magnetoacoustic shear waves in orthoferrite plates

Russian Physics Journal, Vol. 51, No. 11, 2008

MAGNETOACOUSTIC SHEAR WAVES IN ORTHOFERRITE PLATES E. А. Zhukov, A. P. Kuz’menko, and S. М. Burkov

UDC 537.622: 537.326

Keywords: domain boundary, magnetoacoustic shear waves, surface spin waves.

The velocity v of domain boundaries (DB) motion in weakly ferromagmetic orthoferrites (RFeO3 oxide compounds, where R denotes Y or a rare-earth element [1–3]) can exceed by several times the velocities of transverse (st) and longitudinal sound waves (sl), reaching a maximum value c (for YFeO3, st = 4.2⋅105 cm/s, sl = 7⋅105 cm/s, and c = 20⋅105 cm/s). Moreover, on field dependences of the velocity v(H), the shear magnetic fields H are recorded for which the DB velocity remains constant [2], and the DB dynamics depends on the sample thickness [4]. To describe the mechanisms of DB deceleration, a number of assumptions taking into account excitation of bulk magnetoacoustic waves [1] and Winter magnons [5] have been put forward. However, a complete and consistent explanation of the observed specific features in the behavior of v(H) during DB motion in orthoferrites has been lacking. In the present work, results of investigations of the magnetoacoustic shear waves in orthoferrite plates which can influence the DB dynamics are presented. 16 Let us consider orthoferrite of crystal chemical symmetry D2h possessing a weak ferromagnetic moment in the magnetic phase Г4 with spin configuration GxFz. This situation is typical for Y, Lu, and La orthoferrites at room temperature and for Dy, Tm, Eu, and some others at not too low temperatures [2, 3]. In the two-sublattice approximation, the magnetization vectors m = (M1 + M2)/2M and the antiferromagnetism vectors l = (M1 – M2)/2M, where M1 and M2 are sublattice magnetization vectors and M 12 = M 22 = M 2 , are related by expressions ml = 0 and m2 + l 2 = 1. We choose the coordinate axes x, y, and z coincident with the crystallographic axes a, b, and c. The vectors m and l in the equilibrium state are oriented along z and x axes, respectively. In fields smaller than the flip-flop ones, m2