Prediction of a Giant Tunneling Magnetoresistance Effect in Antiferromagnetic Tunnel Junctions
Evgeny Tsymbal, University of Nebraska-Lincoln
July 15th, 2022
Antiferromagnetic (AFM) spintronics has emerged as a subfield of spintronics , where the Néel vector is exploited to control spin-dependent transport properties. Due to being robust against magnetic perturbations, producing no stray fields, and exhibiting ultrafast dynamics, antiferromagnets can serve as promising functional materials for spintronic applications.
Here, we predict the critical functionality of antiferromagnets, namely their ability to produce a strong electrical response to the state of the Néel vector. This functionality is achieved using AFM metals with magnetic space group symmetry supporting a non-spin-degenerate Fermi surface. Due to their momentum-dependent spin polarization, such antiferromagnets can be used as electrodes in AFM tunnel junctions (AFMTJs) to control spin-dependent tunneling. In the transport regime conserving electron’s spin and transverse momentum, AFMTJ conductance is largely controlled by the spin matching of the conduction channels of the two electrodes. If their relative momentum-dependent spin polarization changes in response to the Néel vector direction, the net conductance of the AFMTJ alters, thus producing a tunneling magnetoresistance (TMR) effect.
We demonstrate this functionality for two types of AFMTJs based on different kinds of AFM electrodes: collinear RuO2 and non-collinear Mn3Sn. For the former , we design an all-oxide RuO2/TiO2/RuO2 (001) AFMTJ where an excellent match of RuO2 and TiO2 lattices allows epitaxial growth of the heterostructure maintaining its monocrystallinity. Using quantum-mechanical transport calculations, we predict a TMR effect as large as ~500%. For the latter , we consider an AFMTJ based on Mn3Sn (001) electrodes assuming for simplicity a vacuum barrier. We predict a TMR effect of ~300% with the junction resistance exhibiting four non-volatile resistance states dependent on the relative orientation of the Néel vector. The predicted effects are comparable to TMR in well-known magnetic tunnel junctions (MTJs) based on an MgO barrier layer, thus demonstrating the efficiency of AFMTJs to detect the Néel vector state.
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 J. Dong, X. Li, G. Gurung, M. Zhu, P. Zhang, F. Zheng, E. Y. Tsymbal, and J. Zhang, Tunneling magnetoresistance in noncollinear antiferromagnetic tunnel junctions. Physical Review Letters 128, 197201 (2022).