Low Magnetic Damping Research Articles

Write-error reduction in voltage-driven magnetization switching using a recording layer with low magnetic damping

Write-error reduction in voltage-driven magnetization switching using a recording layer with low magnetic damping

Enhanced effective spin Hall efficiency contributed by the extrinsic spin Hall effect in Pt1- x Ta x /CoFeB structures

High effective spin Hall efficiency and low magnetic damping constant are essential to achieve efficient spin-charge conversion for energy-efficient spintronic devices. We report the measurements of effective spin Hall efficiency and magnetic damping constant of Pt1- x Ta x /CoFeB structures using spin-torque ferromagnetic resonance (ST-FMR) techniques. With the increase of Ta content, the spin Hall efficiency increases and peaks x = 0.15 with the value of θSHeff=0.35 , before decreases for further Ta content. This non-monotonic variation is attributed to the interaction between the contribution of the extrinsic skew scattering mechanism and the spin-orbit coupling (SOC). The weakening of the SOC in the Pt1-x Ta x layer leads to a decrease in the effective magnetic damping constant with increasing Ta concentration. High-temperature ST-FMR measurements confirm the influence of the Ta concentration on the spin Hall effect and magnetic damping mechanism. Additionally, the decrease in spin mixing conductance and the increase in spin diffusion length leads to a decrease in the interfacial spin transparency.

Aluminum substitution in low damping epitaxial lithium ferrite films

Ferromagnetic insulators with ultra-low damping and tunable magnetic properties are of great interest for the study of spin wave-based phenomena as well as for applications in spin wave spintronics. We have developed epitaxial spinel structure ferrite thin films of Li0.5(AlxFe2.5−x)O4 (LAFO) with ultra-low magnetic damping. The degree of Al substitution tunes the saturation magnetization and in-plane magnetic anisotropy while maintaining excellent epitaxy and crystalline quality as well as low magnetic damping. All LAFO films, deposited on (001)-oriented MgAl2O4 (MAO), are under epitaxial compressive strain, giving rise to an easy magnetic axis in-plane and a hard out-of-plane axis. Element-specific x-ray magnetic circular dichroism measurements confirm that the magnetism originates from the majority of Fe3+ cations occupying the octahedral sites, which are displaced by increased Al3+ substitution. Broadband ferromagnetic resonance reveals the lowest Gilbert damping parameters of 5×10−4 for films 10–15 nm thick. Our films demonstrate the robustness of the low loss dynamic properties of Li0.5(AlxFe2.5−x)O4 that are promising for spin wave applications.

Ultra-thin lithium aluminate spinel ferrite films with perpendicular magnetic anisotropy and low damping

Ultra-thin films of low damping ferromagnetic insulators with perpendicular magnetic anisotropy have been identified as critical to advancing spin-based electronics by significantly reducing the threshold for current-induced magnetization switching while enabling new types of hybrid structures or devices. Here, we have developed a new class of ultra-thin spinel structure Li0.5Al1.0Fe1.5O4 (LAFO) films on MgGa2O4 (MGO) substrates with: 1) perpendicular magnetic anisotropy; 2) low magnetic damping and 3) the absence of degraded or magnetic dead layers. These films have been integrated with epitaxial Pt spin source layers to demonstrate record low magnetization switching currents and high spin-orbit torque efficiencies. These LAFO films on MGO thus combine all of the desirable properties of ferromagnetic insulators with perpendicular magnetic anisotropy, opening new possibilities for spin based electronics.

Nonlinear three-magnon scattering in low-damping La0.67Sr0.33MnO3 thin films

Abstract Three-magnon scattering, a nonlinear process in which a high-energy magnon splits into two low-energy magnons with energy and momentum conservation, have been widely studied in magnonics community. Here, we report experimental observation of nonlinear three-magnon scattering in La0.67Sr0.33MnO3 thin films with low magnetic damping (~10-4) by all-electric and angle-resolved spin wave spectroscopy. The reflection spectra of the spin wave resonance with high excitation at Damon–Eshbach configuration demonstrate a scattering regime with gradual signal disappearance, where a magnon of Damon–Eshbach mode decays into two magnons of volume mode above threshold power (-10 dBm) of injected microwave. The nonlinear scattering is only allowed at low-field regime and calculated dispersions of dipole-exchange spin wave claim the mechanism of allowed and forbidden three-magnon scattering. The films and heterostructures of La0.67Sr0.33MnO3havebeenalready demonstrated with rich physical phenomena and great versatility, and the nonlinear magnetic dynamics of La0.67Sr0.33MnO3 thin films is revealed in this work, which offer more possibility of applications to oxide magnonics and nonlinear magnonic devices.

