Contribution to the spin wave theory of amorphous ferromagnets

A technique for discussing the behaviour of spin waves in an amorphous ferromagnet is presented. Whether or not the long wavelength spin waves can be clearly defined in amorphous states is discussed. From the viewpoint of the instability of the ferromagnetic ground state with respect to the formation of long wavelength spin waves, a criterion for the existence of amorphous ferromagnets is studied. The possibility of a new amorphous ferromagnet, which has a piezomagnetic effect, or which is not ferromagnetic in its crystalline state, is discussed.