Coercive Sm2Fe17N3: A model pinning system created by heavy ion irradiation

Swift high energy (5 GeV) Pb ion irradiation has been employed to create de fects in the high performance permanent magnet material Sm2Fe17N3. Total io n fluences in the range from 10(11) to 2 X 10(13) ions/cm(2) were studied. In Mossbauer spectra at 26 and 300 K, both a paramagnetic doublet and a bro ad ferromagnetic contribution characteristic of an amorphous or strongly di sordered phase are found to be induced by irradiation. Magnetization revers al was studied and coercivity is found to increase upon irradiation, up to fivefold at 5 K (mu(0)H(c) = 1.5 T) for the highest ion fluence. Initial ma gnetization curves of the irradiated samples are characteristic of material with a pinning type coercivity mechanism with a maximum initial depinning field of 0.4 T for the highest fluence. Magnetization measurements made par allel and perpendicular to the ion beam direction suggest that the defects created are highly anisotropic in shape. The temperature dependence of the coercivity has been analyzed within the framework of the Gaunt model of dom ain wall pinning. (C) 1998 American Institute of Physics. [S0021-8979(98)19 811-0].