Magnetic and magnetocaloric properties of NdMnO$_{3}$ nanoparticles

Recently nanosized manganites have attracted considerable attention as the reduction of particle size has exotic effect on their properties. We have studied the magnetic properties and magnetocaloric effect (MCE) of NdMnO$_{3 }$nanoparticles with particle size $\sim $20 and 30nm (denoted as S20 and 30 respectively). In temperature dependence of magnetization, M(T), a paramagnetic to ferromagnetic transition is observed at T$_{C}\sim $ 70K for S20, which is 5K higher than that for S30 indicating enhancement of ferromagnetic interaction with particle size reduction. In addition to this, an anomaly in M(T) is observed at 20K (T$_{CA})$ for both S20 and S30, which is attributed to the stabilization of a canted magnetic state (CMS) due to the ordering of Nd$^{3+}$ . The magnetic entropy change [ -$\Delta $S$_{M}$(T)] is calculated from isothermal magnetization curves using Maxwell relation. There are two maximas in -$\Delta $S$_{M}$(T) at T$_{C}$ and T$_{CA}$ indicating large MCE over both temperature regions. Interestingly, the relative cooling power is enhanced in case of smaller particle size in which the influence of stabilization of CMS on MCE is less pronounced.