Electrical detection of spin pumping in van der Waals ferromagnetic Cr2Ge2Te6 with low magnetic damping

The discovery of magnetic order in atomically-thin van der Waals materials has strengthened the alliance between spintronics and two-dimensional materials. An important use of magnetic two-dimensional materials in spintronic devices, which has not yet been demonstrated, would be for coherent spin injection via the spin-pumping effect. Here, we report spin pumping from Cr2Ge2Te6 into Pt or W and detection of the spin current by inverse spin Hall effect. The magnetization dynamics of the hybrid Cr2Ge2Te6/Pt system are measured, and a magnetic damping constant of ~ 4–10 × 10−4 is obtained for thick Cr2Ge2Te6 flakes, a record low for ferromagnetic van der Waals materials. Moreover, a high interface spin transmission efficiency (a spin mixing conductance of 2.4 × 1019/m2) is directly extracted, which is instrumental in delivering spin-related quantities such as spin angular momentum and spin-orbit torque across an interface of the van der Waals system. The low magnetic damping that promotes efficient spin current generation together with high interfacial spin transmission efficiency suggests promising applications for integrating Cr2Ge2Te6 into low-temperature two-dimensional spintronic devices as the source of coherent spin or magnon current.

Negligible magnetic losses at low temperatures in liquid phase epitaxy grown Y3Fe5O12 films

Yttrium iron garnet (${\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$; YIG) has a unique combination of low magnetic damping, high spin-wave conductivity, and insulating properties that make it a highly attractive material for a variety of applications in the fields of magnetics and spintronics. While the room-temperature magnetization dynamics of YIG have been extensively studied, there are limited reports correlating the low-temperature magnetization dynamics to the material structure or growth method. Here we investigate liquid phase epitaxy grown YIG films and their magnetization dynamics at temperatures down to 10 K. We show there is a negligible increase in the ferromagnetic resonance linewidth down to 10 K, which is unique when compared with YIG films grown by other deposition methods. From the broadband ferromagnetic resonance measurements, polarized neutron reflectivity, and scanning transmission electron microscopy, we conclude that these liquid phase epitaxy grown films have negligible rare-earth impurities present, specifically the suppression of Gd diffusion from the ${\mathrm{Gd}}_{3}{\mathrm{Ga}}_{5}{\mathrm{O}}_{12}$ (GGG) substrate into the ${\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ film, and therefore negligible magnetic losses attributed to the slow-relaxation mechanism. Overall, liquid phase epitaxy YIG films have a YIG/GGG interface that is five times sharper and have ten times lower ferromagnetic resonance linewidths below 50 K than comparable YIG films by other deposition methods. Thus, liquid phase epitaxy grown YIG films are ideal for low-temperature experiments/applications that require low magnetic losses, such as quantum transduction and manipulation via magnon coupling.

Spin wave dispersion of ultra-low damping hematite ( α−Fe2O3 ) at GHz frequencies

Low magnetic damping and high group velocity of spin waves (SWs) or magnons are two crucial parameters for functional magnonic devices. Magnonics research on signal processing and wave-based computation at GHz frequencies focused on the artificial ferrimagnetic garnet ${\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ (YIG) so far. We report on spin wave spectroscopy studies performed on the natural mineral hematite ($\ensuremath{\alpha}{\text{-Fe}}_{2}{\text{O}}_{3}$), which is a canted antiferromagnet. By means of broadband GHz spectroscopy and inelastic light scattering, we determine a damping coefficient of $1.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ and magnon group velocities of a few 10 km/s, respectively, at room temperature. Covering a large regime of wave vectors up to $k\ensuremath{\approx}24\phantom{\rule{0.16em}{0ex}}\mathrm{rad}/\textmu{}\mathrm{m}$, we find the exchange stiffness length to be relatively short and only about 1 \AA{}. In a small magnetic field of 30 mT, the decay length of SWs is estimated to be 1.1 cm similar to the best YIG. Still, inelastic light scattering provides surprisingly broad and partly asymmetric resonance peaks. Their characteristic shape is induced by the large group velocities, low damping, and distribution of incident angles inside the laser beam. Our results promote hematite as an alternative and sustainable basis for magnonic devices with fast speeds and low losses based on a stable natural mineral.

