The series decomposition of G(s) does not contain u 2-term; it contains only small c 2 u 2-term, G(u) = G(0)[1 - O(c 2 u 2)], although G(u) essentially decreases at large u, when the vortex core is close to be expelled from the dot [16]. The result of power decomposition of the total energy density is (4) and the coefficients are where , , , β = L/R, , and ς = 1 + 15(ln 2 - 1/2)R c /8R. There is an additional contribution to κ/2, 2(L e /R)2, due to the face magnetic charges essential for the nanodots with small R [27]. The contribution is

positive and ITF2357 mw can be accounted by calculating dependence of the equilibrium vortex core radius (c) on the vortex displacement. This dependence with high accuracy at cu < < 1 can be described by the function c(u) = c(0)(1 - u 2)/(1 + u 2). Here, c(0) is the equilibrium vortex core radius at s = 0, for instance

c(0) = 0.12 (R c  = 12 nm) for the nanodot buy GDC-0449 thickness L = 7 nm. The nonlinear vortex gyrotropic frequency can be written accounting Equation 4 as (5) where the linear gyrotropic frequency is ω 0 = γM s κ(β, R, J)/2, and N(β, R) = κ′(β, R)/κ(β, R). The frequency was calculated in [26] VX-689 and was experimentally and numerically confirmed in many papers. The nonlinear coefficient N(β,R) depends strongly on the parameters β and R, decreasing with β and R increasing. The typical values of N(β,R) at J = 0 are equal to 0.3 to 1. The last term in Equation 3 prevents its reducing to a nonlinear

oscillator equation nearly similar to the one used for the description of saturated STNO in [13]. Calculation within TVA yields the decomposition , where , i.e., the term containing d n (s) ≈ α G u 2 <<1 can be neglected. Then, substituting s = u exp(iΦ) to Equation 3, we get the system of coupled equations (6) Equation 3 and the system (6) are different from the system of equations of the nonlinear oscillator approach [13]. Equations 6 are reduced to the autonomous oscillator equations and only if the conditions d 2 < < 1 and dχ < < ω G are satisfied and we define the positive/negative damping parameters [13] as Γ +(u) = d(u)ω G (u) and Γ -(u) = χ(u). We note that reducing the Thiele equation (1) to a nonlinear oscillator equation [13] is possible only for axially symmetric nanodot, when the functions W(s), G(s), d(s) and χ(s) depend only on u = |s| and the additional conditions d n  < < 1, d 2 < < 1, and dχ < < ω G are satisfied. The nonlinear oscillator model [13] cannot be applied for other nanodot (free layer) shapes, i.e., elliptical, square, etc., whereas the generalized Thiele equation (1) has no such restrictions. The system (6) at yields the steady vortex oscillation solution u 0(J) > 0 as root of the equation χ(u 0) = d(u 0)ω G (u 0) for χ(0) > d(0)ω 0 (J > J c1) and u 0 = 0 otherwise.