  The concept of anisotropy of spin relaxation in non-magnetic metals with
respect to the spin direction of the injected electrons relative to the crystal
orientation is introduced. The effect is related to an anisotropy of the
Elliott-Yafet parameter, arising from a modulation of the decomposition of the
spin-orbit Hamiltonian into spin-conserving and spin-flip terms as the spin
quantization axis is varied. This anisotropy, reaching gigantic values for
uniaxial transition-metals (e.g. 830% for hcp Hf) as density-functional
calculations show, is related to extended "spin-flip hot areas" on the Fermi
surface created by the proximity of extended sheets of the surface, or
"spin-flip hot loops" at the Brillouin zone boundary, and has no theoretical
upper limit. Possible ways of measuring the effect as well as consequences in
application are briefly outlined.
