Abstract We report changes on the magnetic behavior of the Heavy-Fermion ferromagnetic YbNi 2 alloy when reducing the size of the particles to the nanometer scale by high-energy ball milling. The milling process induces a reduction on the particle size of the bulk alloy down to 10 (2) nm and a lattice strain of 1.8 (2)%, for 30 h of milling time, as calculated from the X-ray diffraction data. The ferromagnetic transition at T C = 10.5 K in the bulk alloy tends to disappear whereas other magnetic transitions arise at lower temperatures with the milling process. The AC magnetic susceptibility of the 30 h milled sample shows a frequency independent peak at 3 K, in a wide range of frequencies, consistent neither with superparamagnetic nor simple freezing of the magnetic moments, and as expected for a ferromagnetic behavior. However, from the specific heat measurements in the 30 h milled sample, a peak at 3.6 K is shifted respect to that observed in the AC magnetic susceptibility, as found in spin glasses. Additionally, the specific heat on nanometric samples show reduced magnetic contributions respect to the bulk alloy with Δ c max around 0.45 J/molK. The results are explained by the influence of magnetic inhomogeneities and disorder of the alloys enhanced by the milling process in the ensemble of nanoparticles.

中文翻译：

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YbNi2纳米颗粒中铁磁性和自旋玻璃态的共存

摘要 我们报告了当通过高能球磨将颗粒尺寸减小到纳米级时，重费米子铁磁 YbNi 2 合金的磁行为发生了变化。根据 X 射线衍射数据计算，在 30 小时的研磨时间内，研磨过程将大块合金的粒径减小至 10 (2) nm，晶格应变为 1.8 (2)%。大块合金中 TC = 10.5 K 时的铁磁转变趋于消失，而其他磁转变在较低温度下随着铣削过程出现。30 小时研磨样品的 AC 磁化率在 3 K 处显示一个频率独立的峰值，在很宽的频率范围内，既不符合超顺磁性，也不符合磁矩的简单冻结，并且符合铁磁行为的预期。然而，从 30 小时研磨样品的比热测量结果来看，3.6 K 处的峰值相对于在自旋玻璃中发现的 AC 磁化率中观察到的峰值发生了偏移。此外，纳米样品的比热显示出对大块合金的磁性贡献降低，Δ c max 约为 0.45 J/molK。结果可以通过纳米粒子集合中的研磨过程增强的合金磁不均匀性和无序的影响来解释。