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

The crystal structure and magnetic properties of the hard magnetic Sm2(Fe1−xCox)17Nδ 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 HC on nitriding temperature for the films with x=0. With nitriding temperature exceeding 300 °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 °C. The α-Fe soft phase appears with nitriding temperature further increasing to 500 °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 HC and remanence ratio MR/MS reaches 4.0 kOe and 0.70 for the films with x=0.17 and 0.36, respectively.