Evidence of orbital Hall current-induced correlation in second-harmonic response of longitudinal and transverse voltage in light metal–ferromagnet bilayers

We investigate the effect of orbital current arising from orbital Hall effect in thin films of light metals of Nb and Ti in Ohmic contact with ferromagnetic Ni in the second-harmonic longitudinal and transverse voltages, in response to an a.c. current applied to the bilayer structures. Analogous to the experiments on heavy metal–ferromagnet bilayers, we extract the orbital Hall torque efficiency and unidirectional orbital magnetoresistance (UOMR) per unit current density. Control experiments on light metal bilayers with NiFe (permalloy) as ferromagnet and a single layer of Ni show absence of torque and suppression of UOMR, corroborating the role of Ni as an efficient converter of orbital to spin current and role of light metals as source of orbital current. We find that both orbital Hall torque efficiency and unidirectional orbital magnetoresistance are proportionately higher in Ti as compared to Nb, confirming a correlation between the two effects arising from the same orbital current in the respective light metals.