Abstract
Small-angle neutron scattering is used to measure the spin-wave stiffness in the field-polarized state of the Dzyaloshinskii-Moriya helimagnet Cu2OSeO3, which is ordered below TC=58 K. The Dzyaloshinskii-Moriya interaction reflects itself in the anisotropic form of the spin-wave dispersion, εq=A(q−ks)2+gμB(H−HC2), which is seen as two round spots of the scattering intensity, though overlapping, on the left and right sides of the incident neutron beam. The spin-wave stiffness is equal to 76±1 meV Å2 at low temperatures and decreases slowly with temperature, showing softening up to 39±3 meV Å2 close to TC. The temperature behavior of A resembles that of both the archetypical helimagnet MnSi and the archetypical ferrimagnet Fe3O4, supporting the concept of strong spin interactions within Cu4 tetrahedra, representing essential magnetic building blocks of Cu2OSeO3 and thus forming its magnetic energy landscape.
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