Chiral excitation of spin waves in ferromagnetic films

We theoretically investigate the interlayer dipolar and exchange couplings for an array of metallic magnetic nanowires grown on top of an extended ultrathin yttrium iron garnet film. The calculated interlayer dipolar coupling agrees with observed anticrossings [Chen \emph{et al.}, Phys. Rev. Lett. \textbf{120}, 217202 (2018)], concluding that the interlayer exchange coupling is suppressed by a spacer layer between the nanowires and film. The Kittel mode in the nanowire array couples chirally to spin waves in the film, even though Damon-Eshbach surface modes do not exist. The chirality is suppressed when the interlayer exchange coupling becomes strong.Comment: 13 pages, 5 figure

Excitation of unidirectional exchange spin waves by a nanoscale magnetic grating

Magnon spintronics is a prosperous field that promises beyond-CMOS technology based on elementary excitations of the magnetic order that act as information carriers for future computational architectures. Unidirectional propagation of spin waves is key to the realization of magnonic logic devices. However, previous efforts to enhance the Damon-Eshbach-type nonreciprocity did not realize (let alone control) purely unidirectional propagation. Here we experimentally demonstrate excitations of unidirectional exchange spin waves by a nanoscale magnetic grating consisting of Co nanowires fabricated on an ultrathin yttrium iron garnet film. We explain and model the nearly perfect unidirectional excitation by the chirality of the magneto-dipolar interactions between the Kittel mode of the nanowires and the exchange spin waves of the film. Reversal of the magnetic configurations of film and nanowire array from parallel to antiparallel changes the direction of the excited spin waves. Our results raise the prospect of a chiral magnonic logic without the need for fragile surface states

Record thermopower found in an IrMn-based spintronic stack

The Seebeck effect converts thermal gradients into electricity. As an approach to power technologies in the current Internet-of-Things era, on-chip energy harvesting is highly attractive, and to be effective, demands thin film materials with large Seebeck coefficients. In spintronics, the antiferromagnetic metal IrMn has been used as the pinning layer in magnetic tunnel junctions that form building blocks for magnetic random access memories and magnetic sensors. Spin pumping experiments revealed that IrMn Néel temperature is thickness-dependent and approaches room temperature when the layer is thin. Here, we report that the Seebeck coefficient is maximum at the Néel temperature of IrMn of 0.6 to 4.0 nm in thickness in IrMn-based half magnetic tunnel junctions. We obtain a record Seebeck coefficient 390 (±10) μV K-1 at room temperature. Our results demonstrate that IrMn-based magnetic devices could harvest the heat dissipation for magnetic sensors, thus contributing to the Power-of-Things paradigm

Short-Wavelength Spin Waves in Yttrium Iron Garnet Micro-Channels on Silicon

Yttrium iron garnet (YIG) has been widely used in spin wave studies thanks to its low Gilbert damping constant. However, most high-quality YIG films are grown on gadolinium gallium garnet (GGG) substrate, which makes it difficult to integrate with existing semiconductor technology. We show spin wave excitation in a nanometer-thick YIG micro-channel on silicon substrate. The YIG is grown by pulsed laser deposition (PLD) in high-purity oxygen followed by rapid thermal annealing at 800 degrees C after deposition. Using meander coplanar waveguides at submicrometer scale, spin waves with wavelength down to 1 mu m are excited. By measuring the linewidth of the spin wave reflection spectra, a Gilbert damping constant alpha = 1.9 x 10(-3) was obtained

Nonreciprocal coherent coupling of nanomagnets by exchange spin waves

Nanomagnets are widely used to store information in non-volatile spintronic devices. Spin waves can transfer information with low-power consumption as their propagations are independent of charge transport. However, to dynamically couple two distant nanomagnets via spin waves remains a major challenge for magnonics. Here we experimentally demonstrate coherent coupling of two distant Co nanowires by fast propagating spin waves in an yttrium iron garnet thin film with sub-50 nm wavelengths. Magnons in two nanomagnets are unidirectionally phase-locked with phase shifts controlled by magnon spin torque and spin-wave propagation. The coupled system is finally formulated by an analytical theory in terms of an effective non-Hermitian Hamiltonian. Our results are attractive for analog neuromorphic computing that requires unidirectional information transmission. [Figure not available: see fulltext.]</p

Chiral excitation of spin waves in ferromagnetic films by magnetic nanowire gratings

We theoretically investigate the interlayer dipolar and exchange couplings between an array of metallic magnetic nanowires grown on top of an extended ultrathin yttrium iron garnet film. The calculated interlayer dipolar coupling agrees with observed anticrossings [Chen et al., Phys. Rev. Lett. 120, 217202 (2018)PRLTAO0031-900710.1103/PhysRevLett.120.217202], concluding that the interlayer exchange coupling is suppressed by a spacer layer between the nanowires and film for Ni, but not necessarily for Co. The Kittel mode in the nanowire array couples chirally to spin waves in the film, even though Damon-Eshbach surface modes do not exist. The chirality can be suppressed by a strong interlayer exchange coupling.QN/Bauer GroupQN/Blanter Grou