Temperature dependence of anisotropic magnetoresistance in antiferromagnetic Sr2IrO4

Abstract

We report point-contact measurements of anisotropic magnetoresistance (AMR) in a single crystal of antiferromagnetic (AFM) Mott insulator Sr2IrO4. The point-contact technique is used here as a local probe of magnetotransport properties on the nanoscale. The measurements at liquid nitrogen temperature revealed negative magnetoresistances (MRs) (up to 28%) for modest magnetic fields (250 mT) applied within the IrO2 a-b plane and electric currents flowing perpendicular to the plane. The angular dependence of MR shows a crossover from four-fold to two-fold symmetry in response to an increasing magnetic field with angular variations in resistance from 1-14%. We tentatively attribute the four-fold symmetry to the crystalline component of AMR and the field-induced transition to the effects of applied field on the canting of AFM-coupled moments in Sr2IrO4. The observed AMR is very large compared to the crystalline AMRs in 3d transition metal alloys/oxides (0.1-0.5%) and can be associated with the large spin-orbit interactions in this 5d oxide while the transition provides evidence of correlations between electronic transport, magnetic order and orbital states. The finding of this work opens an entirely new avenue to not only gain a new insight into physics associated with spin-orbit coupling but also better harness the power of spintronics in a more technically favorable fashion.

Electrically tunable transport in the antiferromagnetic Mott insulatorSr2IrO4

“…5a gives a band-gap change of about 0.34 meV. Furthermore, the switching threshold I c exhibits a clear magnetic field dependence I c (μ 0 H), which correlates with the point-contact R(μ 0 H) magnetoresistance [13] observed at zero bias (compare Figs. 5b and 5c).…”

“…The increase in I c (μ 0 H) with increasing field correlates with the decrease in R(μ 0 H), but their relative changes are quite different and cannot be explained by a field-independent critical voltage V c =I c R. Previous studies suggested that lattice distortions in SIO may cause a magnetoresistive effect due to a strong spin-orbit coupling [7,8,13] . The correlations between the magnetoresistance and resistive switching observed in our present work suggest that the magnetoresistive phenomenon in SIO could originate from the band structure modifications associated with the field-induced lattice distortions.The interplay between magnetism and electron transport may be further illustrated by studying the effects of bias on SIO magnetoresistance (MR) [13] . The MR was previously [13] associated with a crystalline component of anisotropic magnetoresistance (AMR) and the effects of applied field on the canting of antiferromagnetically coupled moments in SIO.…”

“…5b and 5c). The increase in I c (μ 0 H) with increasing field correlates with the decrease in R(μ 0 H), but their relative changes are quite different and cannot be explained by a field-independent critical voltage V c =I c R. Previous studies suggested that lattice distortions in SIO may cause a magnetoresistive effect due to a strong spin-orbit coupling [7,8,13] . The correlations between the magnetoresistance and resistive switching observed in our present work suggest that the magnetoresistive phenomenon in SIO could originate from the band structure modifications associated with the field-induced lattice distortions.…”

“…Figure 1a shows current-voltage (I-V) characteristics of 10 different point-contacts with zero-bias resistances ranging from 13 kΩ to 27 kΩ measured at T = 77 K. Contact sizes a can be estimated from the measured contact resistance R using a simple model [12] for diffusive transport that gives R=ρ/2a, where ρ is the resistivity of SIO. Assuming ρ  50 cm at liquid nitrogen temperature [7] , this analysis yields a ranging from 4.8 μm -2.3 μm for R = 13 kΩ -27 kΩ [13] . The local electric fields and current densities at the highest bias are of the order E ~ 10 7 V/m and j ~ 10 8 A/m 2 , respectively.…”

“…The interplay between magnetism and electron transport may be further illustrated by studying the effects of bias on SIO magnetoresistance (MR) [13] . The MR was previously [13] associated with a crystalline component of anisotropic magnetoresistance (AMR) and the effects of applied field on the canting of antiferromagnetically coupled moments in SIO.…”