Magnetoacoustic resonance in antiferromagnetic insulators in ‘‘moderate’’ and strong magnetic fields

Abstract

The magnetoacoustic resonance between phonons and magnons is studied analytically on the basis of a set of linearized magnetoelastic equations, which was previously deduced from a rotationally invariant nonlinear theory for uniaxial antiferromagnets of the easy-axis type. More specifically, the present paper investigates the less studied case where the bias magnetic field is either ‘‘moderate’’ or strong relative to some material parameter. Various types of dispersion and magnetoacoustic resonance couplings are exhibited depending on whether waves propagate along the direction of or orthogonal to the symmetry axis. In some cases a fast transverse elastic mode couples with both upper and lower magnon branches, while longitudinal and slow transverse elastic modes travel independently. In another case both fast and slow transverse elastic modes couple with both upper and lower magnon branches. In the case that most closely resembles the case of ferromagnets, left-circularly polarized transverse phonons and magnons couple at both high and low magnetoacoustic resonance points, while the right-circularly polarized transverse phonons are only rendered slightly dispersive for small wave numbers. These coupled dispersion behaviors are studied analytically (asymptotics) in terms of a small parameter which represents globally magnetoelastic couplings. This paper concludes the study of magnetoacoustic resonance in antiferromagnetic insulators which was started in a previous paper concerned with the case of weak bias magnetic fields.