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Ieda, Junichi; Matsuo, Mamoru*; Saito, Eiji; Maekawa, Sadamichi
no journal, ,
In 1915, Einstein, de Haas, and Barnett unveiled the relation between magnetism and rotational motion. Recent developments of nanofabrication technology and spintronics have enabled us to exchange the angular momentum among conduction electron spin, magnetization, and photon polarization. In this stream, a remaining form of angular momentum carried by condensed matter systems is a mechanical torque due to rotation of a rigid body. However, the relation between the mechanical rotation and spin currents has been elusive. To describe the direct coupling, we have constructed the fundamental Hamiltonian from the general relativistic Dirac equation, and have predicted spin current generation from a rigid rotation in a ballistic system. Those results are then extended to the diffusive regime. We also discuss spin-dependent transport due to linear acceleration.
Yamane, Yuta; Ieda, Junichi; Oe, Junichiro*; Barnes, S. E.*; Maekawa, Sadamichi
no journal, ,
Adachi, Hiroto; Oe, Junichiro*; Takahashi, Saburo; Maekawa, Sadamichi
no journal, ,
The spin Seebeck effect, i.e., the generation of the spin voltage by a temperature gradient, is now established as an universal aspect of ferromagnets as it is observed in several ferromagnetic materials ranging from metallic ferromagnet Ni
Fe
and semiconducting ferromagnet GaMnAs to an insulating magnet LaY
Fe
O
. Recent theoretical and experimental efforts have clarified that the phonon degrees of freedom is of crucial importance in the spin Seebeck effect. Here we theoretically discuss the phonon-drag contribution to the spin Seebeck effect; the spin Seebeck effect is enormously enhanced by nonequilibrium phonons that drag the low-lying spin excitations. This scenario predicts that the spin Seebeck signal at low temperature tracks the phonon-dominated thermal conductivity of the system, and the predicted behaviour has been confirmed by the recent experiments for yttrium iron garnet and for GaMnAs.