DEPENDENCE OF MAGNETIC MEDIA NOISE ON ULTRA-THIN CR UNDERLAYER THICKNESS

Magnetic films on Cr underlayers of thicknesses below 100 angstrom show an unexpected drop in media noise. Magnetic interactions as measured by S* and delta-M are also low. However, microstructure or the films gives no evidence that physical segregation is the mechanism of exchange decoupling as is the case for underlayers above 500 angstrom. It is suggested from diffuse electron diffraction patterns, theory of heterogeneous nucleation applied to early stages or thin-film formation, and increased M(s) values for the thin Cr cases, that enhanced elemental segregation to the grain boundaries is occurring due to larger misorientation or grains. Elemental segregation gives rise to the low noise and decreased interactions. As the Cr underlayer increases in thickness, preferred columnar growth takes over and eventually results in physically segregated grains which becomes the source or decoupling and noise reduction. In between the extremes, noise maximizes between 200 angstrom and 600 angstrom.