Magnetic recording apparatus and method of designing the same

A method of designing a magnetic recording apparatus including a magnetic recording medium having a magnetic recording layer, a heater configured to heat the medium and a magnetic head configured to apply a magnetic field to the medium, comprising:

• determining a stable retention time tst for recorded magnetization at room temperature and a thermal-fluctuation stability coefficient βst at room temperature calculated from a thermal-fluctuation stability coefficient β(T) at an absolute temperature T, expressed by the following equation:
• β(T)=KuV/kBT,
• where Ku is a magnetic anisotropy energy density, V is an activation volume, and kB is Boltzmann's constant;
• obtaining an equivalent degradation time tEQ calculated from the following equation:
• tEQ=Σ(ΔtEQ),
• that sums values of ΔtEQ within a given period of time Δt for a time span during which the medium is kept at a temperature at which the recorded magnetization is substantially degraded, where ΔtEQ is defined by the following equation:
• ΔtEQ =exp(1n(Δt)−β−βst),
• where β is a thermal-fluctuation stability coefficient for a medium temperature T in the period of time βt;
• and
• determining specification of the magnetic recording medium, the heater and the magnetic head in a manner to meet the relationship of tEQ<tst between the stable retention time tst for recorded magnetization at root temperature and the equivalent degradation time tEQ.