Numerical Analysis of Spin-Valve Heads with Overlapping Leads

In this article we present a quantitative micromagnetic modeling analysis of thermally activated magnetic noise in spin valves heads at deep submicron track widths. It is found that, for these spin valve heads, the thermal magnetic noise is at a magnitude that is comparable to that of the head’s Johnson noise. Reducing the sensor track width by keeping the same aspect ratio and film layer thickness will not necessarily yield an increase of thermal magnetic noise, which is attributed to the accompanying increase of the demagnetization field within the sensing layer. However, both the magnitude of noise and the noise spectra are strong functions of the sensor stripe height. An excessive stripe height will yield significantly higher thermal magnetic noise.

A novel scheme essentially eliminates side-reading while maintaining on-track magnetic sensitivity for spin-valve read heads. By directly patterning a magnetic layer that is antiparallelly coupled with the free layer beyond the track edges, the magnetic torque generated by signal field in the wing regions of the free layer can be counterbalanced by the torque generated by the patterned layer via the antiparallel coupling. The magnetic read width of the sensor becomes essentially the same as the physical track width for track widths as low as 50 nm. With this scheme, the on-track magnetic sensitivity exhibits virtually no reduction as track width reduces from 200 to 50 nm. In addition, the scheme enables recessing the contact leads from the track edges to reduce shield-to-shield widening at the track edges.

In this work, the performance of an antisymmetric dual magnetoresistive (A-DMR) head, having a track-width of W/sub t/=2 /spl mu/m, a stripe height of h=2 /spl mu/m and a gap length of 80 nm, is presented and compared to theory. A thin film inductive head that incorporates high magnetization FeAlN poles, with a gap length of 0.25 /spl mu/m, was used to record thin film disk media with an areal magnetic moment of 0.5 memu/cm/sup 2/ and a coercivity of 3 kOe. The A-DMR roll-off and spectral curves that are fit in amplitude and shape with a 2-D analytical curve, indicated D50=190 kfci. The theoretical curves fit the experimental data with two fitting parameters, the spacing parameter of the spacing loss term and a parameter /spl zeta/=/spl zeta/ (W/sub t//h) that can be calculated with a 3-D micromagnetic model. The cross-track profile, off-track response and adjacent track interference are analyzed in the time domain and compared with previously reported theoretical results, where in this case the write head track-width is 2.5 /spl mu/m. The head showed some adjacent track interference and pulse amplitude asymmetry at lower linear densities, mainly due to a lower magnetic transverse bias level of one of the sensor layers. In spite of the good linear resolution of these heads, they offer limited sensitivity in comparison to spin valve heads.

The anisotropic magnetoresistance (AMR) of nickel and cobalt bars of 1 μm length, 35 nm thickness, and width varying from 50 to 500 nm is studied. As the bar width is reduced from 500 to 50 nm, longitudinal MR change decreases from 0.8% to 0.2% and transverse MR change increases from 1.3% to 1.8% for the Ni bars; longitudinal MR change is zero and transverse MR change is constant at 1.6% for the Co bars. The zero longitudinal MR is attributed to a single-domain magnetization. The AMR value indicates that the electron scattering from bar edges has little effect on AMR even in a 50 nm width. Furthermore, strong, repeatable Barkhausen noise is observed in the Co bars with a width larger than 200 nm, which can be explained by a micromagnetic model.

Numerical evaluation for the effective slab width of continuous composite beams

The in-stack stabilization of unshielded and shielded magnetic tunnel junction (MTJ) sensors have been studied experimentally by quasi-static and recording tests as well as theoretically by micromagnetic modeling. Results showed the viability of in-stack stabilization over a range of design and material conditions. Performance tradeoff studies and design optimization results led to the fabrication of MTJ read heads with good magnetic stability and high readback sensitivity.

For the MR strips stabilized by the permanent magnet films, we numerically analyze the effects of the leakage field of the permanent magnet films on the bias angle in the MR films. Using the magnet films as the domain control films, magnetization rotation in the MR films at the track edges is suppressed by their leakage fields and will in turn decrease the effective track width. The decrease effective track width is thought to be due to the large leakage field especially at the track edges, so we examined some cases of decreasing the leakage field at track edges. Among the cases, the effective track width was most effectively enlarged when the distance between the magnet films was widened compared with the spacing of the leads. >

On the parametric sensitivity of heat generation by resonant microwave fields in process fluids

