Magnetic Properties of Eu

Additional data on the magnetic properties of the rare-earth metal Eu have been obtained from neutron diffraction data utilizing an improved powder sample consisting of metal filings. Previous diffraction data on Eu, obtained from a rolled metal foil sample, indicated that the metal became antiferromagnetic at a Néel temperature of 87°K. Information regarding the magnetic moment could not be obtained from the metal foil since the diffraction peak intensities indicated the sample had a preferred orientation; also, the magnetic structure determination was uncertain. The present data verify the transition to an antiferromagnetic state below 91°K which consists of a helical spin structure with the magnetic moments lying parallel to a cube face and with the screw axis directed perpendicular to the moments or along the [100] direction. This structure is based upon the facts that the diffraction data show a single pair of magnetic satellite reflections equally spaced in reciprocal lattice space about each nuclear reflection and, in particular, the [000±] reflection from the magnetic cell is observed. Information regarding the period of the helical structure was obtained from the separation of the satellite reflections. The separation was observed to change very little with temperature and corresponds to a period of 3.5a at T/TN = 1 and increases to 3.6a at T/TN = 0.05, where a is the lattice spacing. The intense [000±] magnetic reflection occurring at a scattering angle of 4.8° permits a calculation of the ordered magnetic moment in Eu. If one takes the magnetic form factor equal to 1 at the above small scattering angle, the experimental saturated ordered moment is 5.9±0.4 μB. Assuming that the magnetic constituent of metallic Eu is a Eu++ ion and is, therefore, characterized by an 8S7/2 state having spin only, the theoretical ordered moment should be gJ = gS = 7 μB. The smaller value of the measured ordered moment as compared to the maximum theoretical value is also characteristic of other rare earth metals. Data on the product of magnetic moment times magnetic form factor (μf) can be obtained from the magnetic satellite diffraction peaks occurring at various scattering angles. These values from Eu are in reasonable agreement with similar values of μf obtained from the compound EuO in earlier work. The intensity of the magnetic diffraction peaks as a function of temperature deviates from the usual Brillouin pattern. Instead, the magnetic intensity variation with