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The interface between a ferro- or ferrimagnetic insulator and a normal metal can support spin currents polarized collinear with and perpendicular to the magnetization direction. The flow of angular momentum perpendicular to the magnetization direction (“transverse” spin current) takes place via spin torque and spin pumping. The flow of angular momentum collinear with the magnetization (“longitudinal” spin current) requires the excitation of magnons. In this article we extend the existing theory of longitudinal spin transport [Bender and Tserkovnyak, Phys. Rev. B 91, 140402(R) (2015)] in the zero-frequency weak-coupling limit in two directions: We calculate the longitudinal spin conductance nonperturbatively (but in the low-frequency limit) and at finite frequency (but in the limit of low interface transparency). For the paradigmatic spintronic material system YIG|Pt, we find that nonperturbative effects lead to a longitudinal spin conductance that is ca. 40% smaller than the perturbative limit, whereas finite-frequency corrections are relevant at low temperatures ≲100K only, when only few magnon modes are thermally occupied.

The discovery that the near-field radiative heat transfer enables to overcome the limit set by Planck’s law holds the promise to have an impact in different nanotechnologies that make use of thermal radiation, and the challenge now is to find strategies to actively control and manipulate this near-field thermal radiation. Here, we predict a huge anisotropic thermal magnetoresistance (ATMR) in the near-field radiative heat transfer between magneto-optical particles when the direction of an external magnetic field is changed with respect to the heat current direction. We illustrate this effect with the case of two InSb particles where we find that the ATMR amplitude can reach values of up to 800% for a magnetic field of 5 T, which is many orders of magnitude larger than its spintronic analogue. This thermomagnetic effect could find broad applications in the field of ultrafast thermal management as well as magnetic and thermal remote sensing., We acknowledge funding from the Spanish MINECO (FIS2014-53488-P, FIS2017-84057-P and MAT2014-58860-P) and the Comunidad de Madrid (S2013/MIT-2740). P.B.-A. acknowledges funding support from the Discovery Grant Program of CRSNG and J.C.C. thanks the DFG and SFB767 for sponsoring his stay at the University of Konstanz as Mercator Fellow.

A nanostructured Ni-Fe-W powder was obtained by electrodeposition from ammonium citrate electrolyte within the current density range of 500-1000 mA cm(-2) at the electrolyte temperature of 50 degrees C -70 degrees C. XRD analysis shows that the powder contains an amorphous matrix having embedded nanocrystals of the FCC solid solution of iron and tungsten in nickel, with an average crystal grain size of 3.4 nm, a high internal microstrain value and a high density of chaotically distributed dislocations. EDS analysis exhibits that the chemical composition of the Ni-24%Fe-11%W powder does not depend upon current density and electrolyte temperature due to the diffusion control of the process of code-position of nickel, iron and tungsten. SEM micrographs show that the electrodeposition results in the formation of two particle shapes: large cauliflower-like particles and small dendrite particles. The cauliflower-like particles contain deep cavities at hydrogen evolution sites. Cavity density increases with increasing deposition current density. Smaller powder particles are formed at higher temperatures and at higher current densities. During the first heating, relative magnetic permeability decreases reaching the Curie temperature at about 350 degrees C and after cooling exhibits a 12% increase due to the performed relaxation process. Following the second heating to 500 degrees C, the magnetic permeability of the powder is about 5% lower than that of the as-prepared powder due to crystallization of the amorphous phase of the powder and the crystal grain growth in FCC phase.