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For the spin-to-charge conversion (SCC) in heavy metal/ferromagnet (HM/FM) heterostructure, the contribution of interfacial spin-orbit coupling (SOC) remains controversial. Here, we investigate the SCC process of the Pt/NiFe heterostructure by the spin pumping in YIG/Pt/NiFe/IrMn multilayers. Due to the exchange bias of NiFe/IrMn structure, the NiFe magnetization can be switched between magnetically unsaturated and saturated states by opposite resonance fields of YIG layer. The spin-pumping signal is found to decrease significantly when the NiFe magnetization is changed from the saturated state to the unsaturated state. Theoretical analysis indicates that the interfacial spin absorption is enhanced for the above-mentioned NiFe magnetic state change, which results in the increased and decreased spin flow in the Pt layer and across the Pt/NiFe interface, respectively. These results demonstrate that in our case the interfacial SOC effect at the Pt/NiFe interface is dominant over the bulk inverse spin Hall effect in the Pt layer. Our work reveals a significant role of interfacial SOC in the SCC in HM/FM heterostructure, which can promote the development of high-efficiency spintronic devices through interfacial engineering.

Thanks to the strong perpendicular magnetic anisotropy (PMA), excellent processing compatibility as well as novel spintronic phenomenon, Co/Pt multilayers have been attracting massive attention and widely used in magnetic storage. However, reversed magnetic domains come into being with the increasing layer repetition ‘N’ to reduce magneto-static energy, resulting in the remarkable diminishment of the remanent magnetization (M r). As a result, the product of M r and thickness (i.e., the remanent moment-thickness product, M r t), a key parameter in magnetic recording for reliable data storing and reading, also decreases dramatically. To overcome this issue, we deposit an ultra-thick granular [Co/Pt]80 multilayer with a total thickness of 68 nm on granular SiN x buffer layer. The M r t value, M r to saturation magnetization (M s) ratio as well as out of plane (OOP) coercivity (H coop) are high up to 2.97 memu/cm2, 67%, and 1940 Oe (1 Oe = 79.5775 A⋅m−1), respectively, which is remarkably improved compared with that of continuous [Co/Pt]80 multilayers. That is because large amounts of grain boundaries in the granular multilayers can efficiently impede the propagation and expansion of reversed magnetic domains, which is verified by experimental investigations and micromagnetic simulation results. The simulation results also indicate that the value of M r t, M r/M s ratio, and H coop can be further improved through optimizing the granule size, which can be experimentally realized by manipulating the process parameter of SiN x buffer layer. This work provides an alternative solution for achieving high M r t value in ultra-thick Co/Pt multilayers, which is of unneglectable potential in applications of high-density magnetic recording.

Antiferromagnetic insulators have recently been proved to support spin current efficiently. Here, we report the damping-like spin- orbit torque (SOT) in Pt / NiO / CoFeB has a strong temperature dependence and reverses the sign below certain temperatures, which is different from the slight variation with temperature in the Pt / CoFeB bilayer. The negative damping-like SOT at low temperatures is proposed to be mediated by the magnetic interactions that tie with the “exchange bias” in Pt / NiO / CoFeB, in contrast to the thermal-magnon-mediated scenario at high temperatures. Our results highlight the promise to control the SOT through tuning the magnetic structure in multilayers.

The exchange bias field (Hex) and tunneling magnetoresistance (TMR) ratio play an important role for the applications of magnetic tunnel junction (MTJ) in spintronic devices. Here the structure, magnetic properties, and TMR ratio are systematically investigated for the IrMn-based MTJ (IrMn/CoFe/Ru/CoFe/CoFeB/MgO/CoFeB) with seed layers of Ta, Ta/Ru, NiFeCr and Ta/NiFe. The MTJs with seed layers of Ta/Ru and Ta/NiFe present high Hex values, and the MTJ with seed layer of Ta/Ru shows the highest TMR ratio. We found that the Hex is positively correlated with the (111) texture quality of the IrMn layer while the interdiffusion at the interfaces of CoFeB/MgO/CoFeB has significant impact on the TMR ratio. These results highlight the crucial role of seed layers on the Hex and TMR ratio, and suggest that the Ta/Ru seed layer is beneficial to developing MTJ-based spintronic devices such as magnetic field sensor towards high sensitivity and high stability.

Effective probing current-induced magnetization switching is highly required in the study of emerging spin–orbit torque (SOT) effect. However, the measurement of in-plane magnetization switching typically relies on the giant/tunneling magnetoresistance measurement in a spin valve structure calling for complicated fabrication process, or the non-electric approach of Kerr imaging technique. Here, we present a reliable and convenient method to electrically probe the SOT-induced in-plane magnetization switching in a simple Hall bar device through analyzing the MR signal modified by a magnetic field. In this case, the symmetry of MR is broken, resulting in a resistance difference for opposite magnetization orientations. Moreover, the feasibility of our method is widely evidenced in heavy metal/ferromagnet (Pt/Ni20Fe80and W/Co20Fe60B20) and the topological insulator/ferromagnet (Bi2Se3/Ni20Fe80). Our work simplifies the characterization process of the in-plane magnetization switching, which can promote the development of SOT-based devices.