| 1. |
- Sun, Li, et al.
(författare)
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Anomalously large ferromagnetic resonance linewidth in the Gd/Cr/Fe film plane
- 2018
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 451, s. 480-486
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Tidskriftsartikel (refereegranskat)abstract
- As an important parameter for characterizing the magnetization dynamics, Gilbert damping constant a in a thin film or a multilayer is generally extracted from the linear fitting of the frequency-dependence of the ferromagnetic resonance linewidth, sometimes accompanied with a tiny deviation of the linewidth to a smaller value at the low-frequency or high-frequency region due to the two-magnon scattering with an in-plane-field configuration, in which an in-plane magnetic field H perpendicular to a microwave field h was applied in film plane during measurement. In contrast, here we report, in ultrathin Gd/Cr/Fe multilayers, an anomalously large linewidth in the film plane at the low-frequency region. For the first time, we have successfully extracted the Gilbert damping constant from perfect theoretical fitting to the experimental data, by considering the effective direction of the magnetization around in precession staying out of the film plane when the in-pane H at which the precession starts is below the saturation field. This magnetization deviation from the film plane is found to have an obvious contribution to the enhanced linewidth caused by two magnon scattering, while slightly reduce the intrinsic linewidth. Under the same resonance frequency, the deviation angle reaches the maximum values at t(Cr) = 1.0 nm while decreases when t(Cr) increases to 1.5 nm, which coincides with the trend of the surface perpendicular anisotropy constant K-perpendicular to. A reduced intrinsic damping constant alpha is obtained as the introduction of Gd layer and Cr layer as a result of the competition between the spin pumping effect and the interfacial effects at the Fe/Gd and Fe/Cr interfaces. While the decreasing alpha for film with Cr layer thickness increasing to 1.5 nm might means the contribution of the electron density of states at the Fermi energy n(E-F). This study offers an effective way to accurately obtain the intrinsic damping constant of spintronic materials/devices, which is essential for broad applications in spintronics.
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| 2. |
- Yin, Yuli, et al.
(författare)
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Ferromagnetic and Spin-Wave Resonance on Heavy-Metal-Doped Permalloy Films : Temperature Effects
- 2017
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Ingår i: IEEE Magnetics Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1949-307X .- 1949-3088. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Broadband ferromagnetic resonance (FMR)spectroscopy is used to study the temperature (T)and dopantconcentration dependence of the magnetodynamic properties of Permalloy (Py = Ni80Fe20)and Py-100- M-x(x) films, where the dopant M = Pt, Au, and Ag. The saturation magnetization (MS)and Gilbert damping constant (a)are determined from the uniform FMR mode, while the spin wave stiffness (D)is extracted using the first perpendicular standing spinwave mode. The temperature dependence of D is best described by a T (2) law, which suggests a noticeable effect of the itinerant character of the electrons. The spin wave stiffness is also estimated using Bloch's law and the two methods are compared. The results strongly imply that not only spin wave and Stoner excitations, but also other mechanisms contribute to the reduction of MS. The damping increases with T for all samples, but the enhancement is most pronounced for Py doped with 30 at.% Au.
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| 3. |
- Yin, Yuli, et al.
(författare)
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Tunable permalloy-based films for magnonic devices
- 2015
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Ingår i: Physical Review B. - 1098-0121 .- 1550-235X. ; 92:2
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Tidskriftsartikel (refereegranskat)abstract
- Using both broadband ferromagnetic resonance (FMR) spectroscopy and ab initio calculations, we study the magnetodynamic properties of permalloy (Py, Ni80Fe20) and Py100-x M-x films with M as platinum (Pt), gold (Au), or silver (Ag). From the uniform FMR mode, we extract the saturation magnetization (M-S), damping (alpha), and inhomogeneous broadening (Delta H-0); from the first perpendicular standing spin-wave (PSSW) mode, we extract the exchange stiffness (A). M-S and A are found to decrease with increasing alloying, most strongly for Au and less so for Pt. On the other hand, alpha increases rapidly with both Pt and Au content, while being virtually independent of Ag content. The physical origins of the observed trends in alpha, M-S, and A are analyzed and explained using density functional theory calculations in the coherent potential approximation. The calculated trends quantitatively agree with the experimental observations. The drastically different impacts of Pt, Au, and Ag on the various fundamental magnetodynamic properties will allow for significant design freedom, where different properties can be varied independently of others through careful combinations of the Pt, Au, and Ag contents of Py100-x M-x films. By empirical approximations of each property's concentration dependence, we can dial in any desired combination of magnetodynamic properties within this parameter space. As a proof-of-principle demonstration we design a set of Py100-x-yPtxAgy films, where the saturation magnetization stays constant throughout the set and the damping can be tuned by a factor of 4.
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