We investigate magnetization dynamics in a spin-Hall oscillator using a direct current measurement as well as conventional microwave spectrum analysis. When the current applies an anti-damping spin-transfer torque, we observe a change in resistance which we ascribe to the excitation of incoherent exchange magnons. A simple model is developed based on the reduction of the effective saturation magnetization, quantitatively explaining the data. The observed phenomena highlight the importance of exchange magnons on the operation of spin-Hall oscillators.The combination of the spin-Hall effect and the spintransfer torque may be used to compensate the magnetic damping of a ferromagnet, facilitating precession of the macroscopic magnetization by the application of a direct current 1-5 . Such a device, a spin-Hall oscillator, is patterned in a simple current in-plane geometry and contains no tunnel barriers. The ability of the spin-Hall effect to apply a spin-current transverse to the chargecurrent enables the use of conducting magnetic materials as well as low-damping, insulating materials like yttriumiron-garnet (YIG) 5 . This is in contrast to conventional spin-torque nano-oscillators where a spin-polarized current is passed into a conducting ferromagnetic layer 6 . Despite being attractive due to their geometric simplicity and flexibility in choice of magnetic materials, for spin-Hall oscillators to become competitive with conventional spin-torque nano-oscillators, sources of damping such as spin-pumping 7 and multi-magnon scattering via exchange magnons 8,9 should be addressed in order to reduce the linewidth and increase the power generation efficiency. In this Letter we show that the current induced excitation of incoherent exchange magnons can be observed using a direct current measurement. We find a change in the sample resistance which correlates with the reduction of saturation magnetization taken from our spectroscopy measurements, similar to previously reported results 9 . Both phenomena are consistent within a simple model only utilizing the precession cone-angle of the auto-oscillatory exchange magnons.The sample is a Pt(3)/Py(4)/AlO x (1.6) trilayer deposited by d.c. magnetron sputtering onto a MgO substrate. Numbers in parentheses give thicknesses in nanometers. The multilayer is patterned into a 500 nm × 6 µm bar via electron-beam lithography and subsequent Ar ion milling. Adjacent evaporated Cr(5)/Au(50) pads a) current address: Max-Planck-Institut für Quantenoptik, 85748 Garching, Germany b) ajf1006@cam.ac.uk serve as contact pads. When current is applied to this structure, the portion of the current flowing inside the heavy metal (platinum) generates an out-of-plane spincurrent via the spin-Hall effect (SHE). This spin-current exerts a spin-transfer torque (STT) on the magnetization of the ferromagnetic layer (permalloy) 10,11 , which can oppose the magnetic damping, leading to a change in the Gilbert damping parameter α 12,13 :Here, α 0 is the pristine damping parameter, j c,hm is the charge-curren...
We use ferromagnetic resonance to study the current-induced torques in YIG/heavy metal bilayers. YIG samples with thickness varying from 14.8 nm to 80 nm, with Pt or Ta thin film on top, are measured by applying a microwave current into the heavy metals and measuring the longitudinal DC voltage generated by both spin rectification and spin pumping. From a symmetry analysis of the FMR lineshape and its dependence on YIG thickness, we deduce that the Oersted field dominates over spin-transfer torque in driving magnetization dynamics.Introduction -Insulating magnetic materials have recently played an important role in spintronics, since they allow pure spin currents to flow without associated charge transport. Within the family of ferromagnetic insulators, yttrium iron garnet (YIG) holds a special place owing to several favourable properties, including ultra-low damping, high Curie temperature and chemical stability [1][2][3]. By growing an overlayer of heavy metal (HM), such as platinum or tantalum, several important spintronic phenomena have been explored in the YIG/HM bilayer system, including the magnetic proximity effect [4,5], spin pumping [6,7], spin Hall magnetoresistance (SMR) [8,9], spin Seebeck effect [10,11] and so on. Furthermore, the spin Hall effect in HM can convert a charge current into a transverse pure spin current, making it possible to manipulate the ferromagnetic insulator by spin transfer torque (STT). Recently, several groups have reported controlling the damping in YIG by applying a DC charge current in a Pt capping layer [12], by which spin-Hall autooscillation can be realized [13,14]. Replacing the DC current with a microwave current, the electrical signal in Pt can also be transmitted via spin waves in YIG [3]. In order to further explore the application of the YIG/HM system, it is necessary to understand the torque on YIG induced by the charge current in HM.
Spin-dependent transport phenomena due to relativistic spin-orbit coupling and broken space-inversion symmetry are often difficult to interpret microscopically, in particular when occurring at surfaces or interfaces. Here we present a theoretical and experimental study of spin-orbit torque and unidirectional magnetoresistance in a model room-temperature ferromagnet NiMnSb with inversion asymmetry in the bulk of this half-Heusler crystal. Aside from the angular dependence on magnetization, the competition of Rashba-and Dresselhaus-type spin-orbit couplings results in the dependence of these effects on the crystal direction of the applied electric field. The phenomenology that we observe highlights potential inapplicability of commonly considered approaches for interpreting experiments. We point out that, in general, there is no direct link between the current-induced nonequilibrium spin polarization inferred from the measured spin-orbit torque and the unidirectional magnetoresistance. We also emphasize that the unidirectional magnetoresistance has not only longitudinal but also transverse components in the electric field: current indices which complicate its separation from the thermoelectric contributions to the detected signals in common experimental techniques. We use the theoretical results to analyze our measurements of the on-resonance and off-resonance mixing signals in microbar devices fabricated from an epitaxial NiMnSb film along different crystal directions. Based on the analysis we extract an experimental estimate of the unidirectional magnetoresistance in NiMnSb.
Abstract:The inclusion complexes (ICs) between polylactic acid (PLA) and β-cyclodextrin (CD) were prepared by coprecipitation method in this work. The orthogonal experiments were designed to investigate the influence of different factors on the formation of inclusion complexes. The results suggested that the optimum scheme of inclusion compounds could be obtained when the feeding ratio of CD to PLA (wt%) was 20:1, stirring speed was 6 kr/min and the stirring time was 30 min. The structures and properties of the inclusion complexes were characterized by 1 H NMR, FTIR, DSC, FT-Raman, XRD and TGA. The DSC results demonstrated that the crystallization behavior of the inclusion complexes nearly disappeared. It was found that β-CD-PLA inclusion complex had a better thermal stability compared with the neat PLA. The model of the inclusion complexes was proposed on the basis of XRD, 1 H NMR and DSC results.
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