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⩽ℏω⩽6 meV, the magnetic excitation could not be explained with a conventional dispersion of ℏωq∝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.