The realization of fourfold anisotropic magnetoresistance (AMR) in $3d-5d$ heterostructures has boosted major efforts in antiferromagnetic (AFM) spintronics. However, despite the potential of incorporating strong spin-orbit coupling, only small AMR signals have been detected thus far, prompting a search for mechanisms to enhance the signal. In this paper, we demonstrate an extraordinarily elevated fourfold AMR of 70% realized in $\mathrm{CaMn}{\mathrm{O}}_3/\mathrm{CaIr}{\mathrm{O}}_3$ thin film superlattices. We find that the biaxial magnetic anisotropy and the spin-flop transition in a nearly Mott insulating phase form a potent combination, each contributing one order of magnitude to the total signal. Dynamics between these phenomena capture a subtle interaction of pseudospin coupling with the lattice and external magnetic field, an emergent phenomenon creating opportunities to harness its potential in AFM spintronics.

• Received 21 January 2021
• Revised 4 November 2021
• Accepted 15 December 2021

DOI:https://doi.org/10.1103/PhysRevB.105.L020402