Invariant incommensurate coherence length in spin-density-wave excitation of Cr0.99Fe0.01

Low-energy magnetic excitation of spin-density wave (SDW) was measured using a single crystal of Cr0.99Fe0.01 by cold neutron triple-axis spectroscopy. Because of the unchanged incommensurate Q and the constant line width in 2.5 <= h omega <= 6 meV, the magnetic excitation could not be explained with a conventional dispersion of h omega(q) alpha q. Here, we conjectured the presence of standing waves, which would be excited in local spin matrices. The effectively vertical dispersion was attributed to the longitudinal spin fluctuation in the spin matrices. A series of low-energy magnetic excitations in Cr alloys could be understood with the coexistence of the standing waves and progressive waves such as spin waves.