Microstructure and Magnetic Properties of Cobalt - Thin Films for Magnetic Recording.

Correlations between the microstructure and magnetic properties of various Co-based thin films for magnetic recording have been investigated. It has been found that the grain size and texture of the Cr underlayers are strongly dependent on their thickness and substrate conditions. For Cr underlayers sputtered on 300^circ C heated and -200 V biased NiP/AlMg substrates, the grain size increases monotonically with the layer thickness. The texture of the layer changes from no texture ( ~100 A thick) to (001) fiber texture (200 -2000 A thick), and then to the (011) fiber texture. An epitaxy of {11| 20} _{rm CoNiCr}// {001}_{rm Cr} and (0002) _{rm CoNiCr} //[ 1| 10] _{rm Cr} is experimentally found for a CoNiCr (500 A)/Cr (2000 A) bi-layer. This kind of epitaxy allows the c axis of the grains of the hcp magnetic film to lie in the plane of the film and provides the desired in-plane anisotropy required for high density longitudinal recording. Results show that substrate (NiP/AlMg) heating and bias have strong effects on the microstructure and magnetic properties of Co_{86} Cr_{12}Ta _2 films. Coercivity can be increased from 720.5 Oe for films with non-substrate heating and bias to 1425 Oe for films with both 280^circ C substrate heating and -250 V bias. It seems that substrate heating and bias can enhance the surface mobility of adatoms during sputter deposition of the films and increase the grain size. A 280^circC substrate heating is high enough to form a continuous film. Well -packed equiaxed grains with low stacking fault density of the continuous film correspond to high coercivity and squareness. It has been found that media signal to noise ratio (SNR) can be enhanced by going from single CoNi layer films to multilayer films separated by Cr isolation layers. Lorentz microscopy studies have been carried out on a 500 A thick Co_{60.69}Ni_ {32.1}Cr_{7.21} film using Fresnel and Foucault imaging modes in a conventional TEM. The film is fcc in structure and the average grain size is about 70 A. The film in the demagnetizing state shows an elongated ripple domain structure with the domain width about 1000 x larger in dimension than that of grain size, which indicates the strong intergranular magnetic interaction of this film. (Abstract shortened by UMI.).