Junction using collinear nickel oxide insulator produces spin-polarized current

Antiferromagnetic materials have shown promise for use in spintronic applications because they are robust against perturbation of magnetic fields, produce no stray fields, and display ultrafast dynamics. Generating and manipulating spin-polarized current in such materials, however, remains difficult because of the symmetry of spin sublattices. Using nickel oxide may help to overcome this constraint.

Tong et al. have constructed a prototype junction composed of a gold-nickel oxide-gold junction in which a collinear nickel oxide insulator can break spin sublattice symmetry using an external bias voltage. Such a system demonstrates the appearance of spin-polarized current by inducing a nonequivalent transport for spin-up and spin-down currents.

“It has long been believed that spin-polarized current could not be achieved in collinear antiferromagnetic materials because of the symmetry of spin sublattices,” said author Xianmin Zhang. “Here, we show the symmetry of antiferromagnetic spin sublattices could be broken by the bias voltage and then induced the spin-polarized currents in collinear antiferromagnetic materials.”

The work provides a path forward for ameliorating the large resistance mismatch that prevents very small spin injection from metallic electrodes into semiconductors, which would allow for easier combining of spintronics and semiconductor electronics.

In addition to adjusting the magnitude, the group was able to modify the sign of the spin polarization by varying the bias. The system obtains a positive spin polarization up to 80 percent at roughly 0.9 volts and the negative one appears beyond a bias voltage of 1.6 volts.

Zhang hopes the findings help pave the way for development of novel antiferromagnetic spintronic devices and looks to continue exploring the manipulation of such materials.

Source: “High and reversible spin polarization in a collinear antiferromagnet,” by Junwei Tong, Feifei Luo, Liuxia Ruan, Gaowu Qin, Lianqun Zhou, Fubo Tian, and Xianmin Zhang, Applied Physics Reviews (2020). The article can be accessed at https://doi.org/10.1063/5.0004564 .