Uniaxial Thin Films Research Articles

Magnetization of uniaxial cylindrical thin films : H. J. Kump and T. G. Greene, IBM Journal, April 1963, p. 130

Magnetization of uniaxial cylindrical thin films : H. J. Kump and T. G. Greene, IBM Journal, April 1963, p. 130

Effect of Substrate Cleanness on Permalloy Thin Films

The use of mechanical and chemical cleaning techniques in the production of a clean, random, and smooth microslide glass substrate surface for the vacuum deposition of uniaxial thin Permalloy film elements has been studied. The principal cleaning techniques intensively investigated were: (1) a mild detergent wash followed by a vapor degreasing cycle in isopropyl alcohol; (2) a chalk paste scrub followed by an ultrasonically agitated distilled water rinsing cycle and a forced hot air drying process; and (3) hydrofluoric acid etching followed by a distilled water rinsing cycle and a forced air-drying process. The surface condition of the cleaned microslide glass was assessed with electron micrographs of preshadowed carbon replicas (magnification 88 000×). The micrographs show that the chalk-cleaned glass substrate has the smoothest surface. The variously cleaned substrates were then used for the vacuum deposition of 1700-A 4-mm-diam Permalloy film elements (melt composition 83% nickel, 17% iron). This work was carried out in a 10−6 mm Hg vacuum system. Twenty-five evaporations were made with a total of 54 elements per evaporation. The Permalloy film elements deposited on the differently cleaned glass substrates were then examined by means of a 1000-cycle hysteresis loop apparatus and the following measurements were made: (1) coercive force HC; (2) saturation flux φs; (3) orientation of the anisotropy axis θ; (4) magnetoelastic strain coefficient η; and (5) anisotropy field HK. Dispersion measurements of the easy axis were made on a 1000-cycle crossed field hysteresis loop apparatus. Measured in this manner, the chalk-cleaned glass substrates yielded consistently the lower average value of HC; i.e., 1.4 oe. The average value of HK for the three different cleaning techniques was 2.5 oe. Within the total range of values of coercive force and the anisotropy field, the chalk-cleaned and the acid-etched glass substrates yielded the same values; i.e., HC±0.2 oe, HK±0.3 oe. Measurements of angular dispersion varied from 8° to less than 2° with an average value of less than 3°. The chalk-cleaned substrates yielded the lowest values of angular dispersion.

Observations of the magnetization reversal process in thin films of nickel-iron, using the Kerr magneto-optic effect

Observations of the magnetization reversal process in uniaxial thin films of nickel-iron about 1500 A thick are reported. The experimental techniques used involve the comparison of measurements made in a Kerr magnetooptic apparatus, with the 400 c/s hysteresis loops taken with the pick-up loop both along and at right angles to the applied field. The results suggest that the magnetization reversal process in a film orientated with its easy axis at an oblique angle to the applied field occurs in three stages: (i) coherent rotation until the angle is reached where a discontinuous jump in the orientation of the magnetization is expected to start; (ii) domain nucleation and growth from this angle to the angle where the jump should finish; (iii) coherent rotation until the magnetization lays along the field. The way in which some actual films differ from this model is discussed.

Magnetization Reversal in Uniaxial Films near to the Preferred Direction

It is now well known that uniaxial thin magnetic films can be made which have almost ideal square hysteresis loops in the preferred direction and almost straight line hysteresis loops in the hard direction. For this type of film, which can be prepared by evaporation from ingots of approximately 81:19 NiFe alloy, it is found that the switching time constant of the reversal process which occurs when magnetic fields are applied exactly in the easy direction can be very large. The switching process occurring when fields are applied at angle 10° to the preferred direction has been studied in detail, both by a new pulse response technique and by observation of the domain structure revealed by use of the Kerr magneto-optic effect. In the latter experiment, short pulses have been applied to the specimen and photographs taken of the domain pattern after each pulse. It was found that the specimen breaks into small domains whose area increases after each pulse and that eventually the filmcould be completely reversed if the pulse amplitude was between certain critical values. Curves were plotted of the pulse amplitude against the proportion of the film switched found by measuring the reversed area in the photographs. It was shown that the process is very well approximated by an equation of the form Sw = τ(H − H0),which implies a viscous damped process, and there is a critical nucleation field, which is less than the field required to move the walls. In the pulse response experiments, the switching time has been derived from the response to a reset pulse which was applied after a variable number of set pulses of variable amplitude. It was found that in some films there can be a rapid switching process, which is complete after about 100 mμsec, followed by a slow process lasting up to 10 μsec under the same conditions. From the experiments performed, it has been possible to compute a switching time constant which can be very large in some films. This constant is found to be correlated with the ratio p = Hc/Hk, where Hc is the coercivity in the easy direction and Hk is the rotational coercivity. If the film obeyed the simple coherent rotational model the pratio would be 1, and films which have p = 0.9 have been found have Sw = 0.3×10−6 oe μsec, whereas for p = 0.3, Sw = 7×10−6 oe μsec.

Magnetization Reversal by Rotation and Wall Motion in Thin Films of Nickel-Iron Alloys†

ABSTRACT The magnetization reversal process in specially prepared uniaxial thin films of nickel—iron alloy is studied by measurements of the 400 c.p.s. hysteresis loops. The results indicate that both coherent rotation and domain wall motion can occur in the same film, but in different proportions according to the orientation of the anisotropy axis with respect to the applied field and the thickness of the film. Special properties of these films are discussed for fields applied normal to the anisotropy axis.

On the theory of the domain structure of thin films of magnetically uni-axial materials

The demagnetizing energy is calculated of a, simple model of the domain structure of a magnetically uni-axial thin film, the axis of easy magnetization of which is perpendicular to the surface. The width of the domain, and for the case of MnBialso the total energy of the domain structure, are found as functions of the thickness of the film.