Magnon-polarons in cubic collinear antiferromagnets

Abstract

We present a theoretical study of excitations formed by hybridization between magnons and phonons -magnonpolarons -in antiferromagnets. We first outline a general approach to determining which magnon and phonon modes can and cannot hybridize in a system thereby addressing the qualitative questions concerning magnonpolaron formation. As a specific and experimentally relevant case, we study Nickel Oxide quantitatively and find perfect agreement with the qualitative analysis, thereby highlighting the strength of the former. We find that there are two distinct features of antiferromagnetic magnon-polarons which differ from the ferromagnetic ones. First, hybridization between magnons and the longitudinal phonon modes is expected in many cubic antiferromagnetic structures. Second, we find that the very existence of certain hybridizations can be controlled via an external magnetic field, an effect which comes in addition to the ability to move the magnon modes relative to the phonons modes.arXiv:1812.09239v1 [cond-mat.mes-hall]

Dynamic magnetoelastic boundary conditions and the pumping of phonons

“…We can adopt MEC generated, e.g., by exchange [19] or interfacial Dzyaloshinskii-Moriya interaction [34,58] to address phonon pumping by spin waves and magnetorotation coupling in basically any material combination with ferromagnets. In principle, the analysis can also be extended to antiferromagnets [59][60][61][62][63], but the MEC energy and its parameters are less established. The magnon frequencies in antiferromagnets are typically higher than that of ultrasound [19,62] and magnonphonon hybridization requires application of large magnetic fields [63].…”

“…In principle, the analysis can also be extended to antiferromagnets [59][60][61][62][63], but the MEC energy and its parameters are less established. The magnon frequencies in antiferromagnets are typically higher than that of ultrasound [19,62] and magnonphonon hybridization requires application of large magnetic fields [63]. Large MEC coefficients and large magnetization amplitudes are important for phonon pumping.…”

Magnon polarons in the spin Peltier effect

“…Magnetoelastic coupling (MEC), the interaction between spin waves (magnons) and lattice waves (phonons), was first investigated more than half a century ago [1][2][3] and has renewed attention in spintronics . By the MEC, magnons and phonons, in the vicinity of the crossings of their dispersion relations, are hybridized into quasiparticles called magnon polarons that share mixed magnonic and phononic characters [6,8,[10][11][12][20][21][22][23][24][25][26][27][28][29][30]. Magnon polarons can convey spin information with velocities close to those of phonons, much faster than the magnon velocities in the dipolar magnon regime [7,8,14,15].…”

Magnon-polarons in van der Waals antiferromagnet FePS3

“…4. To reproduce these data, we refer to a generic theoretical approach to the problem of magnon-phonon coupling [12,44] which in its complete form accounts for possible interactions between all relevant (dispersing with wavevector k) branches of magnon and phonon modes present in a magnetically ordered system overall described within the Heisenberg formalism [29]. This general approach is here simplified down to the phenomenological model.…”

“…Magnons (spin waves) and phonons (lattice vibrations) are two relevant, low energy excitations in magnetically ordered systems, and the coupling between these modes, otherwise central for the present work, has been a subject of numerous theoretical and experimental studies in various ferromagnetic [10,11], antiferromagnetic [12,13], ferrimagnetic [14,15] as well as in multiferroic [16] materials. Coupling between magnons and phonons affects the dynamical and optical properties of these quasi-particles and appears to be of special importance in emerging areas, such as, for example, spin caloritronics [17,18] or magnon spintronics in conjunction with new developments in terahertz (THz), technology [19,20].…”