Exchange coupled magneto-optic layers

It is shown that it is possible to separate the storage function from the readout function by exchange coupling two layers, one with high magnetooptical rotation (readout layer) and the other with the coercivity and other properties necessary for small stable bits (storage layer). An investigation is described of the extent of coupling between a storage layer of Nd₁₀Tb₂₀ (FeCo)₇₀ with H_c=5.4 kG and θ_K=17 min and several readout layer compositions with H_c⩽1 kG and θ_K of about 30 min. It is found that the exchange coupling is weak unless both films have perpendicular easy axis anisotropy. The effect of varying the thickness of the readout layer was studied, keeping the storage layer thickness fixed. Coupled films with a coercivity of 1.7 kG and a θ_K of 33 min have been made. The rotation is about twice that of the storage layer alone, and the coercivity is over three times that of the readout layer alone