Abstract
The effect of different addition of carbon on the structural and magnetic properties of the sintered Nd_14.60Tb_0.20Fe_balTi_1.24B_6.40 permanent magnet material are investigated by means of scanning electron microscopy (SEM), differential scanning calorimetry (DSC), Mösssbauer spectroscopy (MS) and microhardness (HV). The results confirm that carbon increases the values B_Hf of the hyperfine magnetic fields and the Curie temperature (T_C) of the investigated permanent magnet material. The B_Hf parameters and the T_C for 0.12 wt.% C addition are the same as those observed for the permanent magnet material without Ti. An addition of 0.12 wt.% C improves the values of B_r, (BH) _max and the corrosion resistance only slightly reducing the H_c. The influence of ageing temperature on the H_c, the microhardness (HV) and the Mössbauer parameters line width (G) is also presented. It is suggested that the mechanism of the H_c changes during ageing is limited by relieving the internal stresses in the main phases and by changes of the microstructure in a nanoscale region.

Key words
intermetallic, microstructure, magnetic properties, microhardness, Mössbauer spectroscopy

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