Conservation of angular momentum and spin-currents in
magnetic systems.
S.O. Demokritov
Institute for Applied Physics, Muenster University, Germany,
Spin-currents - the flow of angular momentum without the
simultaneous transfer of electrical charge - play an enabling
role in the field of spintronics. Unlike the charge current, the
spin-current is not a conservative quantity within the spin
subsystem. This is due to the presence of the spin–orbit or
magnetic dipole interactions that couple the spin subsystem to
the lattice. In dynamic effects the spin–lattice coupling
usually acts as the source of damping: the precessing magnetic
moment experiences a torque towards its equilibrium orientation;
correspondingly the angular momentum in flows from the spin
subsystem into the lattice causing reduction of the precession
amplitude and the spin current.
I will show that in some specific cases this flow can be
reversed. We experimentally demonstrate that one can achieve an
amplification of the spin current in YIG/Pt layered system using
the three-magnon splitting process. This mechanism triggers
angular momentum transfer from the lattice to the magnetic
subsystem [1].
The interaction of spin-currents with thermal fluctuations in
NiFe created in NiFe/Pt layered system by electric current
flowing in a Pt layer results in a suppression or amplification
of the fluctuations depending on the direction of the spincurrent from Pt to NiFe. Thus, it is experimentally shown using
spin-currents one can cool or heat magnetic subsystems [2].
1. H. Kurebayashi, O. Dzyapko, V.E. Demidov, D. Fang, A.J.
Ferguson, S.O. Demokritov, Nature Materials, 10 660 (2011)
2. V. E. Demidov, S. Urazhdin, E. R. J. Edwards, M. D. Stiles,
R. D. McMichael, S. O. Demokritov, Phys. Rev. Lett
107 107204
(2011)