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Large magnetocaloric entropy change at room temperature in soft ferromagnetic manganites

机译：软铁磁锰矿中室温的大磁热熵变化

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In this paper, La _(0.75) Ca _(0.25? x ) Na _( x ) MnO _(3) ( x = 0.15 and 0.20) samples were prepared by the flux method. Crystallographic study revealed that the x = 0.15 sample is characterized by the coexistence of a mixture of orthorhombic and rhombohedral structures with Pbnm and R c space groups, respectively. While, the x = 0.20 sample crystallized in the rhombohedral structure with a R c space group. Magnetic data, under a magnetic field of 0.05 T, indicated that our samples undergo a ferromagnetic (FM)–paramagnetic (PM) phase transition, on increasing the temperature. The magnetic field dependence of the magnetocaloric properties of La _(0.75) Ca _(0.25? x ) Na _( x ) MnO _(3) ( x = 0.15 and 0.20) samples, with the second phase transition, was investigated. Near room temperature, the x = 0.20 sample exhibited a large magnetic entropy change with maxima of 6.01 and 3.12 J kg ~(?1) K ~(?1) , respectively, under applied magnetic fields of 5 and 2 T. Also, the relative cooling power (RCP) was calculated. According to hysteresis cycles, for our studied samples, at 10 K a typical soft FM behavior with a low coercive field was observed. These results make our samples promising candidates for magnetic refrigerators, magnetic recording, and memory devices.
机译：在本文中，通量法制备了La _（0.75）Ca _（0.25？x）Na _（x）MnO _（3）（x = 0.15和0.20）样品。晶体学研究表明，x = 0.15样品的特征是正交晶和菱面体结构分别与Pbnm和R c空间基团共存。同时，x = 0.20样品在具有R c空间基团的菱面体结构中结晶。在0.05 T磁场下的磁数据表明，随着温度的升高，我们的样品经历了铁磁（FM）-顺磁（PM）相变。研究了La _（0.75）Ca _（0.25？x）Na _（x）MnO _（3）（x = 0.15和0.20）样品的磁热特性与第二相变的磁场依赖性。在室温附近，x = 0.20样品在5和2 T的施加磁场下表现出较大的磁熵变，最大值分别为6.01和3.12 J kg〜（？1）K〜（？1）。计算了相对冷却功率（RCP）。根据滞后循环，对于我们研究的样品，在10 K时观察到典型的软FM行为，且矫顽场低。这些结果使我们的样品有望用于磁性冰箱，磁性记录和存储设备。

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