Role of the nonmagnetic underlayer in controlling the electronic structure of ferromagnet/nonmagnetic-metal heterostructures

Heterostructures comprising of ferromagnet and nonmagnetic metal (NM) interfaces capable of generating spin torque are crucial for next-generation ultrafast magnetic switching devices. Here we present the effect of change of NM underlayer with different spin-orbit coupling (SOC) strength on the spin-dependent electronic structure of quintessential heterostructures of CoFeB/NM. The results reveal deviations from the conventional expectation of the dependence on the strength of SOC of the NM layer. Dichroic photoemission measurements indicate that the spin polarization of the ferromagnetic CoFeB layer is higher with the weaker-SOC Cu underlayer than that with the stronger-SOC Ta, Pt, and W underlayers. The phase space of the unoccupied electronic states near the Fermi level is found more for the W underlayer system than that of the Cu and Ta underlayer systems.