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 (⊥) to collinear (||). Moreover, the spin-diffusion length λsf and effective spin Hall angle $$\theta _{{\mathrm{SH}}}^{{\mathrm{eff}}}$$ of Py are also spin orientation dependent and vary from $$\lambda _{{\mathrm{sf}}}^ \bot$$ = 1.0 ± 0.1 nm to $$\lambda _{{\mathrm{sf}}}^\parallel$$ = 2.8 ± 0.5 nm with $$\theta _{{\mathrm{SH}}}^{{\mathrm{eff}}}\left( \bot \right)/\theta _{{\mathrm{SH}}}^{{\mathrm{eff}}}\left( \parallel \right)$$ = 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. A method for converting quantum spin properties into electricity can be enhanced using magnetic fields. Jian-Wang Cai from the Chinese Academy of Sciences in Beijing, China and colleagues investigated how insulating magnets can transmit information via a phenomenon known as spin current generation. When heat is applied to nanoscale nickel–iron films, information about the magnet’s spin orientation moves through the alloy much like a wave through water. Placing an antiferromagnetic metal on top of the nickel–iron film enables the spin current to be captured and converted into electricity without any spurious effect. The authors’ experiments showed that spin currents could be boosted or diminished by applying external magnetic fields parallel or across the device. Analysis of this orientation dependence revealed how spin movement across interfaces may affect this new type of power generation. The authors demonstrate that the inverse spin Hall effect (ISHE) and pure spin current relaxation in Ni80Fe20 (Py) are strong magnetization orientation dependent through longitudinal spin-Seebeck effect measurement in YIG/Cu/Py/Ir25Mn75 spin valve heterostructure. With the relative orientation of the magnetization of YIG and Py varying from perpendicular (⊥) to collinear (||), it has been found that the detected ISHE amplitude in 10 nm Py increases by 80%. Besides, the spin-diffusion length λsf varies from $$\lambda _{{\mathrm{sf}}}^ \bot$$ = 1.0 ± 0.1 nm to $$\lambda _{{\mathrm{sf}}}^\parallel$$ = 2.8 ± 0.5 nm and the effective spin Hall angle $$\theta _{{\mathrm{SH}}}^{{\mathrm{eff}}}\left( \bot \right)/\theta _{{\mathrm{SH}}}^{{\mathrm{eff}}}\left( \parallel \right) = 1.5$$.