Phenomenological theory of new multiple spin density waves in fcc transition metals

The relative stability among the helical and the multiple spin density wave states in fcc transition metals is investigated on the basis of the Ginzburg-Landau free energy. Taking into account the terms up to the fourth order in magnetic moments, we have obtained the magnetic phase diagram in the space of the Landau parameters. Our diagram shows up that the phase change NM --> AF --> 3-(Q) over cap --> 3-Q with increasing volume is possible, in addition to the change NM --> AF --> Helical. Here NM, AF, 3-Q, and 3-(Q) over cap denote the nonmagnetic, the first-kind antiferromagnetic, the incommensurate 3-Q, and the commensurate 3-(Q) over cap with (Q) over cap = 2pi/a (where a denotes the lattice constant) states, respectively. The result is consistent with the prediction of the recent molecular-dynamics and the first-principles band structure calculations of gamma-Fe.