Spin polarized current may transfer angular momentum to a ferromagnet, resulting in a spintorque phenomenon. At the same time the shot noise, associated with the current, leads to a non-equilibrium stochastic force acting on the ferromagnet. We derive stochastic version of LandauLifshitz-Gilbert equation for a magnetization of a "free" ferromagnetic layer in contact with a "fixed" ferromagnet. We solve the corresponding Fokker-Planck equation and show that the non-equilibrium noise yields to a non-monotonous dependence of the precession spectrum linewidth on the current.Magnetization dynamics of a ferromagnet under influence of a spin polarized current is a subject of intensive investigations (for recent reviews see Refs. [1,2]). It was realized [3,4] that the spin current may transfer the angular momentum to the ferromagnet, resulting in a torque acting on its magnetization direction. In the case of a small ferromagnetic domain the torque may lead to a rotation of the magnetization as a whole, rather than to an excitation of spin waves. This phenomenon, allowing for an electronic manipulation of the magnetization, has a promise for a number of potential applications.The effect has been recently observed [5,6,7,8,9] in a setup, where the spin-torque magnitude and direction are tuned to compensate exactly the dissipation force acting on the magnetization of the "free" ferromagnetic layer. This leads to an undamped precession which is detected through the induced microwave radiation. Both the spectral width and the generated power exhibit a strong dependence on the current flowing through the interface of the two ferromagnets. It was shown later [10,11] that the equilibrium thermal noise, first introduced in dynamics of micromagnets by F-L. Brown [12], may partially account for the observed linewidth.On the other hand, since the experiments are performed under non-equilibrium conditions (spin current strong enough to balance the dissipation), one needs to address non-thermal sources of noise as well. The most essential of them is the spin shot noise associated with the discreteness of spin passing through the interface. This phenomenon may be accounted for by adding a fluctuating part to the spin current vector in the Slonczewski's torque term of Landau-Lifshitz-Gilbert (LLG) equation I s → I s + δI s (t). The resulting stochastic LLG equation for the unit vector m = M/M in the direction of the magnetization M takes the formHere γ is gyromagnetic ratio, H eff = −∂F/∂M is the effective magnetic field, which includes both an external field and magnetic anisotropy, and V is a volume of the free ferromagnet. Gilbert damping α(θ) is renormalized by the coupling to the fixed ferromagnet [2,13] and is thus dependent on a relative orientation angle θ of the fixed and free ferromagnets. One could expect that the fluctuating part of the spin current vector δI s (t) is preferentially directed along the spin polarization of the incoming electron flux, i.e. along I s . This is not the case, however, due to the quantum nature o...

A two quantum-dot device is coupled in parallel for studying the competition between the pseudo-spin Kondo effect and strongly hybridized molecular states. Cryogenic measurements are performed in the regime of weak coupling of the two dots to lead states under linear transport conditions. Detailed simulations verify the finding of the transition between the two different regimes. 73.63.Kv,72.10.FK,

We present a generalization of the recently developed dualfermion approach introduced for correlated lattices to nonequilibrium problems. In its local limit, the approach has been used to devise an efficient impurity solver, the superperturbation solver for the Anderson impurity model (AIM). Here we show that the general dual perturbation theory can be formulated on the Keldysh contour. Starting from a reference Hamiltonian system, in which the timedependent solution is found by exact diagonalization, we make a dual perturbation expansion in order to account for the relaxation effects from the fermionic bath. Simple test results for closed as well as open quantum systems in a fermionic bath are presented.

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We investigate the role of equilibrium and nonequilibrium noise in the magnetization dynamics on mono-domain ferromagnets. Starting from a microscopic model we present a detailed derivation of the spin shot noise correlator. We investigate the ramifications of the nonequilibrium noise on the spin torque dynamics, both in the steady state precessional regime and the spin switching regime. In the latter case we apply a generalized Fokker-Planck approach to spin switching, which models the switching by an Arrhenius law with an effective elevated temperature. We calculate the renormalization of the effective temperature due to spin shot noise and show that the nonequilibrium noise leads to the creation of cold and hot spot with respect to the noise intensity.