Spontaneous Magnetization of the O(3) Ferromagnet at Low Temperatures

We investigate the low-temperature behavior of ferromagnets with a spontaneously broken symmetry O(3) $\to$ O(2). The analysis is performed within the perspective of nonrelativistic effective Lagrangians, where the dynamics of the system is formulated in terms of Goldstone bosons. Unlike in a Lorentz-invariant framework (chiral perturbation theory), where loop graphs are suppressed by two powers of momentum, loops involving ferromagnetic spin waves are suppressed by three momentum powers. The leading coefficients of the low-temperature expansion for the partition function are calculated up to order $p^{10}$. In agreement with Dyson's pioneering microscopic analysis of the cubic ferromagnet, we find that, in the spontaneous magnetization, the magnon-magnon interaction starts manifesting itself only at order $T^4$. The striking difference with respect to the low-temperature properties of the O(3) antiferromagnet is discussed from a unified point of view, relying on the effective Lagrangian technique.Comment: 23 pages, 4 figure

An analytical model of the vector digital magnetic recording process in isotropic thin media

publication-status: Publishedtypes: ArticleAn analytical theory has been produced for describing the vector nature of the digital magnetic recording process in thin-film isotropic media. It is based upon assumptions on the way in which the magnetization follows the field during the recording process and shows, except for a scaling of their peak values, that the longitudinal and perpendicular components of magnetization behave, respectively, as if they were separately present in a longitudinal and perpendicular recording. The magnitudes of the longitudinal and perpendicular magnetization components are derived in particular cases