Abstract Magnetocaloric properties of the intermetallic DyCo2 compound (in the form of reduced size particles) and its correlations with the itinerant electron metamagnetism (IEM) phenomenon and structural disorders are investigated and discussed. Micrometric-sized particles were prepared by a mechanical milling technique for two low milling times (4 and 8 h) and characterized by means of X-ray diffraction, scanning and high-resolution transmission electron microscopy as well as magnetic measurements as a function of an applied external magnetic field and temperature. The results show that the particles have irregular-shaped and amorphous “edges/ledges” with embedded randomly oriented DyCo2 nanocrystallites. The average particle size practically does not change with increasing milling time, whereas the average crystallite size is slightly diminished. In contrast, microstrain values that indicate lattice deformation degree were rather increased after the milling processes. Structural disorders and surface effects, features resulting from mechanical impact, disturb the Dy-Co sublattice coupling and weaken the IEM mechanism responsible for the high magnetocaloric effect found for the DyCo2 bulk sample. For the milled samples, it was observed reductions in the peak intensity of the magnetic entropy change (−ΔSM) and substantial broadenings of the distribution profiles which have contributed to an increase of the working temperature range of the investigated magnetocaloric material.

中文翻译：

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结构无序对 DyCo 2 金属间化合物磁熵变的影响：机械研磨和流动电子变磁机制的减弱

摘要 研究和讨论了金属间 DyCo2 化合物（以减小尺寸的颗粒形式）的磁热特性及其与巡回电子变磁 (IEM) 现象和结构紊乱的相关性。通过机械研磨技术制备了两个低研磨时间（4 小时和 8 小时）的微米级颗粒，并通过 X 射线衍射、扫描和高分辨率透射电子显微镜以及磁性测量进行表征。施加外部磁场和温度。结果表明，这些颗粒具有不规则形状和无定形的“边缘/壁架”，其中嵌入了随机取向的 DyCo2 纳米微晶。平均粒径实际上不会随着研磨时间的增加而改变，而平均微晶尺寸略有减小。相比之下，表明晶格变形程度的微应变值在铣削过程后反而增加了。结构紊乱和表面效应，机械冲击产生的特征，会干扰 Dy-Co 亚晶格耦合并削弱 IEM 机制，导致 DyCo2 块状样品的高磁热效应。对于研磨样品，观察到磁熵变 (-ΔSM) 的峰值强度降低，分布曲线显着加宽，这有助于增加所研究的磁热材料的工作温度范围。结构紊乱和表面效应，机械冲击产生的特征，会干扰 Dy-Co 亚晶格耦合并削弱 IEM 机制，导致 DyCo2 大块样品的高磁热效应。对于研磨样品，观察到磁熵变 (-ΔSM) 的峰值强度降低，分布曲线显着加宽，这有助于增加所研究的磁热材料的工作温度范围。结构紊乱和表面效应，机械冲击产生的特征，会干扰 Dy-Co 亚晶格耦合并削弱 IEM 机制，导致 DyCo2 大块样品的高磁热效应。对于研磨样品，观察到磁熵变 (-ΔSM) 的峰值强度降低，分布曲线显着加宽，这有助于增加所研究的磁热材料的工作温度范围。