ORBITAL POLARIZATION OF THE CONDUCTION ELECTRONS IN FERROMAGNETICALLY ORDERED GDAL2

The anisotropy of the magnetic hyperfine interaction for Al-27 nuclei in ferromagnetically ordered GdAl2 is determined for T less-than-or-equal-to 0.7 T(c) using NMR on a single crystalline sphere. The pseudodipolar contribution amounts to about 12% of the dipolar contribution and depends linearly on the temperature-dependent magnetization. The temperature dependence of the quadrupolar splitting for the Al-27 a site and for magnetization oriented along the [111] direction is measured from T = 4.2 K up to the paramagnetic range. It also varies linearly with the magnetization. With the help of relativistic energy-band-structure calculations, we examine the important role of the orbital polarization of the conduction electrons in the ferromagnetically ordered state for these phenomena. These numerical results also give an explanation of the anomalies reported earlier for the Al-27 Knight shift and the Gd-157 quadrupolar splitting in the ferromagnetic state of cubic Laves-phase structured GdAl2.