Ferromagnetic resonance driven spin pumping, a topic of steadily increasing interest since its emergence over two decades ago, remains one of the most exciting research fields in condensed matter ...physics. Among the many materials that have been explored for spin pumping, yttrium iron garnet (YIG) is one of the most extensively studied because of its exceptionally low magnetic damping and insulating nature. There is a great amount of literature in the spin pumping and related research fields, too broad for this review to cover. In this Topical Review, we focus on the YIG-based spin pumping results carried out by our groups, including: the mechanism and technical details of our off-axis sputtering technique for the growth of single-crystalline YIG epitaxial films with a high degree ordering, experimental evidence for the high quality of the YIG films, spin pumping results from YIG into various transition metals and their heterostructures, dynamic spin transport in YIG/antiferromagnet hybrid structures, intralayer spin pumping by localized spin wave modes confined by a micromagnetic probe, dynamic spin coupling between YIG and nitrogen-vacancy centers in diamond, parametric spin pumping from high-wavevector spin waves in YIG, and localized spin wave mode behavior in broadly tunable spatially complex magnetic configurations. These results build on the power and versatility of YIG spin pumping to improve our understanding of spin dynamics, spin currents, spin Hall physics, spin-orbit coupling, dynamic magnetic coupling, and the relationship between these phenomena in a broad range of materials, geometries, and settings.
We observe highly efficient dynamic spin injection from Y3Fe5O12 (YIG) into NiO, an antiferromagnetic (AF) insulator, via strong coupling, and robust spin propagation in NiO up to 100-nm thickness ...mediated by its AF spin correlations. Strikingly, the insertion of a thin NiO layer between YIG and Pt significantly enhances the spin currents driven into Pt, suggesting exceptionally high spin transfer efficiency at both YIG/NiO and NiO/Pt interfaces. This offers a powerful platform for studying AF spin pumping and AF dynamics as well as for exploration of spin manipulation in tailored structures comprising metallic and insulating ferromagnets, antiferromagnets, and nonmagnetic materials.
We report a systematic study of spin transport in antiferromagnetic (AF) insulators having a wide range of ordering temperatures. Spin current is dynamically injected from Y sub(3)Fe sub(5)O sub(12) ...(YIG) into various AF insulators in Pt/insulator/YIG trilayers. Robust, long-distance spin transport in the AF insulators is observed, which shows a strong correlation with the A F ordering temperatures. We find a striking linear relationship between the spin decay length in the AFs and the damping enhancement in YIG, suggesting the critical role of magnetic correlations in the AF insulators as well as at the AF/YIG interfaces for spin transport in magnetic insulators.
We lay the foundation for determining the microscopic spin interactions in two-dimensional (2D) ferromagnets by combining angle-dependent ferromagnetic resonance (FMR) experiments on high quality ...CrI3 single crystals with theoretical modeling based on symmetries. We discover that the Kitaev interaction is the strongest in this material with K ∼ − 5.2 meV , 25 times larger than the Heisenberg exchange J ∼ − 0.2 meV , and responsible for opening the ∼ 5 meV gap at the Dirac points in the spin-wave dispersion. Furthermore, we find that the symmetric off-diagonal anisotropy Γ ∼ − 67.5 μ eV , though small, is crucial for opening a ∼ 0.3 meV gap in the magnon spectrum at the zone center and stabilizing ferromagnetism in the 2D limit. The high resolution of the FMR data further reveals a μ eV -scale quadrupolar contribution to the S = 3 / 2 magnetism. Our identification of the underlying exchange anisotropies opens paths toward 2D ferromagnets with higher TC as well as magnetically frustrated quantum spin liquids based on Kitaev physics.
We have investigated spin pumping from Y3Fe5O12 thin films into Cu, Ag, Ta, W, Pt, and Au with varying spin-orbit coupling strengths. From measurements of Gilbert damping enhancement and inverse spin ...Hall signals spanning 3 orders of magnitude, we determine the spin Hall angles and interfacial spin mixing conductances for the six metals. The spin Hall angles largely vary as Z(4) (Z: atomic number), corroborating the role of spin-orbit coupling. Amongst the four 5d metals, the variation of the spin Hall angle is dominated by the sensitivity of the d-orbital moment to the d-electron count, confirming theoretical predictions.
