  We show that Pb and Bi adatoms and dimers have a large tunneling anisotropic
magnetoresistance (TAMR) of up to 60% when adsorbed on a magnetic
transition-metal surface due to strong spin-orbit coupling and the
hybridization of 6p orbitals with 3d states of the magnetic layer. Using
density functional theory, we have explored the TAMR effect of Pb and Bi
adatoms and dimers adsorbed on a Mn monolayer on W(110). This surface exhibits
a noncollinear cycloidal spin spiral ground state with an angle of 173$^\circ$
between neighboring spins which allows to rotate the spin quantization axis of
an adatom or dimer quasi-continuously and is ideally suited to explore the
angular dependence of TAMR using scanning tunneling microscopy (STM). We find
that the induced magnetic moments of Pb and Bi adatoms and dimers are small,
however, the spin-polarization of the local density of states (LDOS) is still
very large. The TAMR obtained from the anisotropy of the vacuum LDOS is up to
50-60 % for adatoms. For dimers the TAMR depends sensitively on the dimer
orientation with respect to the crystallographic directions of the surface due
to the formation of bonds between the adatoms with the Mn surface atoms and the
symmetry of the spin-orbit coupling induced mixing. Dimers oriented along the
spin spiral direction of the Mn monolayer display the largest TAMR of 60 %
which is due to hybrid 6p-3d states of the dimers and the Mn layer

Materials Science;Mesoscale and Nanoscale Physics