碳屏蔽NiPt纳米合金的可调磁性能
Tunable Magnetic Properties of Carbon-shielded NiPt Nanoalloys
摘要：
采用高压化学气相沉积法制备了包裹在碳壳中的球形NiPt@C纳米合金。通过改变合成参数，可以控制球形NixPt（1-x@C）纳米胶囊的合金芯成分和颗粒尺寸。发现Ni和Pt前体的升华温度是控制合金组成和直径的关键。根据合成参数，核的直径在3 - 15 nm范围内可调，而所有条件下的碳涂层为1 - 2 nm。核心颗粒尺寸线性减小时的升华温度的增加，而Ni和Pt的含量，分别与相关的前体温度线性增加。因此，纳米合金的磁性，即磁化强度、回复磁化强度和临界场，很好地由两个升华温度控制。与大块NiPt相比，我们的数据显示，由于铁磁性出现在富含Pt的NiPt纳米合金中，因此通过纳米尺度增加了Stoner增强，这对于相关的大块合金是没有观察到的。磁晶各向异性常数K在0.3 - 4 × 105 J/m3的范围内，这表明NiPtC是一种稳定的高磁性功能纳米材料。
英文摘要：
Spherical NiPt@C nanoalloys encapsulated in carbon shells are synthesized by means of high-pressure chemical vapour deposition. Upon variation of the synthesis parameters, both the alloy core composition and the particle size of the resulting spherical NixPt1-x@C nanocapsules can be controlled. The sublimation temperatures of the Ni- and Pt-precursors are found key to control the alloy composition and diameter. Depending on the synthesis parameters, the diameters of the cores are tuneable in the range of 3 - 15 nm while the carbon coatings for all conditions are 1 - 2 nm. The core particle size decreases linearly upon increasing either of the sublimation temperatures while the Ni and Pt content, respectively, are linearly increasing with the related precursor temperature. Accordingly, the magnetic properties of the nanoalloys, i.e. magnetization, remanent magnetization and critical field, are well controlled by the two sublimation temperatures. As compared to bulk NiPt, our data show an increase of Stoner enhancement by nanoscaling as ferromagnetism appears in the Pt rich NiPt nanoalloy which is not observed for the related bulk alloys. The magneto-crystalline anisotropy constants K are in the range of 0.3 - 4 x 105 J/m3 underlining that NiPt@C is a stable, highly magnetic functional nanomaterial.
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