Magnons versus electrons in thermal spin transport through metallic interfaces

We develop a theory for spin transport in magnetic metals that treats the contribution of magnons and electrons on equal footing. As an application we consider thermally-driven spin injection across an interface between a magnetic metal and a normal metal, i.e., the spin-dependent Seebeck effect. We show that the ratio between magnonic and electronic contribution scales as $\sqrt{T/T_C}T_F/T_C$, with the Fermi temperature $T_F$ and the Curie temperature $T_C$. Since, typically, $T_C \ll T_F$, the magnonic contribution may dominate the thermal spin injection, even though the interface is more transparent for electronic spin current.Comment: Contribution to the Special issue on Spincaloritronics in Journal of Physics D: Applied Physic

Phonon driven spin distribution due to the spin-Seebeck effect

Here we report on measurements of the spin-Seebeck effect of GaMnAs over an extended temperature range alongside the thermal conductivity, specific heat, magnetization, and thermoelectric power. The amplitude of the spin-Seebeck effect in GaMnAs scales with the thermal conductivity of the GaAs substrate and the phonon-drag contribution to the thermoelectric power of the GaMnAs, demonstrating that phonons drive the spin redistribution. A phenomenological model involving phonon-magnon drag explains the spatial and temperature dependence of the measured spin distribution.Comment: 12 pages, 3 figure

Magnon-drag thermopower and Nernst coefficient in Fe, Co, and Ni

Magnon-drag is shown to dominate the thermopower of elemental Fe from 2 to 80 K and of elemental Co from 150 to 600 K; it is also shown to contribute to the thermopower of elemental Ni from 50 to 500 K. Two theoretical models are presented for magnon-drag thermopower. One is a hydrodynamic theory based purely on non-relativistic, Galilean, spin-preserving electron-magnon scattering. The second is based on spin-motive forces, where the thermopower results from the electric current pumped by the dynamic magnetization associated with a magnon heat flux. In spite of their very different microscopic origins, the two give similar predictions for pure metals at low temperature, allowing us to semi-quantitatively explain the observed thermopower of elemental Fe and Co without adjustable parameters. We also find that magnon-drag may contribute to the thermopower of Ni. A spin-mixing model is presented that describes the magnon-drag contribution to the Anomalous Nernst Effect in Fe, again enabling a semi-quantitative match to the experimental data without fitting parameters. Our work suggests that particle non-conserving processes may play an important role in other types of drag phenomena, and also gives a predicative theory for improving metals as thermoelectric materials.Comment: main text plus 7 figures; accepted in PRB September 201

Cyclotron motion and magnetic focusing in semiconductor quantum wells with spin-orbit coupling

We investigate the ballistic motion of electrons in III-V semiconductor quantum wells with Rashba spin-orbit coupling in a perpendicular magnetic field. Taking into account the full quantum dynamics of the problem, we explore the modifications of classical cyclotron orbits due to spin-orbit interaction. As a result, for electron energies comparable with the cyclotron energy the dynamics are particularly rich and not adequately described by semiclassical approximations. Our study is complementary to previous semiclassical approaches concentrating on the regime of weaker fields.Comment: 14 pages, 8 figures included, version to appear in Phys. Rev.

Evolution of structural and electronic properties of highly mismatched InSb films

We have investigated the evolution of structural and electronic properties of highly mismatched InSb films, with thicknesses ranging from 0.1 to 1.5 μm. Atomic force microscopy, cross-sectional transmission electron microscopy, and high-resolution x-ray diffraction show that the 0.1 μm films are nearly fully relaxed and consist of partially coalesced islands, which apparently contain threading dislocations at their boundaries. As the film thickness increases beyond 0.2 μm, the island coalescence is complete and the residual strain is reduced. Although the epilayers have relaxed equally in the 〈110〉 in-plane directions, the epilayer rotation about an in-plane axis (epilayer tilt) is not equal in both 〈110〉 in-plane directions. Interestingly, the island-like surface features tend to be preferentially elongated along the axis of epilayer tilt. Furthermore, epilayer tilt which increases the substrate offcut (reverse tilt) is evident in the [110] direction. High-resolution transmission electron microscopy indicates that both pure-edge and 60° misfit dislocations contribute to the relaxation of strain. In addition, as the film thickness increases, the threading dislocation density decreases, while the corresponding room-temperature electron mobility increases. The other structural features, including the residual strain, and the surface and interface roughness, do not appear to impact the electron mobility in these InSb films. Together, these results suggest that free-carrier scattering from the threading dislocations is the primary room-temperature mobility-limiting mechanism in highly mismatched InSb films. Finally, we show quantitatively that free-carrier scattering from the lattice dilation associated with threading dislocations, rather than scattering from a depletion potential surrounding the dislocations, is the dominant factor limiting the electron mobility. © 2000 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70332/2/JAPIAU-88-11-6276-1.pd

Thermopower and thermal conductivity in the Weyl semimetal NbP

The Weyl semimetal NbP exhibits an extremely large magnetoresistance (MR) and an ultra-high mobility. The large MR originates from a combination of the nearly perfect compensation between electron- and hole-type charge carriers and the high mobility, which is relevant to the topological band structure. In this work we report on temperature- and field-dependent thermopower and thermal conductivity experiments on NbP. Additionally, we carried out complementary heat capacity, magnetization, and electrical resistivity measurements. We found a giant adiabatic magnetothermopower with a maximum of 800 $\mu$V/K at 50 K in a field of 9 T. Such large effects have been observed rarely in bulk materials. We suggest that the origin of this effect might be related to the high charge-carrier mobility. We further observe pronounced quantum oscillations in both thermal conductivity and thermopower. The obtained frequencies compare well with our heat capacity and magnetization data.Comment: 6 pages, 3 figure

ANTIBODIES OF THE IgA TYPE IN INTESTINAL PLASMA CELLS OF GERMFREE MICE AFTER ORAL OR PARENTERAL IMMUNIZATION WITH FERRITIN

In adult germfree C3H mice immunized with horse spleen ferritin, either subcutaneously or intraperitoneally, plasma cells containing specific antibodies were found in lymph nodes and spleen and, in smaller numbers, also in the lamina propria of the intestine. In extraintestinal sites, these antiferritin-containing plasma cells were mainly of the IgM class after a single stimulation, and of the IgG1 class after repeated stimulation. In the intestine, all the anti-ferritin-containing cells appeared to be of the IgA class. Circulating antibodies, after repeated stimulation, were for the major part IgG1 and IgG2. In germfree mice given ferritin in their drinking water, antiferritin-containing cells were abundant in the intestinal mucosa, much less numerous in the mesenteric lymph nodes, and extremely scarce in other lymphoid tissues. All these cells, whatever their location, appeared to belong exclusively to the IgA class. Similarly, all the circulating antibody in these animals was found to be IgA. These findings illustrate the role of the gut as a site of antibody synthesis, as well as its selective commitment to the production of antibodies of the IgA class