Y3Fe5O12 is arguably the best magnetic material for magnonic quantum information science (QIS) because of its extremely low damping. We report ultralow damping at 2 K in epitaxial Y3Fe5O12 thin films ...grown on a diamagnetic Y3Sc2Ga3O12 substrate that contains no rare-earth elements. Using these ultralow damping YIG films, we demonstrate for the first time strong coupling between magnons in patterned YIG thin films and microwave photons in a superconducting Nb resonator. This result paves the road toward scalable hybrid quantum systems that integrate superconducting microwave resonators, YIG film magnon conduits, and superconducting qubits into on-chip QIS devices.
Ferroelectric ferromagnets are exceedingly rare, fundamentally interesting multiferroic materials that could give rise to new technologies in which the low power and high speed of field-effect ...electronics are combined with the permanence and routability of voltage-controlled ferromagnetism. Furthermore, the properties of the few compounds that simultaneously exhibit these phenomena are insignificant in comparison with those of useful ferroelectrics or ferromagnets: their spontaneous polarizations or magnetizations are smaller by a factor of 1,000 or more. The same holds for magnetic- or electric-field-induced multiferroics. Owing to the weak properties of single-phase multiferroics, composite and multilayer approaches involving strain-coupled piezoelectric and magnetostrictive components are the closest to application today. Recently, however, a new route to ferroelectric ferromagnets was proposed by which magnetically ordered insulators that are neither ferroelectric nor ferromagnetic are transformed into ferroelectric ferromagnets using a single control parameter, strain. The system targeted, EuTiO3, was predicted to exhibit strong ferromagnetism (spontaneous magnetization, ∼7 Bohr magnetons per Eu) and strong ferroelectricity (spontaneous polarization, ∼10 µC cm−2) simultaneously under large biaxial compressive strain. These values are orders of magnitude higher than those of any known ferroelectric ferromagnet and rival the best materials that are solely ferroelectric or ferromagnetic. Hindered by the absence of an appropriate substrate to provide the desired compression we turned to tensile strain. Here we show both experimentally and theoretically the emergence of a multiferroic state under biaxial tension with the unexpected benefit that even lower strains are required, thereby allowing thicker high-quality crystalline films. This realization of a strong ferromagnetic ferroelectric points the way to high-temperature manifestations of this spin-lattice coupling mechanism. Our work demonstrates that a single experimental parameter, strain, simultaneously controls multiple order parameters and is a viable alternative tuning parameter to composition for creating multiferroics.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
•Growth of epitaxial Y3Fe5O12 thin films on diamagnetic Y3Sc2.5Al2.5O12 buffer layer on Gd3Ga5O12 substrates.•Characterization of magnetic damping of Y3Fe5O12/Y3Sc2.5Al2.5O12 bilayers and a Y3Fe5O12 ...single layer at various temperatures and frequencies.•Observation of significantly narrower ferromagnetic resonance linewidths and lower damping in the Y3Fe5O12/Y3Sc2.5Al2.5O12 bilayers on Gd3Ga5O12 at low temperatures, as compared to those of Y3Fe5O12 films directly grown on Gd3Ga5O12.
Y3Fe5O12 (YIG) thin films are typically grown on Gd3Ga5O12 (GGG) substrates; however, such YIG thin films typically suffer from significantly increased damping at low temperatures due to the interfacial exchange coupling between the YIG magnetization and the lossy Gd3+ moments in GGG. To overcome this problem, we grow high-quality epitaxial YIG(35 nm) films on a thin diamagnetic Y3Sc2.5Al2.5O12 (YSAG) bilayer on GGG, where the YSAG buffer layer eliminates the exchange coupling between YIG and GGG. As a result, we obtain a much-improved damping of 1.2 × 10-3 at 2–5 K.
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