RESUMEN
The quantum anomalous Hall (QAH) effect is characterized by a dissipationless chiral edge state with a quantized Hall resistance at zero magnetic field. Manipulating the QAH state is of great importance in both the understanding of topological quantum physics and the implementation of dissipationless electronics. Here, the QAH effect is realized in the magnetic topological insulator Cr-doped (Bi,Sb)2 Te3 (CBST) grown on an uncompensated antiferromagnetic insulator Al-doped Cr2 O3 . Through polarized neutron reflectometry (PNR), a strong exchange coupling is found between CBST and Al-Cr2 O3 surface spins fixing interfacial magnetic moments perpendicular to the film plane. The interfacial coupling results in an exchange-biased QAH effect. This study further demonstrates that the magnitude and sign of the exchange bias can be effectively controlled using a field training process to set the magnetization of the Al-Cr2 O3 layer. It demonstrates the use of the exchange bias effect to effectively manipulate the QAH state, opening new possibilities in QAH-based spintronics.
RESUMEN
Parasitic magnetism plays an important role in magnetoelectric spin switching of antiferromagnetic oxides, but its mechanism has not been clearly investigated. Unlike the widely obtained surface boundary magnetization in magnetoelectric Cr2O3 antiferromagnet, we previously reported that Al doping could produce volume-dependent parasitic magnetism (Mpara) in Cr2O3 with the remaining magnetoelectric effect and antiferromagnetic properties. In this work, we systematically investigated the magnetic properties of Mpara in Cr2O3 through its different exchange coupling characteristics with the ferromagnet at various conditions. The columnar grain boundaries cause an antiferromagnetic sublattice breaking to produce uncompensated spins and thus are considered to be responsible for Mpara in both undoped and Al-doped Cr2O3. Finally, a model was proposed for the formation mechanism of the parasitic magnetism in Cr2O3, which explains the reported magnetic characteristics of Cr2O3, and some current topics such as the domain formation and motion in Cr2O3 during magnetoelectric spin switching. This work contributes to a deep understanding of antiferromagnetic spintronics and provides a method to realize the low-energy operation of antiferromagnetic-based magnetic random access memory.
RESUMEN
Nano-contact magnetoresistance (NCMR) spin-valves (SVs) using an AlO x nano-oxide-layer (NOL) have numerous nanocontacts in the thin AlOx oxide layer. The NCMR theoretically depends on the bulk scattering spin asymmetry ([Formula: see text]) of the ferromagnetic material in the nanocontacts. To determine the relationship between NCMR and [Formula: see text], we investigated the dependence of NCMR on the composition of the ferromagnetic material Co1-xFex. The samples were annealed at 270 °C and 380 °C to enhance the MR ratio. For both annealing temperatures, the magnetorsistance ratio in the low-resistance area product region at less than 1 Ω µm2 was maximized for Co0.5Fe0.5. To evaluate [Formula: see text] exactly, we fabricated current-perpendicular-to-plane giant magnetoresistance SVs with Co1-xFex/Cu/Co1-xFex layers and used Valet and Fert's theory to solve the diffusion equation of the spin accumulation for a ferromagnetic layer/non-ferromagnetic layer of five layers with a finite diffusion length. The evaluated [Formula: see text] for Co1-xFex was also maximized for Co0.5Fe0.5. Additionally, to determine the difference between the experimental MR ratio of NCMR SVs and the theoretical MR ratio, we fabricated Co0.5Fe0.5 with oxygen impurities and estimated the decrease in [Formula: see text] with increasing oxygen impurity concentration. Our Co0.5Fe0.5 nano-contacts fabricated using ion-assisted oxidation may contain oxygen impurities, and the oxygen impurities might cause a decrease in [Formula: see text] and the MR ratio.