Dy取代YMn$_2$O$_5$化合物磁卡行为的研究
A study of the magnetocaloric behavior of Dy-substituted YMn$_2$O$_5$ compounds
AI总结：
本文研究了Dy取代YMn2O5的磁性和磁卡特性，发现其在13 K附近具有大磁卡效应，且制冷容量高于单晶样品，是低温氢氦液化等领域的理想磁制冷剂候选材料。
摘要：
本文报告了通过溶胶-凝胶法制备的Dy取代YMn$_2$O$_5$（Y$_{1-x}$Dy$_x$Mn$_2$O$_5$，x=0.6、0.8和1）系列的磁性和磁卡特性。X射线衍射和拉曼测量充分证明了多晶样品的高质量，其结晶为具有Pbam空间群的正交结构。在室温下对拉曼声子频率进行了测量，并与晶格动力学计算结果进行比较，以确定所有检测到的振动模式的振动特性。正如预期，磁化研究表明，用Dy$^{3+}$取代Y$^{3+}$增强了磁化强度。Dy取代的YMn$_2$O$_5$的Néel转变[TN (Mn)]位于40至45 K温度范围内，有利于在极低温度下出现由Dy$^{3+}$磁矩在13 K以下长程有序引起的转变[TN (Dy)]。在磁熵变曲线中也观察到了双峰，与磁化数据吻合良好，这扩大了这些材料的应用范围。另一方面，在13 K附近观察到的大磁卡效应主要归因于Dy$^{3+}$磁矩的有序化。此外，约40 K处发生的Mn磁矩非公度反铁磁转变也轻微影响了熵变。我们的制冷容量（RC）结果高于HoMn$_2$O$_5$和TbMn$_2$O$_5$单晶样品a、b、c轴RC的平均值，这证实我们的多晶材料是有前景的磁制冷剂候选者，可应用于空间技术及低温下的氢和氦液化。
英文摘要：
In this paper, we report on the magnetic and magnetocaloric features of Dy-substituted YMn$_2$O$_5$ (Y$_{1-x}$Dy$_x$Mn$_2$O$_5$) with $x=$ 0.6, 0.8, and 1 series elaborated by sol-gel method. X-ray diffraction and Raman measurements attest well the high quality of our polycrystalline samples that crystallize in an orthorhombic structure with the Pbam space group. The Raman phonon frequencies were carried out and compared with the lattice dynamics calculations to identify the vibrational properties of all detected modes at room temperature. As expected, our magnetic study reveals that the magnetization was enhanced by the substitution of Y$^{3+}$ by Dy$^{3+}$. The Dy-substituted YMn$_2$O$_5$ sets the Néel transition [TN (Mn)] in the temperature range going from 40 to 45 K favoring the emergence of a transition at a very low temperature due to the long-range ordering of the Dy3+ magnetic moments below 13K [TN (Dy)]. Dual peaks in the magnetic entropy change curve are also observed being in good agreement with magnetization data, which enlarges the range of application of these materials. On the other hand, a large magnetocaloric effect is observed close to 13 K which is mainly due the ordering of Dy$^{3+}$ magnetic moments. Also, the incommensurate antiferromagnetic transition of Mn magnetic moment taking place around 40 K affects slightly the entropy change. Our refrigerant capacity (RC) findings are higher compared to the average of RC for a, b, c axis of single crystal samples as HoMn$_2$O$_5$ and TbMn$_2$O$_5$, which confirms that our polycrystalline materials stand for promising magnetic refrigerant candidates that can be invested in space technology, hydrogen and helium liquefaction at cryogenic temperature.
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