We determined the Gilbert damping constants of Fe-Co-Ni and Co-Fe-B alloys with various compositions and half-metallic Co 2 MnAl Heusler alloy films prepared by magnetron sputtering. The ferromagnetic resonance (FMR) technique was used to determine the damping constants of the prepared films. The out-of-plane angular dependences of the resonance field (H R ) and line width (ÁH pp ) of FMR spectra were measured and fitted using the Landau-Lifshitz-Gilbert (LLG) equation. The experimental results fitted well, considering the inhomogeneities of the films in the fitting. The damping constants of the metallic films were much larger than those of bulk ferrimagnetic insulators and were roughly proportional to ðg À 2Þ 2 , where g is the Lande g factor. We discuss the origin of magnetic damping, considering spin-orbit and s-d interactions.

We investigated the spin-torque diode effect in submicron-scale Co60Fe20B20∕MgO∕(CoxFe1−x)80B20 (0⩽x⩽0.9) magnetic tunnel junctions (MTJs) under perpendicular magnetic fields Hext up to 10kOe. A single peak was clearly observed in every spin-torque diode spectrum and the dependence of resonant frequency fres on Hext was well explained by using Kittel’s formula. It was found that effective demagnetizing fields in the perpendicular-to-plane direction of the Fe-rich CoFeB free layers obtained from the spectra were considerably smaller than those expected from the magnetizations of the free layers. This suggested that the Fe-rich CoFeB free layers exhibited a perpendicular magnetic anisotropy, which agreed well with the reduced switching current density in the MTJs.

Spin pumping in nonmagnetic/ferromagnetic metal multilayers is studied both theoretically and experimentally. We show that the line widths of the ferromagnetic resonance (FMR) spectrum depend on the thickness of the ferromagnetic metal layers, which must not be in resonance with the oscillating magnetic field. We also show that the penetration depths of the transverse spin current in ferromagnetic metals can be determined by analyzing the line widths of their FMR spectra. The obtained penetration depths in NiFe, CoFe and CoFeB were 3.7 [nm], 2.5 [nm] and 12.0 [nm], respectively.PACS numbers: 72.25. Mk, 75.70.Cn, 76.50.+g, 76.60.Es The field of current-driven magnetization dynamics (CDMD) has drawn enormous attention because of its potential applications to non-volatile magnetic random access memory and microwave devices. CDMD is also important from a scientific point of view since it provides much information about non-equilibrium dynamics of the magnetization and physics of spin transport and spin relaxation. The concept of CDMD was first proposed by Slonczewski [1] and independently by Berger [2] in 1996. In the last decade much effort has been devoted to studying the physics and applications of CDMD both theoretically and experimentally [3,4].One of the most important quantities in CDMD is the penetration depth of the transverse spin current λ t , over which spin transfer torque is exerted for the magnetization of the free layer. However, there is a controversial issue regarding the penetration depth of the transverse spin current. One argument is based on the ballistic theory of electron transport, and its λ t = π/|k ↑ F − k ↓ F |, which is on the order of the lattice constant in conventional ferromagnets such as Fe, Co, Ni, and their alloys [5,6]. The other argument is based on the Boltzmann theory of electron transport, and its λ t is on the order of a few nm [7]. Urazhdin et al. analyzed the CPP-GMR of noncollinear magnetic multilayers using the extended twoseries-resistance model and concluded that λ t =0.8 [nm] for permalloy [8]. On the other hand, Chen et al. analyzed the critical current of the CDMD in the Co/Cu/Co trilayer system and concluded that λ t =3.0 [nm] for Co [9].The inverse process of CDMD is spin pumping, where spin current is generated by precession of magnetization in the ferromagnetic layer [10]. Enhancement of the Gilbert damping constant due to spin pumping has been extensively studied, and spin diffusion lengths, i.e., penetration depths of spin current in nonmagnetic metals, have been obtained by analyzing the dependence of the enhancement of the Gilbert damping constant on the thickness of the nonmagnetic metal layer. In spin FIG. 1: Schematic illustration of a nonmagnetic/ferromagnetic metal five-layer system. The magnetization of the F1 layer (m1) precesses around the z-axis with angle θ. The magnetization of the F2 layer (m2) is fixed with the z-axis. The precession of the magnetization in the F1 layer pumps the spin current I pump s . The pumped spin current creates spin a...

We prepared MgO-based magnetic tunnel junctions having a CoFeB/Ru/CoFeB synthetic free layer in which magnetizations of the CoFeB layers were ferromagnetically coupled (F-coupled Sy) or antiferromagnetically coupled (AF-coupled Sy). We studied spin-transfer switchings to evaluate their thermal stability (Δ0=KV/kBT) and intrinsic switching current density (JC0). Although the free layers of two types showed nearly equal JC0, the Δ0 of F-coupled Sy was observed to be twice that of AF-coupled Sy. This difference is attributable to the shape magnetic anisotropy of the free-layer cells. Results show that F-coupled Sy is superior to AF-coupled Sy for memory applications.

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