A thin film‐of zinc octakis (β‐octyloxyethyl) porphyrin (ZnOOEP) is capable of trapping and detrapping charge in an appropriate electric field under irradiation. An effective charge capacity of the order of 30 μC/cm2 or 1018 charges/cm3 was obtained with sandwich structures of ITO/ZnOOEP/ITO (where ITO is indium tin oxide) under a bias of 10 V with irradiation. Cells with the configuration ITO/normalZnOOEP/SiO2/normalSi were also fabricated. When an electric field was applied across this cell in the dark, a small amount of charge was stored, as in a conventional capacitor. However, the charge stored under the same conditions with irradiation of the photoconductive ZnOOEP was three orders of magnitude higher. Trapped charge produced under illumination was not removed under short‐circuit conditions in the dark, suggesting that this phenomenon could be used for information storage.

A thin Ni-Fe film, having a uniaxial magnetic energy of the form EK = K sin2θ, usually exists as a single domain. If a magnetic field of sufficient magnitude is placed perpendicular to the easy axis of magnetization and then removed, the film splits into a large number of 180° domains. When this simple multidomain structure occurs, it is theoretically possible to excite two ferromagnetic resonance modes by applying a small magnetic field perpendicular to the easy axis. The first of these, a low-frequency mode (0–10 Mc/sec) is excited by an rf field perpendicular to the domain walls; and the second, a high-frequency mode (0–25 Gc/sec) is excited by an rf field parallel to the domain walls. The high-frequency mode has been observed in a number of films having anisotropy fields from 3–5 Oe. The experimental results are compared with theoretical relations for frequency as a function of applied field. In addition, it is possible to estimate the domain wall separation from measurements of the high-frequency mode. These measurements indicate that typical domain widths range from 30 to 50 μ. A difference is observed in the position of the absorption peak when measured in an increasing field than when measured in a decreasing field. This hysteresis is explained by the Bloch-Néel wall transition theory which was used to explain the constricted M-H loops. Attempts to observe the low-frequency mode were not successful.

Ferromagnetic resonance in thin films has been extended to the radio-frequency region of from 1–20 Mc. Theoretical expressions governing this resonance condition are given along with experimental results. It is found that resonance in this region affords an excellent means of measuring the anisotropy field Hk. Films with compositions near 80% Fe—20% Ni were studied by this technique. The anisotropy field of these films was found to be around 5 oe. The width of the absorption line varied from 0.6 to 2.4 oe, depending on the composition of the film. The minimum linewidth was found to occur for the composition of minimum magnetostriction.

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