Long-Range Phonon Spin Transport in Ferromagnet–Nonmagnetic Insulator Heterostructures

Abstract

We investigate phonon spin transport in an insulating ferromagnet−nonmagnet−ferromagnet heterostructure. We show that the magnetoelastic interaction between the spins and the phonons leads to nonlocal spin transfer between the magnets. This transfer is mediated by a local phonon spin current and accompanied by a phonon spin accumulation. The spin conductance depends nontrivially on the system size, and decays over millimeter length scales for realistic material parameters, far exceeding the decay lengths of magnonic spin currents.

Spin-lattice dynamics model with angular momentum transfer for canonical and microcanonical ensembles

“…With the increased volume of data stored, field-free, heat-free switching of magnetic bits could represent the future of energy efficient recording media applications. Another possible application is more advanced modeling of the ultrafast Einstein-de-Haas effect 2 or phonon-spin transport 77 .…”

Nonreciprocal surface magnetoelastic dynamics

“…Long-wavelength dipolar spin waves in the magnetic insulator-yttrium iron garnet (YIG)-can even travel over centimeters [6], but they suffer from a low group velocity; exchange spin waves have a large group velocity but their lifetime is shorter [7][8][9][10]. Recent studies showed that bulk phonons in the insulator gadolinium gallium garnet (GGG) can couple two YIG magnetic layers over millimeters [11][12][13][14], raising the possibility of using phonon currents to transfer spin information in nonmagnetic insulators. The surface (Rayleigh) acoustic waves (SAWs), known as excellent sources to pump spin waves via acoustic spin pumping [15][16][17][18][19][20][21], can propagate a longer distance with a larger group velocity [22,23] and thus is promising to transport spin information.…”

Unidirectional Pumping of Phonons by Magnetization Dynamics

“…The phonon pumping [17], i.e., the excitation of bulk sound waves in a high-quality acoustic insulator by the dynamics of a proximity magnetic layer via the magnetoelastic coupling [18,19], may be useful here. Bulk phonons in the insulator gadolinium gallium garnet (GGG) can couple two yttrium iron garnet (YIG) magnetic layers over millimeters [20,21].…”

“…For an analytical treatment, d is assumed to be much smaller than the skin depth of the SAWs, such that the displacement field in the wire is nearly uniform in the z dependence. The lattice and elastic parameters at the YIGjGGG interface match well [17,20,21,36] and are assumed equal. A uniform and sufficiently large static magnetic field H 0 along ⃗…”

“…In YIG films the magnetocrystalline anisotropy, which is important in CoFeB [12,43], is relatively weak [17,21,36] and the (linearized) magnon-phonon coupling energy is dominated byĤ m c ¼ ðB…”