Michael L. Schneider

Ferromagnetic resonance linewidth in metallic thin films: Comparison of measurement methods

Stripline (SL), vector network analyzer (VNA), and pulsed inductive microwave magnetometer (PIMM) techniques were used to measure the ferromagnetic resonance (FMR) linewidth for a series of Permalloy films with thicknesses of 50 and 100nm. The SL-FMR measurements were made for fixed frequencies from 1.5to5.5GHz. The VNA-FMR and PIMM measurements were made for fixed in-plane fields from 1.6to8kA∕m (20–100Oe). The results provide a confirmation, lacking until now, that the linewidths measured by these three methods are consistent and compatible. In the field format, the linewidths are a linear function of frequency, with a slope that corresponds to a nominal Landau-Lifshitz phenomenological damping parameter α value of 0.007 and zero frequency intercepts in the 160–320A∕m (2–4Oe) range. In the frequency format, the corresponding linewidth versus frequency response shows a weak upward curvature at the lowest measurement frequencies and a leveling off at high frequencies.

Dependence of magnetization dynamics on magnetostriction in NiFe alloys

We present a quantitative, systematic study of the effect of magnetostriction on the dynamical properties in NiFe alloys. Both the ferromagnetic resonance frequency and the damping times are correlated to the magnetostriction. In addition, we find that the Gilbert damping parameter varies by more than 100% over the range of Ni percentage tested (61.9%–86.7%).

Enhanced ferromagnetic damping in Permalloy∕Cu bilayers

We have investigated the enhancement of ferromagnetic damping for thin Permalloy (Ni80Fe20) films grown with Cu capping layers of variable thickness (5–1000 nm). The measurements were performed with a pulsed inductive microwave magnetometer in the frequency range between 2.3 and 2.7 GHz. The damping was enhanced if the Cu layers were thicker than the spin-diffusion length of ls≈250nm. For example, the damping was enhanced by 30% for a Permalloy (3nm)∕Cu (1000 nm) bilayer relative to the damping for Permalloy with a 5-nm-thick Cu capping layer. Existing theory for spin pumping from the Permalloy layer into the Cu layer was used to model the additional contribution to damping for these bilayer systems. Additional experiments on Permalloy (5nm)∕Cu(xnm)∕Ta (5 nm) provided indirect evidence for spin accumulation inside the Cu layer.

Large-angle magnetization dynamics measured by time-resolved ferromagnetic resonance

A time-resolved ferromagnetic resonance technique was used to investigate the nonlinear magnetization dynamics of a

Dynamic anisotropy of thin Permalloy films measured by use of angle-resolved pulsed inductive microwave magnetometry

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Gyromagnetic damping and the role of spin-wave generation in pulsed inductive microwave magnetometry

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Spin dynamics and damping in nanomagnets measured directly by frequency-resolved magneto-optic Kerr effecta)

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Ultralow power artificial synapses using nanotextured magnetic Josephson junctions

film in response to a sequence of large-amplitude field pulses. The magnetic field pulse sequence was set at a repetition rate equal to the magnetic systems resonance frequency. Both inductive and optical techniques were used to observe the resultant magnetization dynamics. We compared data obtained by this technique with conventional pulsed inductive microwave magnetometry. The results for damping and frequency response obtained by these two different methods coincide in the limit of a small-angle excitation. However, when applying large-amplitude field pulses, there was a substantial increase in the apparent damping. Analysis of vector-resolved magnetic second-harmonic generation data indicate that the increase in damping is correlated with a decrease in the spatial homogeneity of the magnetization dynamics. This suggests that unstable spin wave generation occurs in the limit of large-amplitude dynamics.

Evolution of the density of states at the Fermi level ofBi2−yPbySr2−xLaxCuO6+δandBi2Sr2−xLaxCuO6+δcuprates with hole doping

In this study, angle-resolved pulsed inductive microwave magnetometry is used to investigate the symmetry of the dynamic anisotropy of thin Permalloy films. We measured the dynamic anisotropy field as a function of angle between the easy axis and the applied bias field. We found that, in addition to the expected uniaxial anisotropy, there is a rotatable component of anisotropy. This component of the anisotropy is present only during the dynamics measurements and is attributed to surface effects in the thin films. However, the native oxide layer is not the cause of the rotatable anisotropy components in these films.

Experimental determination of the inhomogeneous contribution to linewidth in Permalloy films using a time-resolved magneto-optic Kerr effect microprobe

The dependence of the magnetodynamic response of thin permalloy films was measured with a pulsed inductive microwave magnetometer as a function of varying width of the coplanar waveguide center conductor (220to990μm), frequency (0.6to2GHz) and film thickness (25to93nm) to ascertain the role of magnetostatic spin-wave generation in the low-frequency enhancement of the measured decay rate. A component of the decay rate depends on δw, the ratio of film thickness to center conductor width as theoretically predicted. However, there is an anomalous contribution to the frequency dependence of the decay rate exists that cannot be attributed to the generation of spin-waves.