Strong spin orientation-dependent spin current diffusion and inverse spin Hall effect in a ferromagnetic metal

Pure spin current transport has become the central point of the state-of-the-art spintronics. While most spin current phenomena have been extensively explored, aspects of the pure spin current injected into ferromagnetic metals are far from completely understood. The reports on a fundamental problem, i.e. the spin relaxation asymmetry with spin current polarization collinear or transverse to the magnetization of ferromagnetic metals, are quite controversial. By employing a Y3Fe5O12 (YIG)/Cu/Ni80Fe20 (Py)/Ir25Mn75 (IrMn) spin valve heterostructure with the thermal inverse spin Hall effect (ISHE) of a Py well separated from other thermoelectric transport and thermal Hall effects, we find that the ISHE signal amplitude in 10 nm Py increases by 80% when changing the relative orientation of the YIG and Py magnetization from orthogonal (perpendicular to) to collinear (||). Moreover, the spin-diffusion length lambda(sf) and effective spin Hall angle theta SHeff of Py are also spin orientation dependent and vary from lambda sf perpendicular to = 1.0 +/- 0.1 nm to lambda sf parallel to = 2.8 +/- 0.5 nm with theta SHeff parallel to = 1.5, respectively. Our results demonstrate magnetization orientation-dependent spin relaxation and spin injection efficiency of a pure spin current, revealing that exchange interactions in ferromagnetic metals strongly affect the transport of the pure spin current.