Spin Hall effects intermix spin and charge currents even in nonmagnetic materials and, therefore, ultimately may allow the use of spin transport without the need for ferromagnets. We show how spin Hall effects can be quantified by integrating Ni{80}Fe{20}|normal metal (N) bilayers into a coplanar waveguide. A dc spin current in N can be generated by spin pumping in a controllable way by ferromagnetic resonance. The transverse dc voltage detected along the Ni{80}Fe{20}|N has contributions from both the anisotropic magnetoresistance and the spin Hall effect, which can be distinguished by their symmetries. We developed a theory that accounts for both. In this way, we determine the spin Hall angle quantitatively for Pt, Au, and Mo. This approach can readily be adapted to any conducting material with even very small spin Hall angles.

Spin pumping is a mechanism that generates spin currents from ferromagnetic resonance over macroscopic interfacial areas, thereby enabling sensitive detection of the inverse spin Hall effect that transforms spin into charge currents in nonmagnetic conductors. Here we study the spin-pumping-induced voltages due to the inverse spin Hall effect in permalloy/normal metal bilayers integrated into coplanar waveguides for different normal metals and as a function of angle of the applied magnetic field direction, as well as microwave frequency and power. We find good agreement between experimental data and a theoretical model that includes contributions from anisotropic magnetoresistance and inverse spin Hall effect. The analysis provides consistent results over a wide range of experimental conditions as long as the precise magnetization trajectory is taken into account. The spin Hall angles for Pt, Pd, Au, and Mo were determined with high precision to be 0.013Ϯ 0.002, 0.0064Ϯ 0.001, 0.0035Ϯ 0.0003, and −0.0005Ϯ 0.0001, respectively.

Highly chemically ordered L1 0 FePtX-Y nano-granular films with high perpendicular magnetic anisotropy are key media approaches for future heat-assisted magnetic recording (HAMR). They are sputtered at elevated temperature on glass disks coated with adhesion, heat sink, and texturing layers. Adding X ¼ Ag reduces the required deposition temperature and X ¼ Cu lowers the Curie temperature. Current seed layers are NiTa for adhesion and heat sink and well-oriented MgO (002) layers for highly textured FePtX(002) grains surrounded by Y ¼ carbon and/or other segregants. Magnetic anisotropies larger than 4.5 Â 10 7 erg cm À3 and coercivities beyond 5 Tesla have been achieved. The combination of thermal conductivity and Curie temperature determines the required laser power during recording. Key goals are to optimize media, heads, head-disk-spacing, and read-back channels to extend the areal density to 1.5-5 Tb in À2

Magnetization dynamics in alloys of ferrimagnetic CoGd have been studied in the vicinity of the magnetization and angular momentum compensation point as a function of alloy composition and temperature. In agreement with standard mean-field treatments of the dynamics of the total magnetization we observe an increase of the precessional frequency and the effective damping parameter near the angular momentum compensation point. We demonstrate the consistency of the magnetization dynamics extracted from frequency domain methods such as ferromagnetic resonance and time resolved laser pump-probe measurements. DOI: 10.1103/PhysRevB.74.134404 PACS number͑s͒: 75.40.Gb, 75.50.Gg, 76.50.ϩg Transition metal ͑TM͒ rare earth ͑RE͒ ferrimagnets are ideal canonical systems to probe magnetization dynamics. Typically, TM-RE alloys are nearly amorphous materials. The TM sublattice is antiferromagnetically ͑AF͒ coupled to the RE sublattice. When the coupling is strong, as, e.g., in CoGd, there are two transition temperatures, the magnetization compensation temperature T M where M Gd = M Co , and the angular momentum compensation temperature T L , where M Gd / ␥ Gd = M Co / ␥ Gd , and ␥ is the gyromagnetic ratio. These temperatures are sensitive functions of the relative concentration. At the magnetic compensation temperature, applied magnetic fields cannot couple to the magnetization to alter its energy since M Gd − M Co = M eff = 0. Angular momentum is quenched at the angular momentum compensation point, where the AF coupled sublattices gyrate 180°out of phase about the magnetic field. Studying the dynamics in ferrimagnetic systems are complicated by these tightly coupled AF sublattices. As T L is approached from low temperatures, the phenomenological mean-field damping parameter ␣ eff which governs how fast the system as a whole dissipates energy increases quickly, and the gyromagnetic frequency changes sign as the angular momentum of the dominant sublattice changes from Gd to Co. An ideal ferrimagnet should dissipate angular momentum instantaneously at T L .1,2 CoGd was chosen for this study because T M and T L are very close to each other, and the intrinsic orbital moment of Gd is essentially zero, thereby eliminating additional loss channels due to spin-orbit coupling. 3 We compare experimental results obtained by a frequency domain method used to study the dynamics of the total magnetization of M eff -namely, ferromagnetic resonance ͑FMR͒-to time domain ultrafast laser pump/probe experiments.The most straight forward method to excite magnetization dynamics uses strong magnetic field pulses that couple directly to the magnetization ͑spin͒.4,5 These field pulses are typically produced by external sources. However, these methods cannot excite the magnetization at the magnetization compensation point in a ferrimagnet since there is no net magnetic moment one can couple to. Another method to excite spin-systems employs ultrashort laser pulses that alter the magnetic system by heating across a critical temperature ͑Curie, Néel, ...

Heat-assisted magnetic recording (HAMR) media status, requirements, and challenges to extend the areal density (AD) of magnetic hard disk drives beyond current records of around 1.4 Tb/in.2 are updated. The structural properties of granular high anisotropy chemically ordered L10 FePtX-Y HAMR media by now are similar to perpendicular CoCrPt-based magnetic recording media. Reasonable average grain diameter ⟨D⟩ = 8–10 nm and distributions σD/D ∼ 18% are possible despite elevated growth temperatures TG = 650–670 °C. A 2× reduction of ⟨D⟩ down to 4–5 nm and lowering σD/D < 10%–15% are ongoing efforts to increase AD to ∼4 Tb/in.2. X = Cu ∼ 10 at. % reduces the Curie temperature TC by ∼100 K below TC,bulk = 750 K, thereby lowering the write head heat energy requirement. Multiple FePtX-Y granular layers with Y = 30–35 vol. % grain-to-grain segregants like carbides, oxides, and/or nitrides are used to fully exchange decouple the grains and achieve cylindrical shape. FePt is typically grown on fcc MgO (100) seedlayers to form well oriented FePt (002). A FePt lattice parameter ratio c/a ∼0.96 and high chemical order S > 0.90 result in magnetic anisotropy KU ∼ 4.5 × 107 erg/cm3, and only 25% below the FePt single crystal value KU = 6.6 × 107 erg/cm3 has been achieved in 7–8 nm diameter grains. Switching field distributions depend on anisotropy field (HK) distributions, which are currently of the order of ΔHK/HK ∼ 10% (ΔHK ∼ 10–12 kOe, HK ∼ 10–11 T) at room temperature. High thermal conductivity heat sink layers, including Ag, Au, Cu, and Cr, are used to optimize the cooling rate and maximize the down- and cross-track thermal gradient, which determines the achievable track density.