Abstract
Co-rich Nd-Fe-B nanocomposite ribbons with Tb substituted have been fabricated by single roller melt spinning technique of Nd4-xTbxFe83.5Co5Cu0.5Nb1B6 (x = 0, 0.2, 0.4, 0.6, 0.8 and 1) alloys in an argon (Ar) atmosphere at a circumferential speed of 40 m/s. According to the differential scanning calorimeter (DSC) traces the nanocomposite samples have been annealed at different temperatures like 675°C, 687°C, 700°C, 712°C and 725°C for 10 min. Crystallization behavior was studied by X-ray diffraction in which it was found that the XRD patterns are characterized by broad diffused pattern which demonstrate the amorphous state of materials. The ribbon samples were also characterized by vibration sample magnetometer (VSM) and Mossbauer spectroscopy at as-cast and annealed condition. Co-rich and Tb substitution has significantly enhanced the value of coercivity (Hc) and maximum energy product (BH)max. Highest value of Hc and (BH)max has been obtained as 2.36 kOe and 6.11 MGOe for the sample annealed at 700°C for 10 min with higher concentration of Tb. The M-H hysteresis loops show extremely soft natures which do not possess any area. We have found reduced remanent ratio (Mr/Ms) up to 0.49 at optimal annealing temperature 700°C. However, with the annealing of the samples in the above mentioned temperature, evolution of large coercivity was observed due to the formation of exchange couple hard and soft nanocrystal composites. We have investigated the variation of Curie temperature (Tc) with annealing temperature of the melt spun ribbon samples. Mossbauer spectroscopy was carried out to study the hyperfine parameters such as hyperfine field, hyperfine field distribution for full width half maximum (FWHM) and isomer shift of Fe species of these two phases.
Highlights
The Nd-Fe-B based nanocomposite materials, so-called exchange spring magnets, have attracted many scientists by virtue of their large potential in practical application [1]
Co-rich and Tb substitution has significantly enhanced the value of coercivity (Hc) and maximum energy product (BH)max
According to the crystallization temperatures differential scanning calorimeter (DSC) traces, the nanocomposite samples have been annealed at 675 ̊C, 687 ̊C, 700 ̊C, 712 ̊C and 725 ̊C for 10 min
Summary
The Nd-Fe-B based nanocomposite materials, so-called exchange spring magnets, have attracted many scientists by virtue of their large potential in practical application [1]. One of the problems of the NdFe-B based exchange spring magnetic system is the formation of the large crystallites, which degrade the exchange spring effect and reduce coercivity of the material The crystallites in this kind of materials can be refined by Nb-addition. With an appropriate concentration of Nb, the crystallites can be formed more identically in nanometer scale improving exchange spring effect and the coercivity can be enhanced due to the separation of the magnetic crystallites by Nbboundaries. These lead to better performance of the Nd-Fe-B based exchange spring magnets.
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