Recent years have witnessed a rapidly growing interest in exploring the use of spin waves for information transmission and computation toward establishing a spin-wave-based technology that is not only significantly more energy efficient than the CMOS technology, but may also cause a major departure from the von-Neumann architecture by enabling memory-in-logic and logic-in-memory architectures. A major bottleneck of advancing this technology is the excitation of spin waves with short wavelengths, which is a must because the wavelength dictates device scalability. Here, we report the discovery of an approach for the excitation of nm-wavelength spin waves. The demonstration uses ferromagnetic nanowires grown on a 20-nm-thick Y3Fe5O12 film strip. The propagation of spin waves with a wavelength down to 50 nm over a distance of 60,000 nm is measured. The measurements yield a spin-wave group velocity as high as 2600 m s−1, which is faster than both domain wall and skyrmion motions.
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 IrMnbased magnetic devices could harvest the heat dissipation for magnetic sensors, thus contributing to the Power-of-Things paradigm.
Spin
waves or their quanta magnons raise the prospect to act as
information carriers in the absence of Joule heating. The challenge
to excite spin waves with nanoscale wavelengths free of nanolithography
becomes a critical bottleneck for the application of nanomagnonics.
Magnetic skyrmions are chiral magnetic textures at the nanoscale.
In this work, short-wavelength exchange spin waves are demonstrated
to be chirally emitted in a low damping magnetic insulating thin film
by magnetic skyrmions. The spin-wave chirality originates from the
chiral spin pumping effect and is determined by the cross product
of the magnetization orientation and the film normal direction. The
Halbach effect explains the enhancement or attenuation of the spin-wave
amplitude with a reversed sign of the Dyzaloshinskii–Moriya
interaction. Controllable spin-wave propagation is demonstrated by
rotating a moderate applied field. Our findings are key for building
compact low-power nanomagnonic devices based on intrinsic nanoscale
magnetic textures.
The anomalous Nernst effect in a perpendicularly magnetized Ir22Mn78/Co20Fe60B20/MgO thin film is measured using well-defined in-plane temperature gradients. The anomalous Nernst coefficient reaches 1.8 μV/K at room temperature, which is almost 50 times larger than that of a Ta/Co20Fe60B20/MgO thin film with perpendicular magnetic anisotropy. The anomalous Nernst and anomalous Hall results in different sample structures revealing that the large Nernst coefficient of the Ir22Mn78/Co20Fe60B20/MgO thin film is related to the interface between CoFeB and IrMn.
Topological quantum materials have stimulated growing attention because they reveal novel aspects of condensed matter physics and point to new opportunities in materials science, in particular for thermoelectrics. Here, we experimentally study thermoelectric effects in HfTe 5 , which was predicted to be at the boundary between strong and weak topological insulators. The magnetic field dependence of HfTe 5 thermoelectric properties attests to the anomalous character of this material, supported by our angle-resolved photoemission spectroscopy (ARPES) measurements. At 36 K, the thermopower of −277 μV/K is reached when a field of 0.4 Tesla is applied, while it is −157 μV/K at zero field and a large Nernst coefficient up to 600 μV/K is observed at 100 K with magnetic field of 4 T. A possible topologically nontrivial band structure is proposed to account for our observations. Our results constitute a highly constraining set of data for any model of transport based on HfTe 5 band structure. Furthermore, the extraordinary thermoelectric properties suggest a new paradigm for the development of thermoelectric applications based on layered transition-metal chalcogenides.
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