Dependence of magnetic media noise on ultra-thin Cr underlayer thickness

Magnetic films on Cr underlayers of thicknesses below 100 Å show an unexpected drop in media noise. Magnetic interactions as measured by coercive squareness and δM are also low. However, the microstructure of the films gives no evidence that physical segregation is the mechanism of exchange decoupling, as is the case for underlayers above 500 Å. It is suggested from diffuse electron diffraction patterns, the theory of heterogeneous nucleation applied to early stages of 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 of 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 of decoupling and noise reduction. In between the extremes, noise maximizes between 200 Å and 600 Å