Patent ID: 6403242
Filing Date: 2002-06-11
Classification: G11B,Y10S,Y10T

Abstract:
A magnetic recording medium comprising:a substrate; a single or multilayer underlayer deposited on said substrate; and a magnetic layer deposited above said substrate; wherein said magnetic layer comprises crystalline magnetic grains, and further wherein each grain is distinguished from other grains by an area having the same crystal orientation observed in a lattice image of said magnetic layer by a transmission electron microscope each of said grains having a grain-size defined by a diameter of a true circle having the same area as each grain, and further wherein, an average grain-size  of said magnetic grains is less than 16 nm, the average grain-size  being defined by a grain size at which an accumulated area fraction is 50%, wherein a normalized grain-size dispersion &Dgr;d/ is less than 0.5, the normalized grain-size dispersion &Dgr;d/ being defined by a ratio between a grain-size dispersion width &Dgr;d and the average grain-size , the grain-size dispersion width &Dgr;d being defined as a difference between a grain-size at which the accumulated area fraction is 75% and a grain-size at which the accumulated area fraction is 25% and wherein Kuv/kT is greater than 60, wherein Ku is a magnetic anisotropy constant defined by one half of a product of Hk and Ms, Hk is defined by a magnetic field at which a rotational hysteresis loss vanishes, Ms is a saturated magnetization of a material comprising said magnetic layer, v is an average volume of the magnetic grains calculated from the average grain size  and a thickness of the magnetic layer, k is a Boltzmann's constant, and T is absolute temperature.