The quasi-static magnetic properties of vacuum-deposited Permalloy films of zero-magnetostrictive composition are examined in situ in an evaporator equipped with a laser-operated Kerr magneto-optic hysteresigraph. The coercive force, which depends strongly upon the film thickness, is large (Hc > 20 Oe) when the hysteresis loop is first observable with a thickness of ∼50 Å for low substrate temperatures (T < 50°C) and ∼100 Å for high substrate temperatures (T > 100°C). There are two peaks of coercivity, at ∼400 Å and ∼1000 Å; the two are thought to be related, respectively, to the transitions from the Néel to the cross-tie walls, and from the cross-tie to the Bloch walls. Two distinct components of the uniaxial anisotropy field are identified, both of which are characteristic of fabrication parameters: K1, which is difficult to re-orient once the anisotropy is induced; and K2, which is readily re-oriented (with time constant less than 10 sec) along any angle between the easy and the hard axis. The net anisotropy field and the easy-axis orientation, both of which are affected by the K2 components, can be calculated for a given set of fabrication parameters. Experimental results agree well with the calculated values. The angular dispersion does not appear to be affected by the amplitude of the orienting field H or the nature of the field (a.c. or d.c.) when H > Hc. There is a slight increase in angular dispersion as the K2 component of the anisotropy rotates from the easy to the hard axis.
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IBM Journal of Research and Development
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06 April 2010
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