Magnetic Properties Observed During Vacuum Deposition of Permalloy Films

Abstract

The quasistatic magnetic properties of vacuum‐deposited Permalloy films of zero magnetostrictive composition were continuously monitored during deposition and substrate heating and cooling period in an evaporator equipped with a laser‐operated Kerr magneto‐optic hysteresigraph and a quenchable substrate holder in the temperature range of −196° to ∼400°C as a function of thickness up to ∼2000 Å. Films deposited at liquid‐nitrogen temperature exhibit low (∼3 Oe) coercive force, with a very square loop, at thicknesses as low as 25 Å; this decreases rapidly with thickness increase. Films deposited at elevated temperature, for example 300°C, exhibit high (>20 Oe) coercive force with a very rounded loop when first observable at about 100‐Å thickness. This, however, plummets downward sharply near 150‐Å thickness, the loop meanwhile becoming square. The room‐temperature coercive force of films deposited at high temperatures is more than that measured during deposition, while that of films deposited at liquid‐nitrogen temperature drops as the film attains room temperature. In general, no change in H_c is observed upon exposing the fresh film to air at room temperature. The 2000‐Å low‐temperature films (deposited at −196°C) exhibit a well‐defined uniaxial anisotropy of ∼6 Oe. This anisotropy field decreases monotonically on heating after deposition. At room temperature, H_k becomes ∼4.5 Oe. Upon further heating, H_k decreases to H_c∼1 Oe is rapidly induced by the applied magnetic field along the previous hard axis. This coercivity increases to >2 Oe when the film is cooled to room temperature. Smaller changes in H_k are observed upon cooling in films deposited at temperatures above 200°C. Some results on anisotropy spectrum are discussed.