Magnetic characteristics of ultrathin Fe films with Ar bombardment during and after deposition

The three kinds of Fe films, without Ar bombardment (BNON), with Ar bombardment after deposition (BAFT), and with Ar bombardment during deposition (BDUR) were prepared by dual ion beam sputtering. The relationship between the morphology and the magnetic characteristics of the Fe films has been investigated as a function of the film thickness tF in the wide range between 0.5 and 600 nm. The sputtering voltage and current were fixed at 1200 V and 50 mA, respectively. The Ar bombardments for BAFT and BDUR were carried out at the ion acceleration voltage of 200 V for the period. The features of the film growth were very different among them. The films of BNON changed from island structure to layer structure at tF between 8 and 16 nm. The films of BAFT and BDUR revealed smoother surfaces than that of BNON and were in layer structure at tF above 1 nm. However, the saturation magnetization 4πMS of BDUR abruptly decreased at tF below 8 nm, since the Ar bombardment knocked Fe atoms into the surface region of glass substrate at the initial growth stage. On the other hand, 4πMS of BNON and BAFT took almost constant value of 21.5 kG with a fluctuation of about 5%. The coercivity HC of BAFT took the minimum value among them at tF below 4 nm. These results indicate Ar bombardment after the deposition is useful for preparing the ultrathin Fe films with excellent soft magnetic properties.