Preparation and characterization of SiO2-coated submicron-sized face-centered tetragonal L10 Fe-Pt particles (Research Paper Sample)

Preparation and characterization of SiO2-coated submicron-sized face-centered tetragonal L10 Fe-Pt particles
Abstract
The fabrication of the optimal microstructure is essential for enhancing the coercivity of the permanent magnets. In this workstudy, in order to obtainwe aim to synthesize particles for fabricating the magnets with the an ideal microstructure,. wWe attempted to fabricate face-centered tetragonal structured L10 Fe-Pt/SiO2-core/shell particles with submicron-sized cores less smaller than the critical size for a single domain and investigated their characterscharacteristics. Through the morphology morphological observation and observation and XRD analysis of the particles, confirmed that the fabrication of the L10 Fe-Pt/SiO2-core/shell particles were fabricated with submicron-sized cores, less smaller than the critical size for a single domain. were confirmed. Though the The fabrication of the ideal core/shell particles was not achieved because the L10 Fe-Pt cares cores were polycrystalline,. the However, L10 Fe-Pt/SiO2-core/shell particles with a high coercivity of 25 kOe were obtained.
Keywords: optimal microstructure, face-centered tetragonal structure, core/shell nanoparticle, Fe-Pt/SiO2-core/shell, high coercivity, submicron-size cores, permanent magnet.
* INTRODUCTIONIntroduction
Permanent magnets are widely used in various applications such as generators and motors, and the, and the development of higher performance magnets is is gaining increasing desirableinterest. One approach to enhance the properties of the magnet is to The optimizoptimizeation of their its structure. is an approach for enhancing their properties, and a A microstructure comprising magnetically isolated hard magnetic grains of a single domain size is suggested as an ideal structure to enhance their coercivity 1. However, it is very difficultchallenging to realize achieve the ideal structure, because the fabrication of the ideal structure requires to better controlling the properties such as the grain size, grain shape, non-magnetic grain boundary phase, and so onmore. To overcome this difficultOne structure control, we consider an avenue is to use approach based on core/shell nanoparticles, with having a hard magnetic core and non-magnetic shell. This approach can be expectedserve to obtain magnets with a structure consisting of the magnetically isolated hard magnetic nanoparticles, magnetically isolated by the non-magnetic shells. Taccording to the nanoparticles’ core/shell structure of the nanoparticles appears to and tohave better control over the structure of a the obtained magnets through control over the core size and shell thickness. of the core/shell nanoparticles.
As theThe hard magnetichard-magnetic core material , are face- centered tetragonal (L10) Fe-Pt nanoparticles that are considered to be useful for the magnets, based on core/shell nanoparticles because of their high magnet to crystalline anisotropy2and good chemical stability. Furthermore, various studies it is knownstate that the core/shell nanoparticles3 and granular films4 with structure consisting of magnetically isolated L10 Fe-Pt nanoparticles show very high coercivity. On the other hand, many of thePreliminary studies also report that reported Fe-Pt nanoparticles synthesized by chemical methods have the sizes dimensions less smaller than several tens of nanometers5-6. Using Since the core/shell nanoparticles whose have a magnetic core size is less than several tens of nanometers, the magnetization value of the fabricated magnets is presumed to largely decrease, due to thebecause relatively the large volume fraction of the non-magnetic shells increases. For example, in the case of a spherical core/shell nanoparticle with the a magnetic core size of 10 nm and the a non-magnetic shell thickness of 1 nm, the volume fraction of non-magnetic shell is approximately 42 vol.%. Therefore, because as the critical size for a single domain of hard magnetic particles is is of submicron-size2, core/shell particles with submicron-size hard magnetic cores seem to be suitable as the raw materials for the magnets based on core/shell particles. In in the case of face-centered tetragonal (L10) Fe-Pt particles, the critical size is approximately 340 nm2.
In this paperstudy, with an aim to obtain particles for our proposed approach, wewe used our proposed approach as an attempt attempted to fabricate face-centered tetragonal structured (L10) Fe-Pt/SiO2-core/shell particles with submicron-sized cores less than the critical size for a single domain and investigated their characterscharacteristics.