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Investigation Of The Structural And Magnetic Properties Of Thin Ferromagnetic Films

Report Number: WADD TR 60-787 Part II
Author: Baltz, A.
Author: Doyle, William
Corporate Author: Franklin Institute
Laboratory: Directorate of Materials and Processes
Date of Publication: 1963-03
Pages: 65
Contract: AF 33(616)-6298
Project: 7371
Task: 727103
AD Number: AD0403892

Permalloy films evaporated at normal and oblique incidence to a substrate were examined by replication of their surfaces. Electron micrographs revealed chains of particles perpendicular to the incident beam when the angle of incidence was <70 ° and parallel to the incident beam when the angle was >70 ° degrees. The degree of alignment depended upon the angle of incidence and thickness of the film. A statistical analysis of the micrographs was made.

Permalloy films were epitaxially grown on NaCl and were annealed by electron bombardment in an electron microscope. Perfect single crystal diffraction patterns indicated the presence of [100] parent crystals and [122] twin crystals. Fringe patterns observed on electron micrographs were identified by dark field microscopy and electron diffraction as being caused by platelets of twins 100-400 Å thick, lying parallel to {111} planes of the parent crystal. The non-integral reflections were shown to be caused by double diffraction.

The angular dependence of the torque in Permalloy films has been studied. In films with h<sub>c</sub>, the ratio of coercive force to anisotropy field, less than 0.5, the results agree very well with the formulas for magnetization reversal in an infinite cylinder. When h<sub>c</sub>>0.5, the situation appears very complex. The unidirectional hysteresis observed in this range can be understood very well if the existence of regions with negative anisotropy is assumed. Various methods of determining the anisotropy have been compared and a torque technique for measuring dispersion in both magnitude and direction developed. The anisotropy found in films as a function of the angle of incidence of the evaporation beam and the anisotropy in epitaxially grown films is reported. Finally the use of a vibrating sample magnetometer to determine the hysteretic properties of thin films is discussed

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