Abstract: The melt-spun Nd8Fe85Nb1B6 ribbon was prepared by the single roller method with the tangential speed of 20 m/s. A mixture of Nd2Fe14B and alpha -Fe phases with the average crystalline grain size of about 20 nm was found to exist in the as-quenched ribbons. The initial magnetization curve of the nanocomposite Nd8Fe85Nb1B6 ribbon can be divided into four sections by the inflection points on it. The magnetically hardening mechanism corresponding to each section was investigated. The initial susceptibility of the Nd8Fe85Nb1B6 ribbon is higher than that of the Nd15Fe85B9 powder, which may be attributed to the reversible magnetization rotation in the central region not influenced by the exchange-coupling effect within the alpha -Fe grains. The above-mentioned magnetization rotation leads to the formation of equilibrium 180 deg. domain walls at the boundaries of the alpha -Fe grains. With the increase of applied field, these domain walls are compressed reversibly towards the Nd2Fe14B grains and eventually invade into them. The irreversible movement of the domain walls in the Nd2Fe14B grains accounts for the steepest growth of magnetization with the applied field. Finally, the magnetically inhomogeneous "core regions" are formed in the Nd2Fe14B grains, and the magnetization rotation in these "core regions" indicates the end of the whole initial saturation process.

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