Polarization Dependence of the Magnetic Fluctuations in {{Cr}} below ${T}_{N}$

We have investigated the magnetic excitations in single-Q, single-domain Cr below TN using polarization analysis of inelastically scattered neutrons for energy transfers up to 18 meV. The results show that the longitudinal (L) magnetic modes are enhanced below $\simeq$8meV with respect to the transverse (T) modes at low temperature. The latter are independent of the polarization with respect to the ordering vector Q$′\pm$ in the transverse spin-density-wave phase, i.e., they are isotropic. The L and T modes are not affected by the spin-flop transition to the longitudinal spin-density-wave phase at Tsf=121K indicating that the transition is due to anisotropies and that it is not an intrinsic feature of the spin-density wave. There are indications that the L modes have a less steep dispersion curve and are more damped than the T modes in accordance with the three-band model by Fishman and Liu. With increasing temperature the intensity from the T and L modes increases strongly at small E transfer and their E dependence becomes similar. In particular, the enhancement of the L modes with respect to the T modes vanishes. Significant inelastic scattering is present at the silent peak positions. It surpasses even the scattering at the allowed peak positions at large E transfers. We argue that the silent inelastic scattering is partly responsible for the ``commensurate'' scattering at the (100) position due to resolution effects and that the major cross section at (100) is due to the longitudinally polarized Fincher-Burke mode at 4.2 meV.     «

We have investigated the magnetic excitations in single-Q, single-domain Cr below TN using polarization analysis of inelastically scattered neutrons for energy transfers up to 18 meV. The results show that the longitudinal (L) magnetic modes are enhanced below $\simeq$8meV with respect to the transverse (T) modes at low temperature. The latter are independent of the polarization with respect to the ordering vector Q$′\pm$ in the transverse spin-density-wave phase, i.e., they are isotropic. The L...     »