Showing papers by "Thomas J. Silva published in 2000"
TL;DR: In this paper, the authors demonstrate a method of eliminating overshoot and ringing in magnetization dynamics when the system bandwidth includes the intrinsic ferromagnetic resonance (FMR) and employ staggered step excitation for the cancellation of FMR oscillations while maximizing the magnetization response.
Abstract: We demonstrate a method of eliminating overshoot and ringing in magnetization dynamics when the system bandwidth includes the intrinsic ferromagnetic resonance (FMR) The method employs staggered step excitation for the cancellation of FMR oscillations while maximizing the risetime of the magnetization response The second-harmonic magneto-optic Kerr effect is used to measure the magnetic response at a localized spot on the sample The measured response is adequately modeled with the Landau–Lifshitz–Gilbert differential equation We explain the observed behavior in terms of destructive interference
53 citations
TL;DR: In this paper, the high frequency characteristics of 100 nm FeTaN films have been studied by using both time-resolved inductive techniques and frequencyresolved permeability measurements.
Abstract: The high frequency characteristics of 100 nm FeTaN films have been studied by using both time-resolved inductive techniques and frequency-resolved permeability measurements. Experiments performed as a function of longitudinal bias fields from 120 to 2400 A/m (1.5–30 Oe) showed precessional frequencies from 1.3 to 2.5 GHz, initial permeabilities from 1600 to 500, and damping constants α=0.013 to 0.0045. It is illustrated that the magnetization precessional data obtained from the time-resolved inductive technique can be Fourier transformed to the frequency domain to give the real and imaginary components of a permeability spectrum; this spectrum compares well with data obtained from frequency-resolved permeability measurements. It is also demonstrated that accurate values of the damping constant α can only be determined from permeameters whose bandwidth is two to three times the ferromagnetic resonance frequency of the material to be measured.
42 citations
TL;DR: In this paper, the authors used a wide-field Kerr microscope to measure magnetization reversal in high coercivity thin film media that were subjected to nanosecond field pulses, and they found that after a step change in H, the magnetization initially relaxes exponentially with a time constant of 5 ns, and then relaxes logarithmically.
Abstract: We used a wide-field Kerr microscope to measure magnetization reversal in high coercivity thin film media that were subjected to nanosecond field pulses. Coplanar waveguides were used as a field source. Two different samples of CoCr/sub 10/Ta/sub 4/ were measured. Sample A had a coercivity of 83 kA/m and sample B had a coercivity of 167 kA/m. For sample A, we find that after a step change in H, the magnetization initially relaxes exponentially with a time constant of 5 ns, and then relaxes logarithmically. We interpret this result as indicating a transition from dynamic reversal to thermal relaxation. In higher fields, the exponential relaxation time decreases according to /spl tau/=S/sub w//(H-H/sub 0/), where S/sub w/=29.7 /spl mu/s/spl middot/A/spl middot/m/sup -1/ (373 ns/spl middot/Oe). For sample B, only logarithmic relaxation is observed, implying that the dynamic magnetization response time is subnanosecond. We observe correlated regions of reversed magnetization in our Kerr images of sample A with a typical correlation length of 1 /spl mu/m along the applied field direction. We propose a microscopic model of nucleation and growth of reversed regions by analogy to viscous domain wall motion.
23 citations
TL;DR: In this article, a significant modification of an existing experimental technique based on the second-harmonic magneto-optical Kerr effect (SH-MOKE) is introduced, which permits simultaneous vectorial measurement of the in-plane magnetization components.
Abstract: A significant modification of an existing experimental technique based on the second-harmonic magneto-optical Kerr effect (SH-MOKE) is introduced. With a p-polarized pumping optical wave incident upon a magnetic film, the transverse component of magnetization causes a change in the second-harmonic generation efficiency of the material and the longitudinal component of the magnetization produces a change in the polarization rotation and/or ellipticity of the second-harmonic signal. This permits simultaneous vectorial measurement of the in-plane magnetization components. Examples of measured hysteresis loops from 50 nm thick permalloy films and procedures for SH-MOKE signal calibration are presented.
13 citations
01 Sep 2000
TL;DR: In this article, large angle rotations were studied in Permalloy thin films and spin valve devices and it was shown that edge effects or inhomogeneities strongly influence the magnetization behavior under certain initial conditions.
Abstract: Large angle rotations were studied in Permalloy thin films and spin valve devices. It is shown that edge effects or inhomogeneities strongly influence the magnetization behavior under certain initial conditions. Complicated intermediate states can form which significantly increase the magnetization response time.
13 citations
TL;DR: In this article, the demagnetizing field across bit transitions in longitudinal recording media is measured quantitatively as a function of linear density using a quasi static write/read tester.
Abstract: The demagnetizing field across bit transitions in longitudinal recording media is measured quantitatively as a function of linear density using a quasi static write/read tester. Bit transitions with varying linear densities in the range 500–6000 flux changes per mm are recorded on CoCr10Ta4 media films. The media are deposited onto a coplanar waveguide structure, which is used to generate reversal field pulses of well-defined amplitude and 10 ns width to minimize thermally activated processes. The demagnetizing field is extracted from the measured reversal field, which is the sum of the external waveguide field and the internal, density-dependent demagnetizing field. The experimental results are qualitatively consistent with those predicted by a simple magnetostatic model that assumes finite transition widths.
6 citations
09 Apr 2000
2 citations
09 Apr 2000
TL;DR: A low-cost inductive current probe designed for integration into a disk drive trace suspension assembly is described in this paper, where the main consideration for this design was to use the same materials currently found in trace suspension assemblies, and thus reducing costs, while at the same time providing a drive characterization tool capable of measuring 100 ps head field rise times.
Abstract: A low-cost, inductive current probe designed for integration into a disk drive trace suspension assembly is described. The main consideration for this design was to use the same materials currently found in trace suspension assemblies, and thus reducing costs, while at the same time providing a drive characterization tool capable of measuring 100 ps head field rise times. The inductive current probe consists of a pair of differential copper conductors fabricated adjacent to the write driver interconnects and magnetically coupled via a Ni-Fe thin film placed on top of these conductors. The differential conductor pair is connected to a high-speed sampling oscilloscope to measure the speed of the write current pulse and thus infer the write head field rise time. Data are shown for high-speed pulses generated with rise times of less than 100 ps.