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 Hc 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, Hk becomes ∼4.5 Oe. Upon further heating, H k decreases to <1 Oe at 335°C. At 350°C a new easy axis with Hc∼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 Hk are observed upon cooling in films deposited at temperatures above 200°C. Some results on anisotropy spectrum are discussed. © 1966 The American Institute of Physics.