Ludo Cornelissen

Long-distance transport of magnon spin information in a magnetic insulator at room temperature

Although electron motion is prohibited in magnetic insulators, the electron spin can be transported by magnons. Such magnons, generated and detected using all-electrical methods, are now shown to travel micrometre distances at room temperature. The transport of spin information has been studied in various materials, such as metals1, semiconductors2 and graphene3. In these materials, spin is transported by the diffusion of conduction electrons4. Here we study the diffusion and relaxation of spin in a magnetic insulator, where the large bandgap prohibits the motion of electrons. Spin can still be transported, however, through the diffusion of non-equilibrium magnons, the quanta of spin-wave excitations in magnetically ordered materials. Here we show experimentally that these magnons can be excited and detected fully electrically5,6,7 in a linear response, and can transport spin angular momentum through the magnetic insulator yttrium iron garnet (YIG) over distances as large as 40 μm. We identify two transport regimes: the diffusion-limited regime for distances shorter than the magnon spin diffusion length, and the relaxation-limited regime for larger distances. With a model similar to the diffusion–relaxation model for electron spin transport in (semi)conducting materials, we extract the magnon spin diffusion length λ = 9.4 ± 0.6 μm in a thin 200 nm YIG film at room temperature.

Magnon spin transport driven by the magnon chemical potential in a magnetic insulator

We develop a linear-response transport theory of diffusive spin and heat transport by magnons in magnetic insulators with metallic contacts. The magnons are described by a position-dependent temperature and chemical potential that are governed by diffusion equations with characteristic relaxation lengths. Proceeding from a linearized Boltzmann equation, we derive expressions for length scales and transport coefficients. For yttrium iron garnet (YIG) at room temperature we find that long-range transport is dominated by the magnon chemical potential. We compare the models results with recent experiments on YIG with Pt contacts [L. J. Cornelissen, Nat. Phys. 11, 1022 (2015)1745-247310.1038/nphys3465] and extract a magnon spin conductivity of σm=5×105 S/m. Our results for the spin Seebeck coefficient in YIG agree with published experiments. We conclude that the magnon chemical potential is an essential ingredient for energy and spin transport in magnetic insulators.

Magnetic field dependence of the magnon spin diffusion length in the magnetic insulator yttrium iron garnet

We investigated the effect of an external magnetic field on the diffusive spin transport by magnons in the magnetic insulator Y3Fe5O12, using a nonlocal magnon transport measurement geometry. We observed a decrease in magnon spin diffusion length lambda(m) for increasing field strengths, where lambda(m) is reduced from 9.6 +/- 1.2 mu m at 10 mT to 4.2 +/- 0.6 mu m at 3.5 T at room temperature. In addition, we find that there must be at least one additional transport parameter that depends on the external magnetic field. Our results do not allow us to unambiguously determine whether this is the magnon equilibrium density or the magnon diffusion constant. These results are significant for experiments in the more conventional longitudinal spin Seebeck geometry, since the magnon spin diffusion length sets the length scale for the spin Seebeck effect as well and is relevant for its understanding.

Temperature dependence of the magnon spin diffusion length and magnon spin conductivity in the magnetic insulator yttrium iron garnet

We present a systematic study of the temperature dependence of diffusive magnon spin transport using nonlocal devices fabricated on a 210-nm yttrium iron garnet film on a gadolinium gallium garnet substrate. In our measurements, we detect spin signals arising from electrical and thermal magnon generation, and we directly extract the magnon spin diffusion length

Influence of yttrium iron garnet thickness and heater opacity on the nonlocal transport of electrically and thermally excited magnons

{\ensuremath{\lambda}}_{m}

Nonlocal magnon-polaron transport in yttrium iron garnet

for temperatures from 2 to 293 K. Values of

Criteria for accurate determination of the magnon relaxation length from the nonlocal spin Seebeck effect

{\ensuremath{\lambda}}_{m}

Magnon planar Hall effect and anisotropic magnetoresistance in a magnetic insulator

obtained from electrical and thermal generation agree within the experimental error with

Nonlocal magnon spin transport in yttrium iron garnet with tantalum and platinum spin injection/detection electrodes

{\ensuremath{\lambda}}_{m}=9.6\ifmmode\pm\else\textpm\fi{}0.9\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{m}

Enhanced magnon spin transport in NiFe2O4 thin films on a lattice-matched substrate

at room temperature to a minimum of