Structural and Soft Magnetic Properties of Nitrogen Added Iron Films Prepared by Sputter-Deposition

The effect of addition of nitrogen gas on the structural and soft magnetic properties of rf sputter-deposited iron films has been investigated. A nitrogen iron film possessing good soft magnetic properties, such as a large saturation magnetic flux density Bs of about 20 kG and a small coercive force Hc of about 1.0 Oe, was obtained by sputtering in Ar gas at a pressure of 3.0×10^¿3 Torr containing N2 gas at a partial pressure of between 2.5×10^¿4 and 3.0×l0^¿4 Torr. Iron nitrides such as Fe3N and Fe4N were detected in this film, and the total nitrogen content was between 3 and 5%. TEM observations confirmed that the addition of nitrogen reduces the grain size of the iron film. The coercive force of this film increased sharply at about 125°C, corresponding to the Curie temperature of Fe3N. The decrease in the coercive force in iron film with the addition of nitrogen may be attributed to the reduction of the grain size and the existence of the magnetic iron nitrides such as Fe3N and Fe4N.