Sensitive magnetic readback head-disk spacing measurements in recording drives

Sensitive magnetic readback techniques have been developed to measure the absolute physical head-disk spacings (HDS) in recording drives and at component level. The key concept involves writing constant frequency coherent transitions in a wide enough radial band so that the trade misregistration effects on amplitude are removed. In this band, the amplitude is measured versus pressure or velocity. Flying height dependencies an pressure or velocity are determined by air bearing modeling and by optical measurements, and HDS is calculated. The amplitude-pressure and amplitude-velocity techniques have HDS resolution of 0.2 and 1.5 nm, respectively. Their applications to measurements of HDS distribution in drives, HDS radial dependence, environmental effects on HDS and error rate based parametrics versus HDS are demonstrated