Intrinsic Nonlinear Ferromagnetic Relaxation in Thin Metallic Films. A large fraction of the world's information is stored magnetically. Typically, the mechanism for storing this information is to apply a sufficiently large magnetic field to a ferromagnetic material (magnetic tape or disk) and thus cause the material's magnetization to align with the field direction. This will decrease the magnetostatic energy. This presents the question of where did the energy go? We have proposed a mechanism for this relaxation that dominates competing mechanisms for the technologically important case of high magnetization materials subject to large rotations. We show that decay of 2 uniform magnons (waves of magnetization) into 2 non-uniform magnons is initiated by the so-called thermal magnons that are always present at everyday temperatures. This decay then rapidly escalates to transform the magnetostatic energy into exchange energy (the energy caused by the misalignment of two neighboring atoms). The resultant insight may provide clues about how to write materials more quickly and thus increase data rate within information storage devices. [A. Yu. Dobin and R.H. Victora, Phys. Rev. Lett. 2003, 90, 167203.]