Solution‐processed lead halide perovskites (LHPs) hold great promise for low‐cost high‐performance solar cells and light‐emitting devices, but they also suffer from a serious operating instability problem due to the ionic migration and lattice decomposition driven by strong electric fields. Here, considerably suppressed ionic migration and enhanced lattice stability in LHPs with partial substitution of Pb with 3d transition metal (TM: Mn and Ni) are reported. It is experimentally shown that the energy barrier for ionic migration in CsPbBr3 can be increased fourfold by Mn and Ni substitution, even with a small doping level (<4%). However, post‐TM Zn and non‐TM Bi incorporations are less efficient in suppressing ionic migration. The theoretical results reveal that Ni and Mn ions with partially filled 3d orbitals can passivate the active lone‐pair electron of surrounding Pb‐Br octahedrons via a coordination effect and reduce the Pb 6s‐Br 4p antibonding states, resulting in long‐range lattice stabilization and suppressed ionic migration. The Ni incorporation strategy in mixed‐halogen CsPbBr1.5I1.5 is further demonstrated, for which the field‐driven halogen segregation is significantly mitigated and the associated emission color variation is reduced sixfold. This study paves the way for improving the operating stability in LHP‐based optoelectronic and electronic devices.
We investigated the spin–orbit torque (SOT) and unidirectional spin Hall magnetoresistance (USMR) in Pt/CoFe/Ta trilayer as well as Pt/CoFe and CoFe/Ta bilayers with in-plane magnetic anisotropy by performing transverse and longitudinal second harmonic resistance measurements. Compared to the two bilayers, we found that the trilayer exhibits enhanced SOT and USMR due to the opposite spin Hall angles of Pt and Ta, which work together to enhance the spin accumulation in the trilayer. Furthermore, we found that thermal annealing has a significant influence on the magnitude and sign of the SOT and USMR in the Pt/CoFe/Ta trilayers. Specifically, we observed that both the damping-like SOT and USMR of the trilayer decrease as the annealing temperature increases, and they even change signs at an annealing temperature between 235 and 265 °C. In contrast, the sign change of the SOT and USMR upon annealing is absent in the Pt/CoFe and CoFe/Ta bilayers. These findings suggest that the sign of the SOT and USMR in the Pt/CoFe/Ta trilayer can be easily manipulated by using an appropriate thermal annealing treatment, which has important implications for the development of novel spintronic devices.
We report that the efficiency of the spin-Hall spin–orbit torque (SOT) in perpendicularly magnetized Pt/Co/MgO films can be engineered by introducing ruthenium (Ru) impurities into the bulk of the Co layer. As the concentration of the Ru impurities increases, the effective field of the damping-like SOT is increased by a factor of 2.3, leading to SOT efficiency per unit current density enhancing from 0.069 to 0.155. However, the Ru incorporation shows less impact on the field-like SOT efficiency. First-principles calculations reveal that the Ru incorporation can significantly increase the density of states of the majority spin at the Fermi level but has less influence on the minority spin case. We suspect that such an electronic-structure modulation may reduce the scattering of the spin-Hall spin currents flowing across the Co-Ru layer, resulting in SOT efficiency enhancement. The SOT enhancement by Ru incorporation is also observed in Ta/CoFeB/MgO films, indicating that modulating the spin scattering inside ferromagnets with judiciously selected impurities is a promising strategy to construct low-power-dissipation SOT spintronic devices.
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