnetocaloric effect of rhombohedral $({rm La}_{0.9}{rm Dy}_{0.1})_{1hbox{-}x}{rm Pb}_{x}{rm MnO}_{3}$ ( $x={0.1}$ , 0.2, and 0.3) fabricated by solid-state reaction. Thermomagnetization curve reveals that the increase of Pb doping in $({rm La}_{0.9}{rm Dy}_{0.1})_{1hbox{-}x}{rm Pb}_{x}{rm MnO}_{3}$ shifts the ferromagnetic (FM)–paramagnetic (PM) phase-transition temperature $(T_{C})$ toward room temperature; the $T_{C}$ values determined for $x={0.1}$ , 0.2, and 0.3 are about 172, 249, and 322 K, respectively. Based on magnetic-field dependencies of magnetization, $M(H)$ , the magnetic entropy changes $(Delta S_{m})$ of the samples were calculated. Under an applied magnetic field of $H={10}~{rm kOe}$ , the $vertDelta S_{rm max}vert$ value slightly increases from 0.74 ${rm J}/{rm kg}cdot~{rm K}$ for $x={rm 0.1}$ to about 1.1 ${rm J}/{rm kg}cdot~{rm K}$ for $x={rm 0.2}$ and 0.3. These results correspond to a relative c- oling power of ${sim}{rm 50}~{rm J}/{rm kg}$ , which is comparable with some perovskite manganites, indicating the applicability of $({rm La}_{0.9}{rm Dy}_{0.1})_{1hbox{-}x}{rm Pb}_{x}{rm MnO}_{3}$ in magnetic refrigeration devices working around room temperature. Particularly, we find that the variation of $vertDelta S_{rm max}vert$ versus the magnetic field $H$ can be described by a power law $vertDelta S_{rm max}vertpropto H^{n}$ , where the magnetic-ordering parameter $(n)$ decreases from 0.861 for $x={0.1}{-}0.834$ for $x={rm 0.3}$ . A deviation of the $n$ values estimated from the mean-field theory $(n=2/3)$ demonstrates an existence of short-range FM order in the samples.