T. J. Silva

Ultra-low magnetic damping of a metallic ferromagnet

Materials with low magnetic damping are important for a range of applications but are typically insulating, which limits their use. Thanks to a unique feature of the band structure, similar levels of damping can now be achieved in a metallic alloy.

High frequency measurements of CoFeHfO thin films

High-frequency measurements of the transverse susceptibility and damping constant of CoFeHfO thin films have been made over a frequency range of 0.1 GHz to 6 GHz as a function of film resistivity, thickness, and temperature. The film resistivity varied from 250 /spl mu//spl Omega/cm to 2100 /spl mu//spl Omega/cm. The films show relatively low damping at high frequencies with the damping constant /spl alpha/ ranging from 0.01 to 0.06. The damping constant increases with film resistivity and, for the highest resistivity films, the damping constant decreases as the thickness increases. The damping constant, induced anisotropy, and film resistivity show weak temperature dependence over a temperature range from 4 K to 300 K. The low damping constant, in conjunction with the high anisotropy, large resistivity, and large spin-dependent-tunneling magnetoresistance, makes this material attractive for several high-frequency magnetic device applications.

Perpendicular Magnetic Anisotropy and Easy Cone State in Ta/Co 60 Fe 20 B 20 /MgO

We used broadband ferromagnetic resonance (FMR) spectroscopy to measure the second- and fourth-order perpendicular magnetic anisotropies in Ta/(t) Co₆₀Fe₂₀B₂₀/MgO layers over a Co₆₀Fe₂₀B₂₀ thickness range of 5.0 nm ≥ t ≥ 0.8 nm. Fort > 1.0 nm, the easy axis is in the plane of the film, but when t <; 1.0 nm, the easy axis is directed perpendicular to the surface. However, the presence of a substantial higher order perpendicular anisotropy results in an easy cone state when t = 1.0 nm. Angular-dependent FMR measurements verify the presence of the easy cone state. Measurement of the spectroscopic g-factor via FMR for both the in-plane and out-of-plane geometries suggests a significant change in electronic and/or physical structure at t ≈ 1.0 nm thickness.

Observation of spin-orbit effects with spin rotation symmetry

The spin–orbit interaction enables interconversion between a charge current and a spin current. It is usually believed that in a nonmagnetic metal (NM) or at a NM/ferromagnetic metal (FM) bilayer interface, the symmetry of spin–orbit effects requires that the spin current, charge current, and spin orientation are all orthogonal to each other. Here we demonstrate the presence of spin–orbit effects near the NM/FM interface that exhibit a very different symmetry, hereafter referred to as spin-rotation symmetry, from the conventional spin Hall effect while the spin polarization is rotating about the magnetization. These results imply that a perpendicularly polarized spin current can be generated with an in-plane charge current simply by use of a FM/NM bilayer with magnetization collinear to the charge current. The ability to generate a spin current with arbitrary polarization using typical magnetic materials will benefit the development of magnetic memories.Converting charge to spin currents using spin–orbit interactions has useful applications in spintronics but symmetry constraints can limit the control over spin polarization. Here the authors demonstrate spin–orbit effects with a different symmetry, which could help generate arbitrary spin polarizations.

Magnetic properties of ultrathin 3d transition-metal binary alloys. I. Spin and orbital moments, anisotropy, and confirmation of Slater-Pauling behavior

The structure and static magnetic properties-saturation magnetization, perpendicular anisotropy, spectroscopic g factor, and orbital magnetization-of thin-film 3d transition metal alloys are determined over the full range of alloy compositions via x-ray diffraction, magnetometry, and ferromagnetic resonance measurements. We determine the interfacial perpendicular magnetic anisotropy by use of samples sets with varying thickness for specific alloy concentrations. The results agreewith prior published data and theoretical predictions. They provide a comprehensive compilation of the magnetic properties of thin-film Ni-x Co1-x, Ni-x Fe1-x, and Co-x Fe1-x alloys that goes well beyond the often-cited Slater-Pauling dependence of magnetic moment on alloy concentration.

Ultrafast Demagnetization Probed at Elemental M-Edges Using Tabletop High-Order Harmonic EUV Light

We use high EUV harmonics generated from tabletop laser to detect the ultrafast demagnetization at M-absorption edge of Fe and Ni. The magnetization is reduced by 60% during the first 250 fs after pump pulses.

Dynamical response on magnetic soft underlayers

In this paper, we have made the first direct dynamical measurements of both exchange coupled and non-exchange coupled magnetic soft underlayer (SUL) materials suitable for perpendicular recording. We have found that damping increased by a factor of 2 to 3 for the exchange coupled sample compared to the non-exchange coupled samples. The exchange coupled sample consisted were composed of 50 nm of FeCo with three different 2.5 nm thick seedlayers:Cu, NiFe, and Ru.