Size-dependent structural and magnetic properties of chemically synthesized Co-Ni-Ga nanoparticles

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 partide size.The Curie temperature (Tc) of the Co-Ni-Ga nanoparticles also depends on their size.The 84 nm-sized particles exhibit the highest Tc (≈ 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.