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We experimentally investigate and quantitatively analyze the spin Hall magnetoresistance effect in ferromagnetic insulator/platinum and ferromagnetic insulator/nonferromagnetic metal/platinum hybrid structures. For the ferromagnetic insulator, we use either yttrium iron garnet, nickel ferrite, or magnetite and for the nonferromagnet, copper or gold. The spin Hall magnetoresistance effect is theoretically ascribed to the combined action of spin Hall and inverse spin Hall effect in the platinum metal top layer. It therefore should characteristically depend upon the orientation of the magnetization in the adjacent ferromagnet and prevail even if an additional, nonferromagnetic metal layer is inserted between Pt and the ferromagnet. Our experimental data corroborate these theoretical conjectures. Using the spin Hall magnetoresistance theory to analyze our data, we extract the spin Hall angle and the spin diffusion length in platinum. For a spin-mixing conductance of 4 × 10 14 −1 m −2 , we obtain a spin Hall angle of 0.11 ± 0.08 and a spin diffusion length of (1.5 ± 0.5) nm for Pt in our thin-film samples.

We describe the results of electronic Raman-scattering experiments in differently doped single crystals of YBa 2 Cu 3 O 6ϩx and Bi 2 Sr 2 (Ca x Y 1Ϫx )Cu 2 O 8 . The data in antiferromagnetic insulating samples suggest that at least the low-energy parts of the spectra of metallic samples originate predominantly from excitations of free carriers. We therefore propose an analysis of the data in terms of a memory function approach which has been introduced earlier for the current response. Dynamical scattering rates ⌫()ϭ1/() and mass-enhancement factors 1ϩ()ϭm*()/m of the carriers are obtained. It is found that a strong polarization dependence of the carrier lifetime develops towards low doping. In B 2g (xy) symmetry selecting predominantly electrons with momenta along the diagonals of the CuO 2 planes the Raman data compare well with the results obtained from dc and dynamical transport. In B 1g (x 2 Ϫy 2 ) symmetry projecting out momenta along the Cu-O bonds the dc scattering rates of underdoped materials become temperature independent and considerably larger than in B 2g symmetry. This increasing anisotropy is accompanied by a loss of spectral weight in B 2g symmetry in the range between the superconducting transition at T c and a characteristic temperature T* of the order of room temperature which compares well with the pseudogap temperature found in other experiments. The energy range affected by the pseudogap is doping and temperature independent. The integrated spectral loss is approximately 25% in underdoped samples and becomes much weaker towards higher carrier concentration. In underdoped samples, superconductivity-related features in the spectra can be observed only in B 2g symmetry. The peak frequencies scale with T c . We do not find a direct relation between the pseudogap and the superconducting gap.

A scannable laser beam is used to generate local thermal gradients in metallic (Co2FeAl) or insulating (Y3Fe5O12) ferromagnetic thin films. We study the resulting local charge and spin currents that arise due to the anomalous Nernst effect (ANE) and the spin Seebeck effect (SSE), respectively. In the local ANE experiments, we detect the voltage in the Co2FeAl thin film plane as a function of the laser-spot position and external magnetic field magnitude and orientation. The local SSE effect is detected in a similar fashion by exploiting the inverse spin Hall effect in a Pt layer deposited on top of the Y3Fe5O12. Our findings establish local thermal spin and charge current generation as well as spin caloritronic domain imaging.

We investigate the spin Hall magnetoresistance in thin film bilayer heterostructures of the heavy metal Pt and the antiferromagnetic insulator NiO. While rotating an external magnetic field in the easy plane of NiO, we record the longitudinal and the transverse resistivity of the Pt layer and observe an amplitude modulation consistent with the spin Hall magnetoresistance. In comparison to Pt on collinear ferrimagnets, the modulation is phase shifted by 90 • and its amplitude strongly increases with the magnitude of the magnetic field. We explain the observed magnetic field-dependence of the spin Hall magnetoresistance in a comprehensive model taking into account magnetic field induced modifications of the domain structure in antiferromagnets. With this generic model we are further able to estimate the strength of the magnetoelastic coupling in antiferromagnets. Our detailed study shows that the spin Hall magnetoresistance is a versatile tool to investigate the magnetic spin structure as well as magnetoelastic effects, even in antiferromagnetic multi-domain materials. J c J s σ large ρ J c J s σ FMI HM FMI HM (a) (b) j t n J s stt J s back J c J c J s σ AFI HM AFI HM J s stt J s back FMI/HM bilayer AFI/HM bilayer m m * stephan.gepraegs@wmi.badw.de