Anisotropic magnetoresistance in an antiferromagnetic semiconductor

Abstract

Recent studies in devices comprising metal antiferromagnets have demonstrated the feasibility of a novel spintronic concept in which spin-dependent phenomena are governed by an antiferromagnet instead of a ferromagnet. Here we report experimental observation of the anisotropic magnetoresistance in an antiferromagnetic semiconductor Sr 2 IrO 4 . Based on ab initio calculations, we associate the origin of the phenomenon with large anisotropies in the relativistic electronic structure. The antiferromagnet film is exchange coupled to a ferromagnet, which allows us to reorient the antiferromagnet spin-axis in applied magnetic fields via the exchange spring effect. We demonstrate that the semiconducting nature of our AFM electrode allows us to perform anisotropic magnetoresistance measurements in the currentperpendicular-to-plane geometry without introducing a tunnel barrier into the stack. Temperature-dependent measurements of the resistance and anisotropic magnetoresistance highlight the large, entangled tunabilities of the ordinary charge and spin-dependent transport in a spintronic device utilizing the antiferromagnet semiconductor.

Anisotropic Magnetoresistance in AntiferromagneticSr2IrO4

“…1(a)-correlate very well with this transition and previously observed MRs in bulk Sr 2 IrO 4 samples [15]. We, thus, attribute the observed variations in RðHÞ to the field-induced variations in the magnetic order of Sr 2 IrO 4 while the observed angular variations in RðθÞ can be attributed to the crystalline AMR [6]. The latter is further confirmed by correlations between the observed symmetry of AMR and the crystal structure, as we discuss next.…”

“…This spin-orbit coupling induced effect arises from the crystal symmetries and reflects the effects of orbital degrees of freedom on the magnetoelectronic transport in Sr 2 IrO 4 . Note that the AMR observed in our point contacts can be as large as 14%, which is very large when compared to the crystalline AMRs reported previously in 3d transition metal alloys or oxides (0.1%-0.5%) [21][22][23] and is also much larger than the crystalline AMRs observed to date in Sr 2 IrO 4 [6].…”

“…As AMR is known to be closely associated with spin-orbit interaction, the strong spin-orbit interaction in this 5d transition metal oxide may favor stronger AMR compared to 3d transition metal alloys and oxides. The recent magnetotransport studies in Sr 2 IrO 4 single crystals [14,15] and thin films [6] revealed largely unexplored correlations between electronic transport, magnetic order, and orbital states.Here, we present the first observation of the pointcontact AMR in single crystals of the AFM Mott insulator Sr 2 IrO 4 [14-16], which can potentially be used to sense the AFM order parameter in spintronic nanodevices. The pointcontact technique allows us to probe very small volumes and, therefore, measures electronic transport on a microscopic scale.…”

“…As AMR is known to be closely associated with spin-orbit interaction, the strong spin-orbit interaction in this 5d transition metal oxide may favor stronger AMR compared to 3d transition metal alloys and oxides. The recent magnetotransport studies in Sr 2 IrO 4 single crystals [14,15] and thin films [6] revealed largely unexplored correlations between electronic transport, magnetic order, and orbital states.…”

“…One of the milestones of AFM spintronics is finding an efficient method for monitoring the magneticorder parameter in AFM materials. Anisotropic magnetoresistance (AMR) [6] and tunneling AMR [7,8] observed in AFMs are among very promising candidates for this purpose. The canted AFM iridate Sr 2 IrO 4 (see Fig.…”