Abstract
Time evolution of magnetization during a cooling process in thermally assisted magnetization reversal of rectangular MRAM cell has been numerically investigated by taking account of not only temperature variations of material parameters but also a thermal fluctuation effect. The rectangular MRAM cell with 100×150×20 nm3 in size is assumed, where the shape anisotropy dominates the switching property. The threshold amplitude of magnetic field required for a successful thermally assisted switching is decreased as the exchange stiffness constant is changed from 1×10-6 to 1×10-7 erg/cm. The time for the magnetization to relax into the bias field direction can be reduced by increasing the bias field amplitude. To switch the magnetization within 1 ns, it is found that the bias field should be larger than 165 Oe. An exchange coupling field in a ferromagnetic bilayer system is considered to be available for producing such a large bias field required for a faster switching in thermally assisted MRAMs.
