Abstract
This paper presents domain and structure studies of bonded magnets made from nanocrystalline Nd-(Fe, Co)-B powder. The structure studies were investigated using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Mössbauer spectroscopy and X-ray diffractometry. On the basis of performed qualitative and quantitative phase composition studies, it was found that investigated alloy was mainly composed of Nd2(Fe-Co)14B hard magnetic phase (98 vol%) and a small amount of Nd1.1Fe4B4 paramagnetic phase (2 vol%). The best fit of grain size distribution was achieved for the lognormal function. The mean grain size determined from transmission electron microscopy (TEM) images on the basis of grain size distribution and diffraction pattern using the Bragg equation was about ≈130 nm. HRTEM images showed that over-stoichiometric Nd was mainly distributed on the grain boundaries as a thin amorphous border of 2 nm in width. The domain structure was investigated using a scanning electron microscope and metallographic light microscope, respectively, by Bitter and Kerr methods, and by magnetic force microscopy. Domain structure studies revealed that the observed domain structure had a labyrinth shape, which is typically observed in magnets, where strong exchange interactions between grains are present. The analysis of the domain structure in different states of magnetization revealed the dynamics of the reversal magnetization process.
Highlights
In the coming years, due to the development of 3-D printing technology and the creation of the first magnetic filaments [1], the interest in bonded magnets, their research techniques and the design of magnetic properties is expected to increase.Due to the reduced content of magnetic material in a volume of the bonded magnet, from the powders used to their production, the best magnetic properties are required, i.e., the greatest possible value of magnetic energy product (BH)max, coercivity j Hc, remanenceMr and getting closest to one Mr /Ms ratio
Modifications of phase composition, which relate to the proportion of basic elements used during production, can involve designing the alloy composition based on stoichiometric RE2 Fe14 B, over-stoichiometric transition metal (TM), or over-stoichiometric rare earth (RE) elements [2,3,4]
The sample for the transmission electron microscopy studies was in the form of thin films obtained by the initial wiping of the sample on abrasive papers of different gradations, followed by ion thinning using a Gatan PIPS 691 ion polisher(Gatan, Las Positas Blvd
Summary
Due to the development of 3-D printing technology and the creation of the first magnetic filaments [1], the interest in bonded magnets, their research techniques and the design of magnetic properties is expected to increase. While introducing an addition will not achieve the desired magnetic properties, it is necessary to generate a fine microstructure Such fragmentation of the structure allows the formation of exchangeable interaction between grains of both phases. Materials 2021, 14, 2849 the hard magnetic phase is desired in view of improving remanence and saturation of magnetization butRE-Fe-B simultaneously to deterioration coercivity strength [2,3,4,5,6]. Thispaper, paper,the themicro microand anddomain domainstructure structureofofananNd-Fe-B-bonded Both structures were observed through the over-stoichiometric Nd content was analyzed. The domain structure was studied, in the case of reversal magnetization, by observing the studied sample at different remanent states
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