Mössbauer study of orientation in γ-Fe2O3recording tapes

x-ray and electron microscope techniques have been used in attempts to determine the orientation degree of magnetic recording tapes; except for CrO2tapes, the results have not been unambiguous. We have applied the Mössbauer transmission method to evaluate quantitatively the particle orientation of γ-Fe2O3tapes. The principle involved is the intensity ratio of the middle to the outer lines of the Fe⁵⁷Mössbauer spectrum for various geometrical arrangements. The samples consist of tapes with different packing factors and various magnetic-field treatments. The observations clearly establish the degree of orientation; it is moderate. Analyses of spectra both for in-plane and out-of-plane orientations provide information on the particle morphology. The two main conclusions are the following. One: the out-of-plane deviation is determined predominantly by packing factors; it is almost independent of applied magnetic fields for the range from 0.6 to 1.4 kOe. Two: the in-plane alignment is, to some extent, improved by applying a magnetic field.