Local temperature of a nanoscale volume is precisely determined by tip-enhanced terahertz Raman spectroscopy in the low temperature range of several tens of degrees. Heat generated by the tip-enhanced electric field is directly transferred to single-walled carbon nanotubes by heat conduction and radiation at the nanoscale. This heating modulates the intensity ratio of anti-Stokes/Stokes Raman scattering of the radial breathing mode of the carbon nanotube based on the Boltzmann distribution at elevated temperatures. Owing to the low-energy feature of the radial breathing mode, the local temperature of the probing volume has been successfully extracted with high sensitivity. The dependence of the temperature rise underneath the tip apex on the incident power coincides with the analytical results calculated by finite element method based on the tip enhancement effect and the consequent steady-state temperature via Joule heat generation. The results show that the local temperature at the nanoscale can be controlled in the low temperature range simply by the incident laser power while exhibiting a sufficiently high tip enhancement effect as an analytical tool for thermally sensitive materials (e.g., proteins, DNA). Graphical Abstract Tip-enhanced THz Raman spectroscopy detects the low frequency Raman mode both in Stokes and anti-Stokes shifts, which precisely reflects the local temperature of the sample volume.

In present study, to investigate the thermal effects of the rechargeable neuromodulation implants (an implant and antenna together) in the body, a numerical analysis is performed by using commercial software ANSYS. Since it is well established that both the antenna and the implant generate heat, both of these heat sources may increase the tissue temperature in the subcutaneous zone and may also increase the temperature in the deeper tissue. Therefore, the sizes and heat generation amounts of the implant-antenna system gain great importance and a parametric evaluation that shows the effects of the design parameters on the temperature becomes necessary. For this aim, an optimization study is performed. The runs of the numerical simulations are determined by well-known design analysis method, namely Taguchi and the parametric evaluation of the study is carried out by Analysis of Variance (ANOVA) method. The design parameters considered are; (i) heat generated by the antenna q a (50, 52 and 54 W/m2), (ii) heat generated by the implant q i (30 and 35 W/m2), (iii) thickness of the implant t i (9, 11, and 13 mm) and finally (iv) the radius of the antenna R a (31, 35, 39 mm). The results showed that higher antenna radii result in higher temperatures in the tissue, whilst the least effective design parameter on the temperature is the heat generation of the implant.

Narrow track recording in a double-layer perpendicular film medium is studied via micromagnetic modeling. A 3-D probe head field with a track width W=1.5 mu m is used for recording simulations. Recordings of multiple consecutive transitions are simulated. Edge transition patterns and edge overwrite properties are characterized. Simulated transition magnetization pattern at track edges turns towards to the head motion direction and extends to the next transition front. Edge overwrite is studied by simulating recording of a new track over a previously recorded track. It is found that the edges of the new track exhibit no separations with the overwritten track and the intertrack edge of newly recorded transitions is strongly modified by the previously written transitions.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Anesthesia Literature Review

The effects of the pole-tip geometry at the air-bearing surface on perpendicular recording at a skew angle are examined through modeling and spin-stand test data. Head fields generated by the finite element method were used to record transitions within our previously described micromagnetic recording model. Write-field contours for a variety of square, rectangular, and trapezoidal pole shapes were evaluated to determine the impact of geometry on field contours. Comparing results for recorded track width, transition width, and media signal to noise ratio at 0° and 15° skew demonstrate the benefits of trapezoidal and reduced aspect-ratio pole shapes. Consistency between these modeled results and test data is demonstrated.

The internal heating rates from the capture and scatter of neutrons and primary gamma radiation represent one of the most significant loadings acting on the reactor pressure vessel internal structures. The nuclear heating effects on the internal structures are mitigated by the flow of the primary coolant removing heat energy from these structures. This paper discusses the use of transfer functions to predict the time-dependent thermal stresses in the lower core plate of reactor vessel internals. Numerous stress analysis applications have employed the transfer function approach to obtain thermal stresses from fluid transients in reactor pressure vessel and piping locations. These solutions have been utilized in both design analysis applications and in stress and fatigue monitoring roles for evaluation of pressure vessels subjected to fluid transients and mechanical loads such as pressure and piping loads. This paper presents a further extension of the technology to address heat generation loads. The evaluation of stress and fatigue produced in a reactor vessel internals lower core plate due to multiple loadings, including heat generation, using the stress transfer function approach was investigated for reducing analysis process time and conservatism when compared to conventional analysis methods. Reduced conservatism provides margin that may be beneficial in life extension studies.

The increasing use of advanced high-strength steels in sheet metal forming processes requires improved knowledge concerning the thermal and contact conditions. This study presents the experimental and numerical analysis of tensile and draw-bead tests, considering a dual phase steel DP780. The temperature evolution was measured in both tests using an infrared thermal camera. The presented finite element model considers both the heat generated by plastic deformation and friction, as well as the heat loss to the environment by free convention and the contact conductance. The temperature rise in the uniaxial tensile test is accurately predicted by the numerical model. Regarding the draw-bead test, the pulling force is accurately predicted but the temperature variation is overestimated, requiring further investigation.