The temperature dependence of coercivity in nanocrystalline Nd–Fe–B–(TiC) magnets

Abstract

TiC additions to Nd2Fe14B have been shown to enhance the control of microstructure and greatly modify the solidification behavior of the alloy. The temperature dependence of the coercivity, Hci, of the Nd2Fe14B+xTiC(0<x<6 at. %) is important for both technical applications and a comprehensive understanding of the coercivity mechanism. In addition, by studying the onset of coercivity as a function of the annealing temperature of amorphous ribbons the activation energy for crystallization may be determined. Amorphous melt-spun ribbons with x=0, 2, 3, and 6 were annealed isothermally in an Ar atmosphere at temperatures near, above and below the crystallization temperature. The activation energies Ea were determined by fitting the dependence of the coercivity as a function of annealing time and temperature to the Arrenius’ equation and found to be 18–25 kcal. The coercivity distribution functions of micro volumes of magnets were created using demagnetization and reversible magnetization curves that allowed the correlation of the coercive force with nanostructure. Maximum Hci of up to 15 kOe (3 at. % TiC) is achieved for an average grain size of 20–40 nm. The temperature dependencies of coercivity of stoichiometric Nd2Fe14B ribbons without and with additions TiC have similar character in temperature range (250–400 K) for all samples. The coercivities for nanocrystalline Nd2Fe14B magnets with TiC are more than for stoichiometric material.