Explosive instability of quasi-phonon triads in antiferromagnet under frequency modulated electromagnetic field

Three wave coupling and explosive instability of magneto-elastic excitations in FeBO3 single crystal

“…The influence of bias field on magnetoelastic resonance in FeBO 3 is similar to the same effect in hematite [3]; however unlike hematite iron borate does not have Morin spin reorientation transition at lower temperatures, so it was possible to decrease temperature (up to 77 K in our experiments). Maximum eigenfrequency change of the magneto-elastic oscillations in the field range 10 Oe-2 kOe at 293 K is less than 7%, while at 77 K it is 22%.…”

“…The technique that was used to study three quasi-phonon coupling in the iron borate sample is similar to the one that was previously developed for hematite [3]. The sample was excited with two subsequent electromagnetic pulses applied to the one of the crossed coils with the axis orientation under the angle 801 relatively to the bias field H. The first pulse was applied at the eigenfrequency o n of the selected mode ''n'' and created the initial number of quasi-phonons in the sample.…”

“…The vibrations of coupled elastic and magnetic subsystems in antiferromagnetic acoustic resonator of crystalline symmetry D 3d 6 and magnetic anisotropy of ''easy plane'' type are described by the system of equations [3] € a n þ 2d n _ a n þ o 2 n0 ða n þsin2jÞ ¼ 0, ð5Þ…”

“…The most suitable objects for studies of three quasi-phonon excitations are antiferromagnets of ''easy plane'' type (AFEP) due to extremely strong nonlinear interaction of quasi-phonons in such kind of magnetic crystals [1]. The coupling of three quasiphonons was observed recently in the ''easy plane'' phase of antiferromagnetic crystal a-Fe 2 O 3 under homogeneous RF electromagnetic pumping [2,3]. The theoretical analysis [2,4] has shown several specific dynamic features that differ the three wave coupling from well known parametric excitation of quasiphonon pairs.…”

“…It was shown also that the supercritical limitation of amplitudes of excited waves in a-Fe 2 O 3 crystal is caused first of all by the nonlinear frequency shift (NFS) of magneto-elastic modes [2]. Bright manifestations of the explosive instability in a-Fe 2 O 3 were achieved when NFS effect was compensated by the proper quasi-singular phase modulation of the pumping electromagnetic field [3].…”