Investigation of the growth of garnet films by liquid phase epitaxy
Liquid phase expitaxy was investigated to determine its applicability to fabricating magnetic rare earth garnet films for spacecraft data recording systems. Two mixed garnet systems were investigated in detail: (1) Gd-Y and (2) Eu-Yb-Y. All films were deposited on Gd3Ga5012 substrates. The uniaxial anisotropy of the Gd-Y garnets is primarily stress-induced. These garnets are characterized by high-domain wall mobility, low coercivity and modest anisotropy. Characteristic length was found to be relatively sensitive to temperature. The Eu-Yb-Y garnets exhibit acceptable mobilities, good temperature stability and reasonable quality factors. The uniaxial anisotropy of these garnets is primarily growth-induced. The system is well suited for compositional "tailoring" to optimize specific desirable properties. Liquid phase epitaxy can be used to deposit Gd3Ga5012 spacing layers on magnetic garnet films and this arrangement possesses certain advantages over more conventional magnetic filmspacing layer combinations. However, it cannot be used if the magnetic film is to be ion implanted.
Simple Method of Measuring Mobility in Cylindrical Domain Materials
A simple method is described for measuring wall mobility in materials which support cylindrical domains. The mobility is determined from the initial velocity with which a domain wall responds to a field step. A sample, which is demagnetized into the stripe domain state, is subjected repetitively to a fast rise‐time pulsed field. The displacement of the stripe domain walls is observed optically as the domains adjust to the new equilibrium configuration. In the particular case of viscous damping and negligible wall mass, for a field step H0 which results in an equilibrium displacement x0, the instantaneous displacement is x=x0[1‐exp(‐ωct)], where ωc is the ratio of the restoring force constant to the damping constant. The mobility μ=x0ωc/H0. The time‐dependent displacement can be displayed graphically in a few minutes by a sampling technique. Measurements on TmFeO3 yield results in good agreement with previous data. The mobility for DyFeO3 is found to be 330 cm (sec Oe)−1.
Operational Method for Locating and Mapping Imperfections in Single‐Crystal Platelets of Rare‐Earth Orthoferrite
An instrumental technique has been devised for mapping crystalline imperfections which prevent the reliable operation of bubble‐domain devices. A special polarizing microscope permits the crystal to be automatically scanned through the field of view in a raster‐like manner. Photoelectrically detected distortions induced in a test domain by imperfections are plotted on an x‐y output of the scan. This sensitive method easily locates imperfections found with difficulty by other methods and has been used to locate crystals which have later been used successfully in devices.