Matthias Althammer: Pure Spin Currents in Compensated Rare Earth Iron Garnets

Pure spin currents, i.e. the net flow of spin angular momentum without an accompanying charge current, represent a new paradigm for spin transport and spintronics. We have experimentally studied two novel magnetoresistance effects, which arise from the interaction of charge and spin current flows in ferromagnetic insulator/normal metal hybrid structures.

In a first series of experiments, we measured the resistance of gadolinium iron garnet (GdIG)/Pt hybrid structures as a function of the magnitude and the orientation of an external magnetic field. The spin Hall magnetoresistance (SMR) [1,2] in these samples exhibits a sign change at the magnetization compensation temperature of GdIG. We show that this sign change is related to the spin-canting of the magnetic sublattices of GdIG at these temperatures, which highlight the versatility of SMR experiments.

In a second series of experiments, we study the local and non-local magnetoresistance of thin Pt strips deposited onto yttrium iron garnet [3]. We compare the local magnetoresistance response of a Pt strip under current bias and the non-local voltage drop along a second, electrically isolated Pt strip, which is separated from the current carrying one by a few 100 nm. The non-local magnetoresistance exhibits the symmetry expected for a magnon spin accumulation-driven process [4]. Our experiments as a function of temperature and applied field orientation show that the magnon mediated magnetoresistance (MMR) is qualitatively different from the SMR. Especially, the MMR vanishes at temperatures below 10 K while the SMR prevails even at low temperatures. In addition, we studied the MMR response and temperature dependence of GdIG/Pt heterostructures and compare it to the results obtained for YIG/Pt devices.