Low magnetic damping in an ultrathin CoFeB layer deposited on a 300 mm diameter wafer at cryogenic temperature

We deposited an ultrathin CoFeB(1.1 nm) layer, which functions as a storage layer of MgO-based magnetic tunnel junctions for spin-transfer-torque (STT) magnetoresistive random-access memory (MRAM), on ϕ300 mm wafers at 100 K and investigated its effect on the magnetization dynamics of CoFeB. We observed clear reductions in both the inhomogeneous linewidth and total magnetic damping parameter for the CoFeB layer deposited at 100 K compared to those deposited at 300 K through the improvement in the interfacial quality. The results show that deposition at cryogenic temperatures is an effective manufacturing process for high-quality magnetic thin films with low magnetic damping.

Low magnetic damping constant in half-metallic Co2FeAl Heusler alloy thin films grown by molecular beam epitaxy

Half-metallic Co2FeAl Heusler alloy thin films with various thickness were prepared by MBE method and its magnetic and crystalline properties were investigated. At the thickness of 20 nm and above, good magnetic properties and high B2-order parameter was obtained. In addition, magnetic damping constant was evaluated from peak-to-peak linewidth measured by FMR and ultra-low magnetic damping constant below 0.001 was obtained at the film thickness of 30 nm. These results are thanks to the excellent half-metallicity in the Co2FeAl films prepared by MBE.

Anisotropic long-range spin transport in canted antiferromagnetic orthoferrite YFeO3

In antiferromagnets, the efficient transport of spin-waves has until now only been observed in the insulating antiferromagnet hematite, where circularly (or a superposition of pairs of linearly) polarized spin-waves diffuse over long distances. Here, we report long-distance spin-transport in the antiferromagnetic orthoferrite YFeO3, where a different transport mechanism is enabled by the combined presence of the Dzyaloshinskii-Moriya interaction and externally applied fields. The magnon decay length is shown to exceed hundreds of nanometers, in line with resonance measurements that highlight the low magnetic damping. We observe a strong anisotropy in the magnon decay lengths that we can attribute to the role of the magnon group velocity in the transport of spin-waves in antiferromagnets. This unique mode of transport identified in YFeO3 opens up the possibility of a large and technologically relevant class of materials, i.e., canted antiferromagnets, for long-distance spin transport.

Controlling High-Frequency Spin-Wave Dynamics Using Double-Pulse Laser Excitation

Manipulating spin waves is highly required for the development of innovative data transport and processing technologies. Recently, the possibility of triggering high-frequency standing spin waves in magnetic insulators using femtosecond laser pulses was discovered, raising the question about how one can manipulate their dynamics. Here we explore this question by investigating the ultrafast magnetization and spin-wave dynamics induced by double-pulse laser excitation. We demonstrate a suppression or enhancement of the amplitudes of the standing spin waves by precisely tuning the time delay between the two pulses. The results can be understood as the constructive or destructive interference of the spin waves induced by the first and second laser pulses. Our findings open exciting perspectives towards generating single-mode standing spin waves that combine high frequency with large amplitude and low magnetic damping.

Yttrium Iron Garnet-Based Combinatorial Logic and Memory Devices

Yttrium iron garnet Y₃Fe₂(FeO₄)₃ (YIG) has a uniquely low magnetic damping for spin waves, which makes it a perfect material for magnonic devices. Spin waves typically exist in the microwave frequency range and their wavelength can be decreased to the nanoscale. Their dispersion in YIG waveguides depends on the strength and orientation of the bias magnetic field. It may be possible to exploit YIG waveguides as field-controlled filters and delay lines. In this work, we describe combinatorial logic and memory devices to benefit YIG properties. An act of computation in the combinatorial device is associated with finding a route connecting the input and output ports. We present experimental data demonstrating the pathfinding in the active ring circuit with YIG waveguide. The ability to search in parallel through multiple paths is the most appealing property of combinatorial devices. Potentially, they may compete with quantum computers in functional throughput.

