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(Fe_1−xCo_x)₁₇N_δ 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 °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 H_C 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 H_C. 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 M_R/M_S reaches 4.0 kOe and 0.70 for the films with x=0.17 and 0.36, respectively.     

Effect of sputtering process on magnetic properties and crystal structure of Sm2Fe17Nx thin films

Hard magnetic Sm₂Fe₁₇N_x thin films were prepared by dc magnetron sputtering and subsequent nitrogenation process. The results show that the sputtering parameters determine the film composition, which determines the crystal structure and magnetic properties. When the gas pressure varies from 1.2 to 2.1 Pa and power varies from 40 to 60 W, higher Sm content (>11.3 at%) is obtained, giving rise to improved coercivity H_C and remanence ratio M_R/M_S. The optimal H_C of 2127.8 Oe and M_R/M_S of 0.53 are obtained when the gas pressure and power reach 1.2 Pa and 50 W, respectively. In addition, it is found that the pure single Sm₂Fe₁₇ phase can be observed when the ratio of Fe/Sm exceeds 7.1 by controlling the sputtering parameters to adjust the composition.