The review presents the recent advances in small-angle scattering techniques for the characterization of magnetic nanoparticles and highlights the potential of these methods to facilitate the application-oriented nanoparticle design & synthesis.

In this paper a detailed numerical study (in frames of the Slonczewski formalism) of magnetization oscillations driven by a spin-polarized current through a thin elliptical nanoelement is presented. We show that a sophisticated micromagnetic model, where a polycrystalline structure of a nanoelement is taken into account, can explain qualitatively all most important features of the magnetization oscillation spectra recently observed experimentally [S. I. Kiselev et al., Nature 425, 380 (2003)], namely, existence of several equidistant spectral bands, sharp onset and abrupt disappearance of magnetization oscillations with increasing current, absence of the out-of-plane regime predicted by a macrospin model, and the relation between frequencies of so-called small-angle and quasichaotic oscillations. However, a quantitative agreement with experimental results (especially concerning the frequency of quasichaotic oscillations) could not be achieved in the region of reasonable parameter values, indicating that further model refinement is necessary for a complete understanding of the spin-driven magnetization precession even in this relatively simple experimental situation.

We investigate analytically and numerically nonlinear vortex spin torque oscillator dynamics in a circular magnetic nanodot induced by a spin-polarized current perpendicular to the dot plane. We use a generalized nonlinear Thiele equation including spin-torque term by Slonczewski for describing the nanosize vortex core transient and steady orbit motions and analyze nonlinear contributions to all forces in this equation. Blue shift of the nano-oscillator frequency increasing the current is explained by a combination of the exchange, magnetostatic, and Zeeman energy contributions to the frequency nonlinear coefficient. Applicability and limitations of the standard nonlinear nano-oscillator model are discussed.

We present numerical simulation studies of the steady-state magnetization dynamics driven by a spin-polarized current in a point-contact geometry for the case of a relatively large contact diameter $\left(D_{\text{c}}=80\text{nm}\right)$ and small external field $\left(H=30\text{Oe}\right)$. We show that under these conditions the magnetization dynamics is qualitatively different from the dynamics observed for small contacts in large external fields. In particular, the “bullet” mode with a relatively homogeneous mode core, which was the dominating localized mode for small contacts, is not found here. Instead, all localized oscillation modes observed in simulations correspond to different motion kinds of vortex-antivortex (V-AV) pairs. These modes include rotation of pairs with the V-AV distance $d\sim D_{\text{c}}$ and creation/annihilation of much smaller (satellite) V-AV pairs. We also show that for our geometry the Oersted field has a qualitative effect on the magnetization dynamics of a free layer. This effect offers (in principle) a possibility to control magnetization dynamics by a suitable electric contact setup, adjusted to produce a desired Oersted field. Finally, we demonstrate that when the magnetization dynamics of the “fixed” layer—induced by the magnetodipolar interaction with the ‘‘free’’ layer—is taken into account, the threshold current for the oscillation onset is drastically reduced and new types of localized modes appear. In conclusion, we show that our simulations reproduce semiquantitatively several important features of the magnetization dynamics in a point-contact system for low external fields reported experimentally.