Suppressing Magnetic Damping Related to Two-Magnon Scattering in Ultrathin NiFe Films by Interface Engineering

Designing the ferromagnetic/nonmagnetic (FM/NM) heterostructure with desirable low magnetic damping is important for spintronic devices to reduce the critical current density of magnetization switching. For ultrathin FM/NM films, magnetic damping from the two-magnon scattering (TMS) effect is a critical component, and suppressing TMS damping becomes one of the crucial ways to achieve low damping. In this paper, we have demonstrated the depressed linewidth in Ta (1 nm)/NiFe (3 nm)/NM (4 nm)/Ta (1.5 nm) heterostructure with Cu instead of Pt as the NM layer, where the maximal linewidth of ferromagnetic resonance (FMR) decreases from 440 to 190 Oe. And the decrease of TMS damping from 55 to 0 Oe is one of the main reasons for the lower FMR linewidth. The nonzero surface magnetic anisotropy implies that the suppression of interfacial defect scattering causes reduced TMS damping. Meanwhile, a noticeable enhancement of TMS damping from the lack of seed layer may be due to the lattice structure change. Thereby, our findings provide a way toward the design of low-damping spintronic devices.

Room-temperature spin-orbit torque switching in a manganite-based heterostructure

The oxide ferromagnet ${\mathrm{La}}_{0.67}{\mathrm{Sr}}_{0.33}\mathrm{Mn}{\mathrm{O}}_{3}$ (LSMO) possesses low saturation magnetization $({M}_{s})$, a low magnetic damping constant $(\ensuremath{\alpha})$, and high carrier spin polarization, which promise superior functionalities in spintronics devices. For applications, these devices are to be integrated into electronic circuits, which require the control of the magnetization of LSMO by electrical means. However, a reliable electrical switching method remains largely unexplored. Here, we study the current-induced spin-orbit torque (SOT) in an all-oxide $\mathrm{SrIr}{\mathrm{O}}_{3}/\mathrm{LSMO}$ bilayer. We found the magnetization of a 15 nm LSMO can be switched by electrical current, as confirmed from both the electrical transport measurement and the magnetic optical measurement. By taking advantage of the strain-mediated magnetic anisotropy, the magnetic easy axis of LSMO was controlled to be either perpendicular or parallel to the charge current direction such that a type-$y$ or a type-$x$ SOT switching was achieved, respectively. The dampinglike SOT efficiency is characterized to be 0.15 at room temperature according to the harmonic Hall voltage analysis. We also studied the temperature dependences of the SOT effective field and current-induced switching. Our demonstration of the electrical switching of LSMO magnetization at room temperature may stimulate SOT studies in a wide variety of all-oxide systems.

Control of site occupancy by variation of the Zn and Al content in NiZnAl ferrite epitaxial films with low magnetic damping

The structural and magnetic properties of Zn/Al doped nickel ferrite thin films can be adjusted by changing the Zn and Al content. The films are epitaxially grown by reactive magnetron sputtering using a triple cluster system to sputter simultaneously from three different targets. Upon the variation of the Zn content the films remain fully strained with similar structural properties, while the magnetic properties are strongly affected. The saturation magnetization and coercivity as well as resonance position and linewidth from ferromagnetic resonance (FMR) measurements are altered depending on the Zn content in the material. The reason for these changes can be elucidated by investigation of the x-ray magnetic circular dichroism spectra to gain site and valence specific information with elemental specificity. Additionally, from a detailed investigation by broadband FMR a minimum in g-factor and linewidth could be found as a function of film thickness. Furthermore, the results from a variation of the Al content using the same set of measurement techniques is given. Other than for Zn, the variation of Al affects the strain and even more pronounced changes to the magnetic properties are apparent.

