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 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.
KeywordsCo-Ni-Ga nanoparticles chemical synthesis size magnetic properties
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We acknowledge financial supports by the German Research Foundation (DFG) under the Project of TP 2.3-A in research unit FOR 1464 “ASPIMATT” and the ERC Advanced Grant (291472 Idea Heusler). The authors are also grateful to Prof. A. Hütten (Department of Physics, Bielefeld University) for stimulating discussions; Dr. R. Ramlau and Ms. U. Köhler (MPICPfS) for TEM support; Dr. G. Auffermann (MPI-CPfS) for the chemical analysis; Dr. H. Borrmann (MPICPfS) for support of the HTXRD measurements; Prof. S. Kaskel (Department of Inorganic Chemistry, Technical University of Dresden) for the nitrogen adsorption measurements; Mr. R. Koban for kind help with sample preparation and magnetic measurements; Dr. L. Olivi (Elettra Sincrotrone Trieste) for stimulating discussion and kind help with the XANES experiments. The XANES measurements were performed at the Elettra Sincrotrone Trieste (Trieste, Italy) under the approval of proposal No. 20140471 and at the “National Synchrotron Radiation Research Center” (NSRRC, Hsinchu, Taiwan, China) under the approval of proposal No. 2013-2-027-4.
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