Nontrivial torque generation by orbital angular momentum injection in ferromagnetic-metal/ Cu/Al2 O3 trilayers

Efficient electrical generation of torque is desired to develop innovative magnetic nanodevices. The torque can be generated by charge to spin conversion of heavy-metal layers through their strong spin-orbit interaction followed by the injection of the converted spin into adjacent ferromagnetic layers. However heavy atomic elements indispensable for this torque generation scheme are often incompatible with device mass production processes. Here we demonstrate efficient torque generation without heavy elements in ferromagnetic metal/ Cu/Al2 O3 trilayers. Despite the absence of heavy elements, their effective spin Hall conductivity can be one order of magnitude larger than those of heavy-metal based multilayers. Properties of the measured torque deviate from those of the spin-injection induced torque and are consistent instead with a recently proposed torque mechanism based on orbital angular momentum injection. Our results demonstrate a direction for magnetic nanodevices based on the orbital angular momentum injection.