Patent ID: 7457064

Claim:
A magnetic recording medium comprising a substrate and a perpendicular magnetic layer formed on the substrate, characterized in that, when: a magnetization curve A is measured through the following steps A1 to A4: A1 applying a magnetic field large enough to saturate magnetization of the perpendicular magnetic layer in the negative direction, A2 applying various magnetic fields H in the positive direction, A3 measuring magnetization M after removing the magnetic fields H, and A4 obtaining a magnetization curve A using the measured magnetization M as a function of the H; a magnetization curve B is measured through the following steps B1 to B5, B1 applying a magnetic field large enough to saturate magnetization of a perpendicular magnetic layer in the positive direction, B2 applying a magnetic field which makes remanent magnetization −M r /2 in the negative direction, M r being an absolute value of remanent magnetization of the perpendicular magnetic layer, B3 applying various magnetic fields H in the positive direction, B4 measuring magnetization M after removing the magnetic fields H, and B5 obtaining a magnetization curve B using the measured magnetization M as a function of the H; a demagnetization factor N d is obtained from the following equation, where H a is an external magnetic field applied at an intersection between the magnetization curve A and M=−M r /2, and H b is an external magnetic field applied at an intersection between the magnetization curve B and M=0; N d =  H a - H b  M r / 2 σh sw is determined from the following equation, where H c and σH sw are an average value and a standard deviation, respectively, of magnetization switching fields H sw , a cumulative probability distribution function of the magnetization switching fields H sw being represented by a magnetization curve A′ obtained by making shearing correction on the magnetization curve A using the demagnetization factor N d ; and σ h sw =σH sw /H c D n is determined from the following equation, where N d is the demagnetization factor and t mag is a film thickness of the perpendicular magnetic layer; D n = t mag ⁢ 1 - N d 2 N d the σh sw and the D n satisfy inequalities σh sw /27+D n /90<1, and D n >20.