Systematic study of the dependence of magnetic and structural properties of Nd2Fe14B powders on the average particle size

A systematic study of the magnetic and structural properties dependence on the particle size was realized. For this, commercial NdFeB powder was separated into five different mean particle sizes using sieves. Besides, from the original powder, eleven samples were also produced by mechanical milling assisted by surfactant, using various milling times. A total of sixteen samples were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), vibrating sample magnetometry (VSM), and Mössbauer spectrometry (MS). The particle sizes of the samples vary from the micrometer to the nanometer scale. The crystallite size decreases with decreasing particle size. XRD result indicates that the Nd2Fe14B phase is found in all the samples, and the presence of this phase is also corroborated by MS using six sextets for fitting their spectra, with an additional singlet corresponding to the Nd1.1Fe4B4 phase. The mean hyperfine magnetic field increases with increasing particle size because the magnetic dipolar interaction between the magnetic moment of the particles increases with particle size. From the VSM measurements the magnetic energy density (BH)max values were calculated for different particle sizes, and their maximum value of 34.45 MGOe is obtained for the sample with the particle size of 60 μm.