67 research outputs found
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
, with the Fermi temperature and the Curie
temperature . Since, typically, , 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
Giant Magnetothermal Conductivity Switching in Semimetallic WSi Single Crystals
Materials able to rapidly switch between thermally conductive states by
external stimuli such as electric or magnetic fields can be used as
all-solid-state thermal switches and open a myriad of applications in heat
management, power generation and cooling. Here, we show that the large
magnetoresistance that occurs in the highly conducting semimetal
-WSi single crystals leads to dramatically large changes in
thermal conductivity at temperatures <100 K. At temperatures <20 K, where
electron-phonon scattering is minimized, the thermal conductivity switching
ratio between zero field and a 9T applied field can be >7. We extract the
electronic and lattice components of the from the thermal conductivity
measurements and show that the Lorenz number for this material approximates the
theoretical value of L. From the heat capacity and thermal diffusivity,
the speed of thermal conductivity switching is estimated to range from 1 x
10 seconds at 5 K to 0.2 seconds at 100 K for a 5-mm long sample. This
work shows that WSi, a highly conducting multi-carrier semimetal, is a
promising thermal switch component for low-temperature applications such
cyclical adiabatic demagnetization cooling, a technique that would enable
replacing He-based refrigerators.Comment: 20 pages, 6 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
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