Magnon softening in exchange-coupled hard-soft nanocomposites.

We study spin excitations of the fully aligned state for three-dimensional nanocomposites of exchange coupled hard (SmFeN) and soft (FeCo) phases. The dipolar interaction lowers the magnon energy and controls the spin wave gap at k = 0, which closes when the amount of soft phase exceeds a critical value. With the addition of soft phase or increasing temperature the system moves to another ground state characterized by a tilting of the magnetization at the boundaries between spins of the hard and the soft phases. [ABSTRACT FROM AUTHOR]