Nanoscale-Thick Ni-Based Half-Heusler Alloys with Structural Ordering-Dependent Ultralow Magnetic Damping: Implications for Spintronic Applications

Atomic ordering and its consequence on the crystal structure are fundamental issues in the application of half-metallic Heusler alloys considered as a high spin-polarized electron source. NiMnSb is a promising half-metallic half-Heusler alloy for spintronic devices due to its low magnetic damping, non-centrosymmetric crystal structure, and rich anisotropies. Here, we report a high-quality half-metallic epitaxial nano-scale thick NiMnSb alloy film grown on a Cr/Ag-buffered MgO (001) single crystalline substrate. High temperature deposition is a crucial parameter for crystal growth and magneto-dynamic properties such as damping, anisotropy, magnetization, etc. After investigating the ferromagnetic resonance (FMR) spectroscopy using a time-resolved magneto-optical Kerr (TRMOKE) microscope and calculating the crystal structure using VESTA and the density of states from first-principles calculations, we discuss how the deposition temperature influences the crystal ordering, damping, and magnetization. Ultralow Gilbert damping with high anisotropic field and saturation magnetization were found for the highly ordered C1b structured nano-scale thick NiMnSb film deposited at 573 K. We also found quite nice agreement between theoretical and experimental data of crystal ordering and damping that explains how the ordering affects the magnetic parameter as well as sample quality. Furthermore, the negative anisotropic magnetoresistance ratio implies the robust bulk half-metallicity. Such unique combination of highly ordered half-metallic NiMnSb alloy in the nano-scale regime with ultralow damping can be regarded as an advantage for applications in spintronic devices.

Sub-50 nm wavelength spin waves excited by low-damping Co25Fe75 nanowires

Spin waves are considered as a promising candidate for next-generation logic devices with low power dissipation. Exchange spin waves are particularly attractive for high-speed data processing and scaling down the size of magnonic logic devices. Here, we achieve the excitation of short-wavelength propagating spin waves with wavelengths as short as 45 nm in a 20 nm-thick yttrium iron garnet film covered by 70 nm-wide Co25Fe75 nanowires with low magnetic damping and high saturation magnetization, and the ferromagnetic resonance of Co25Fe75 nanowires is excited by a 200 nm-wide nano-strip line. From our measurements, we extrapolate a group velocity for exchange spin waves of up to 1.9 km/s close to the zero magnetic field (0.5 mT).

Van der Waals Epitaxy of Co10–xZn10–yMnx+y Thin Films: Chemical Composition Engineering and Magnetic Properties

Topologically protected magnetic skyrmions have raised interest for future spintronics applications. One of the main challenges is the synthesis of room temperature skyrmion-hosting materials that are compatible with thin-film technology. We present an approach to produce strain-free epitaxial thin films of Co10–xZn10–yMnx+y using molecular beam epitaxy. Bulk Co10–xZn10–yMnx+y is known to host skyrmions at room temperature for specific composition ratios. Our substrate consists of graphene on oxidized silicon. The van der Waals interactions of the grown material with graphene prevents covalent bonding and corresponding strain. We show how defects in the graphene foster nucleation that results in three different kinds of morphologies: islands, columns, and merged films. Susceptibility measurements suggest a phase transition close to room temperature. We detect up to three spin waves resonances suggesting relatively low magnetic damping. This growth technique opens a new route for the integration of complex alloys and skyrmionic device concepts with silicon electronics.

Magnetoelastic interactions and magnetic damping in Co2Fe0.4Mn0.6Si and Co2FeGa0.5Ge0.5 Heusler alloys thin films for spintronic applications

Co2Fe0.4Mn0.6Si (CFMS) and Co2FeGa0.5Ge0.5 (CFGG) Heusler alloys are among the most promising thin film materials for spintronic devices due to a high spin polarization, low magnetic damping and giant/tunneling magnetoresistance ratios. Despite numerous investigations of Heusler alloys magnetic properties performed up to now, magnetoelastic effects in these materials remain not fully understood; due to quite rare studies of correlations between magnetoelastic and other magnetic properties, such as magnetic dissipation or magnetic anisotropy. In this research we have investigated epitaxial CFMS and CFGG Heusler alloys thin films of thickness in the range of 15–50 nm. We have determined the magnetoelastic tensor components and magnetic damping parameters as a function of the magnetic layer thickness. Magnetic damping measurements revealed the existence of non-Gilbert dissipation related contributions, including two-magnon scattering and spin pumping phenomena. Magnetoelastic constant B11 values and the effective magnetic damping parameter αeff values were found to be in the range of − 6 to 30 × 106 erg/cm3 and between 1 and 12 × 10–3, respectively. The values of saturation magnetostriction λS for CFMS Heusler alloy thin films were also obtained using the strain modulated ferromagnetic resonance technique. The correlation between αeff and B11, depending on magnetic layer thickness was determined based on the performed investigations of the above mentioned magnetic properties.