Since a giant magnetic anisotropy of 9 meV per atom has been realized on a Pt surface, we use the kinetic Monte Carlo method to study the spin dynamics of a nanomagnet that is made by putting a line of such adatoms on a thin metallic strip so that the fixed spins are coupled very weakly and a spin-polarized current can be injected into the strip. There is a magnetization hysteresis versus the current because of the giant anisotropy. The hysteresis loop is diminished exponentially with the temperature increasing. The magnetization can be controlled by injecting a spin-polarized current.