Dipole-exchange spin waves in magnetic thin films at zero and finite temperature: Theory and simulations

Abstract

The excitation spectra in a stacked square lattice of dipole-exchange coupled classical spins is studied using both standard linearized spin-wave theory and the direct integration of the torque equation. A detailed comparison of the two methods is presented for the case of small-amplitude spin-wave modes. The spin-wave frequencies obtained from the time-dependent correlation functions calculated by integrating the equation of motion are shown to be in excellent agreement with the results obtained from linearized spin-wave theory for both single-layer and multilayer films. Applying the numerical integration method, the finite-temperature correlation function is calculated using Monte Carlo spin dynamics for the case of a single-layer, dipole-exchange coupled system. Values for the frequencies, amplitudes, and decay constant of the spin-wave modes at finite temperature are calculated from a spectral analysis of the finite-temperature correlation function. It is shown that thermal fluctuations give rise to a softening of the spin-wave frequencies and an intrinsic damping of the spin-wave oscillations.

Nematic order in a simple-cubic lattice-spin model with full-ranged dipolar interactions

“…Eqs. (3), ( 8) and (9) show that in all D (Θ, Φ) configurations the vector C 0 has the same modulus, and that each D(Θ, Φ) defines its possible orientation, or, in other words, the ground state exhibits full order and continuous degeneracy with respect to the above C 0 vector. Notice also that the above transformation from u j to w j unit vectors (Eq.…”

“…Long-range dipolar interactions [1] between magnetic moments are ubiquitous in experimentally studied magnetic systems, although often dominated by exchange couplings (for more details see Refs. [2][3][4][5] and references therein), and, over decades, a number of theoretical studies, based on Renormalization group techniques, has addressed interaction models containing both dipolar and short-range isotropic or anisotropic exchange interactions (see, e.g., Refs [2,[6][7][8][9][10][11]); on the other hand, lattice models involving only the longrange dipolar term have also long been studied by various approaches, including spin-wave treatments and simulation (see, e.g., Refs. [12][13][14][15][16][17][18][19], and others quoted in the following).…”

Dipolar ferromagnetism in three-dimensional superlattices of nanoparticles

“…This represents a more fundamental approach than the more phenomenological models composed of a system of coupled superspins [19][20][21][22] . The calculations were all performed using the micromagnetics scripting language MagLua 23 that has been successfully applied to a number of atomistic and micromagnetic simulation studies in nanomagnetism [24][25][26] .…”

Atomic level micromagnetic model of recording media switching at elevated temperatures

“…9,10 Solutions to the standard LLG equation with the stochastic thermal field were obtained using the Euler integration method with damping constant α = 0.1, a time step of 0.001 ps, and with rotations updated using a quaternions representation. 14 Magnetic parameters were based on generic single-layer FePt-type media with a saturation moment M s = 1000 emu/cc, inter-grain exchange was omitted and uniaxial anisotropy was K = 5 × 10 7 erg/cc, giving H K = 100 kOe. Note that our simulations require a zero temperature estimate of the anisotropy, which is nearly a factor of two larger than its value at 300 K. 15 We also tested our method on ultra-high H K = 250 kOe media (by reducing M s to 400 emu/cc).…”