Magnon trap by chiral spin pumping

Abstract

Chiral spin pumping is the generation of a unidirectional spin current in half of ferromagnetic films or conductors by dynamic dipolar stray fields from close-by nanomagnets. We formulate a general theory of long-range chiral interactions between magnets mediated by unidirectional traveling waves, e.g., spin waves in a magnetic film or microwaves in a waveguide. The traveling waves emitted by an excited magnet can be perfectly trapped by a second, initially passive magnet by a dynamical interference effect. When both magnets are excited by a uniform microwave, the chiral interaction between them creates a large imbalance in their magnon numbers.

Nonreciprocal surface magnetoelastic dynamics

“…This can be observed by a wire with a high magnetic quality 2α G ω K |g k | 2 /c r , leading to ξ = e iπ , i.e., without amplitude suppression but a pure phase shift. When 2α G ω K → |g k | 2 /c r , the transmission tends to be zero and the energy accumulates in the magnet [46]. Finally, when 2α G ω K |g k | 2 /c r , ξ → 1 and the modulation vanishes and the phonon diode effect is very small.…”

“…is interpreted by a non-Hermitian Hamiltonian that describes the dissipatively coupled magnons [27,32,36,46]. Note that the coupling constant (ω) still depends on the frequency.…”

“…The phonon transmission can thus demonstrate the existence and information of the collective mode of many magnetic wires. Many properties of the collective mode were addressed in our previous works [36,46]. We numerically diagonalize the non-Hermitian Hamiltonian and calculate the phonon transmission through a magnetic array with distance δ between the neighboring wires.…”

“…are the demagnetization constants with the nanowire width w and thickness d [29,46]. Here the demagnetization factors are treated to be uniform across the wire by disregarding their spatial variation at the edges of nanowires.…”

“…The traveling waves mediate a long-range nonreciprocal interaction between remote magnets and the spin accumulates at the edge of magnets by the non-Hermitian skin effect [43][44][45]. Interference effect in nonreciprocal systems can directionally amplify or trap the traveling waves [46,47].…”