Anisotropic Magnetoresistance in AntiferromagneticSr2IrO4

We report point-contact measurements of anisotropic magnetoresistance (AMR)\nin a single crystal of antiferromagnetic (AFM) Mott insulator Sr2IrO4. The\npoint-contact technique is used here as a local probe of magnetotransport\nproperties on the nanoscale. The measurements at liquid nitrogen temperature\nrevealed negative magnetoresistances (MRs) (up to 28%) for modest magnetic\nfields (250 mT) applied within the IrO2 a-b plane and electric currents flowing\nperpendicular to the plane. The angular dependence of MR shows a crossover from\nfour-fold to two-fold symmetry in response to an increasing magnetic field with\nangular variations in resistance from 1-14%. We tentatively attribute the\nfour-fold symmetry to the crystalline component of AMR and the field-induced\ntransition to the effects of applied field on the canting of AFM-coupled\nmoments in Sr2IrO4. The observed AMR is very large compared to the crystalline\nAMRs in 3d transition metal alloys/oxides (0.1-0.5%) and can be associated with\nthe large spin-orbit interactions in this 5d oxide while the transition\nprovides evidence of correlations between electronic transport, magnetic order\nand orbital states. The finding of this work opens an entirely new avenue to\nnot only gain a new insight into physics associated with spin-orbit coupling\nbut also better harness the power of spintronics in a more technically\nfavorable fashion.\n