Crystal structure and magnetic properties of hard magnetic Sm2Fe17Nδ thin films with Co substitution

The crystal structure and magnetic properties of the hard magnetic Sm-2(Fe1-xCox)(17)N-delta thin films prepared by dc magnetron sputtering and subsequent nitrogenation process were investigated. It is found that the N content and crystal structure determine the non-monotonic dependence of the coercivity H-C on nitriding temperature for the films with x = 0. With nitriding temperature exceeding 300 degrees C, N atoms can enter the Sm2Fe17 phase and the N content increases with increasing nitriding temperature, which leads to an increased coercivity. However, the maximum value of the HC is observed at 400 degrees C. The alpha-Fe soft phase appears with nitriding temperature further increasing to 500 degrees C, which is responsible for the decreased HC. When x is between 0 and 0.36, the films exhibit single Th2Zn17-type structure. Co atoms are found to go into the lattice of the 2: 17 phase, generating an enhanced exchange coupling interaction between the nano-grains, which is responsible for the improved hard magnetic properties of the films with Co substitution at a certain range. Especially, the optimal value of the coercivity H-C and remanence ratio MR/MS reaches 4.0 kOe and 0.70 for the films with x = 0.17 and 0.36, respectively. (c) 2008 Elsevier B. V. All rights reserved.