Inhomogeneous magnetoelastic states and magnetoelastic wave spectrum in a system consisting of magnetic/nonmagnetic multilayers

Abstract

A study is made of the magnetoelastic (ME) wave spectrum and ME superstructure nucleation in a system consisting of magnetic/nonmagnetic multilayers. A case of rhombic ferromagnetic layers with the hard magnetization axis $\stackrel{\ensuremath{\rightarrow}}{b}$ perpendicular to the layer surface is considered. We show that close to the phase transition associated with the spin reorientation in the layer plane, a ME wave with a horizontal polarization, propagating parallel to the layer plane, becomes unstable. The shear ME wave frequency and group velocity vanish for a finite value of a wave vector, and the wave becomes frozen, forming a ME domain structure localized near the layer interfaces. Existence of a new modulated phase is associated with a ME coupling of the magnetization to lattice deformation on the layer interfaces. The spectra of the surface ME in the homogeneous and modulated phases are calculated. Depending on the magnetic and nonmagnetic layer thickness and temperature, the stability regions of homogeneous collinear $(\stackrel{\ensuremath{\rightarrow}}{M}\ensuremath{\parallel}\stackrel{\ensuremath{\rightarrow}}{a})$ and angular phases and the ME domain structure are found, where $\stackrel{\ensuremath{\rightarrow}}{M}$ is the magnetization, and $\stackrel{\ensuremath{\rightarrow}}{a}$ is the easy orthorhombic axis direction. The calculation is extended to study the ME wave propagation in the systems consisting of two-sublattice orthoferrite/nonmagnetic multilayers.