Magnetic excitations in chromium. II

Abstract

Neutron scattering measurements on pure chromium metal have been performed under various conditions of experimental resolution, energy transfer, temperature, and magnetic field. The temperature and energy dependence of the commensurate-diffuse scattering surrounding the (0,0,1) point in reciprocal space has been followed from the spin-flip temperature ($T_{\mathrm{sf}}$=122 K) to temperatures as high as 700 K, well above the Néel point ($T_N$=312 K). Magnetic correlations extending over 11 bcc unit cells persist to these high temperatures. The spectral width of the magnetic scattering is found to increase rapidly with temperature above $T_N$. The importance of the commensurate-diffuse modes of excitation in the disappearance of the long-range-ordered spin-density-wave (SDW) state at $T_N$ is discussed. The magnetic field dependence of the excitations in the transversely polarized SDW phase has been investigated and found to be absent. Evidence is also presented for the absence of a spin-wave energy gap greater than 50 μeV. We have placed the scattering in the paramagnetic phase on an absolute scale by normalizing to the integrated intensities of selected phonons, and have estimated an effective magnetic moment per atom.