Abstract
Magnetic behavior of the system with a helical spin structure is studied. Hubbard's Hamiltonian is transformed using new operators which indicate that the spin quantization axis at each lattice site is canted with an order of the helical spin configuration. The dynamical transverse susceptibility is studied by means of the double-time two-particle Green function. The equation of motion of this Green function is truncated by RPA decoupling principle. In the ferromagnetic limit, the result is reduced to the well-known one derived by Izuyama, Kim and Kubo. Collective excitation spectra of this system are obtained from χ-1-+(q, Q, ω) = 0 both in the narrow-band (large-gap parameter) approximation and in the wide-band (small gap parameter) approximation. In the itinerant antiferromagnetism, the result is reduced to the sound-like dispersion relation “\hbarω∝qA(Q)” in general. In the ferromagnetic limit (Q →0), the well-known spin wave spectrum “\hbarω∝q2·B(Q)” is also obtained.
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