Phase transitions and magnetic properties of shape-memory materials can be tailored by tuning the size of the constituent materials, such as nanoparticles. However, owing to the lack of suitable synthetic methods for size-controlled Heusler nanoparticles, there is no report on the size dependence of their properties and functionalities. In this contribution, we present the first chemical synthesis of size-selected Co-Ni-Ga Heusler nanoparticles. We also report the structure and magnetic properties of the biphasic Co-Ni-Ga nanoparticles with sizes in the range of 30–84 nm, prepared by a SBA-15 nanoporous silicatemplated approach. The particle sizes could be readily tuned by controlling the loading and concentration of the precursors. The fractions and crystallite sizes of each phase of the Co-Ni-Ga nanoparticles are closely related to their particle size. Enhanced magnetization and decreased coercivity are observed with increasing particle size. The Curie temperature (T_c) of the Co-Ni-Ga nanoparticles also depends on their size. The 84 nm-sized particles exhibit the highest T_c (≈ 1,174 K) among all known Heusler compounds. The very high Curie temperatures of the Co-Ni-Ga nanoparticles render them promising candidates for application in high-temperature shape memory alloy-based devices.

中文翻译：

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化学合成的Co-Ni-Ga纳米粒子的尺寸依赖性结构和磁性

形状记忆材料的相变和磁性可以通过调整组成材料（例如纳米粒子）的尺寸来调整。但是，由于缺乏适用于尺寸控制的Heusler纳米粒子的合适合成方法，因此没有关于其性质和功能的尺寸依赖性的报道。在这项贡献中，我们提出了尺寸选择的Co-Ni-Ga Heusler纳米粒子的第一个化学合成方法。我们还报告了通过SBA-15纳米多孔二氧化硅模板化方法制备的尺寸为30-84 nm的双相Co-Ni-Ga纳米颗粒的结构和磁性。通过控制前体的负载和浓度可以容易地调节粒度。Co-Ni-Ga纳米粒子的每个相的分数和微晶尺寸与其粒径密切相关。随着粒度增加，观察到增强的磁化强度和降低的矫顽力。居里温度Co-Ni-Ga纳米颗粒的T _c）也取决于它们的尺寸。在所有已知的Heusler化合物中，84 nm大小的颗粒显示出最高的T _c（≈1,174 K）。Co-Ni-Ga纳米粒子的居里温度很高，使其有希望在高温形状记忆合金基器件中应用。