Magnetic phenomena, spin-orbit effects, and Landauer conductance in Pt nanowire contacts: Density-functional theory calculations

Platinum monatomic nanowires were predicted to spontaneously develop magnetism, involving a sizable orbital moment via spin-orbit coupling, and a colossal magnetic anisotropy. We present here a fully-relativistic (spin-orbit coupling included) pseudopotential density functional calculation of electronic and magnetic properties, and of Landauer ballistic conductance of Pt model nanocontacts consisting of short nanowire segments suspended between Pt leads or tips, represented by bulk planes. Even if short, and despite the nonmagnetic Pt leads, the nanocontact is found to be locally magnetic with magnetization strictly parallel to its axis. Especially under strain, the energy barrier to flip the overall spin direction is predicted to be tens of meV high, and thus the corresponding blocking temperatures large, suggesting the validity of static Landauer ballistic electrical conductance calculations. We carry out such calculations to find that inclusion of spin-orbit coupling and of magnetism lowers the ballistic conductance by about 15 divided by 20% relative to the nonmagnetic case, yielding G similar to 2G(0) (G(0)=2e(2)/h), in good agreement with break junction results. The spin filtering properties of this highly unusual spontaneously magnetic nanocontact are also analyzed.