Fractional Differential Equations

The theory of affordances

Many current neurophysiological, psychophysical, and psychological approaches to vision rest on the idea that when we see, the brain produces an internal representation of the world. The activation of this internal representation is assumed to give rise to the experience of seeing. The problem with this kind of approach is that it leaves unexplained how the existence of such a detailed internal representation might produce visual consciousness. An alternative proposal is made here. We propose that seeing is a way of acting. It is a particular way of exploring the environment. Activity in internal representations does not generate the experience of seeing. The outside world serves as its own, external, representation. The experience of seeing occurs when the organism masters what we call the governing laws of sensorimotor contingency. The advantage of this approach is that it provides a natural and principled way of accounting for visual consciousness, and for the differences in the perceived quality of sensory experience in the different sensory modalities. Several lines of empirical evidence are brought forward in support of the theory, in particular: evidence from experiments in sensorimotor adaptation, visual \"filling in,\" visual stability despite eye movements, change blindness, sensory substitution, and color perception.

A sensorimotor account of vision and visual consciousness-Authors' Response-Acting out our sensory experience

The authors observed tunnel magnetoresistance (TMR) ratio of 604% at 300K in Ta∕Co20Fe60B20∕MgO∕Co20Fe60B20∕Ta pseudo-spin-valve magnetic tunnel junction annealed at 525°C. To obtain high TMR ratio, it was found critical to anneal the structure at high temperature above 500°C, while suppressing the Ta diffusion into CoFeB electrodes and in particular to the CoFeB∕MgO interface. X-ray diffraction measurement of MgO on SiO2 or Co20Fe60B20 shows that an improvement of MgO barrier quality, in terms of the degree of the (001) orientation and stress relaxation, takes place at annealing temperatures above 450°C. The highest TMR ratio observed at 5K was 1144%.

/pdf/tunnel-magnetoresistance-of-604-at-300k-by-suppression-of-ta-2yiy65l5s3.pdf

Tunnel magnetoresistance of 604% at 300K by suppression of Ta diffusion in CoFeB∕MgO∕CoFeB pseudo-spin-valves annealed at high temperature

https://cyberleninka.org/article/n/296274.pdf

Magnetic tunnel junctions

Spin dependent tunnel junctions showing tunnel magnetoresistance (TMR) values of 39/spl sim/41% were fabricated using Ion Beam Deposition (IBD). Both the electrodes and the aluminum layer deposition were done by IBD. The aluminum oxidation was performed using the assist gun with an oxygen beam (+30 V acceleration voltage applied on the grids) using mixed O/sub 2//Ar plasma. The oxidation was monitored in real time with a residual gas analyzer (RGA). The junction area is defined by lithography, down to 3/spl times/2 /spl mu/m/sup 2/. As-deposited junctions with 15 /spl Aring/ of Al showed TMR of 27/spl sim/29%, independent of the junction area, with resistance-area products of 0.8/spl sim/1.6 M/spl Omega//spl times//spl mu/m/sup 2/. This TMR value reached 40% upon annealing at 290/spl deg/C, with resistance decreasing to 0.5/spl sim/0.8 M/spl Omega//spl times//spl mu/m/sup 2/.

Ion beam deposition and oxidation of spin-dependent tunnel junctions

Low frequency noise and small output voltage are the strongest limitations to the use of magnetic tunnel junctions (MTJs) for magnetic sensor applications, replacing giant magnetoresistance (GMR) and anisotropic magnetoresistance sensors. In this paper, we explore the possibility of using arrays with a large number of MTJs connected in parallel/series to overcome these limitations. MTJ’s sensor arrays of more than 3×103 junction elements in different configurations have been fabricated. Low frequency noise and detectivity have been measured and compared to an analytical model, with detectivities of about 16 nT/Hz1/2 achieved in a series/parallel architecture. This detectivity levels are competitive with single devices based on GMR, with the advantage of not requiring additional flux concentrators.

Low frequency noise in arrays of magnetic tunnel junctions connected in series and parallel

This paper describes how magnetoresistive materials can be optimized and integrated in magnetic field sensor devices. Giant magnetoresistive (GMR) and tunnel magnetoresistive (TMR) can provide advantageous solutions for a wide range of applications, of which some are described here. Considerations on field sensitivities, intrinsic noise mechanisms, biasing, and integration schemes are presented.

Spintronic Sensors

The magnetic field detection limit of spin valve sensors in the thermal noise regime is improved from 1.3 nT/Hz1/2 to 0.064 nT/Hz1/2 by incorporating a Co93Zr3Nb 4 soft magnetic flux guide concentrator structure. Linear spin valve sensors were processed down to 20times2 mum2 dimensions, with and without an additional 3500-Aring-thick flux guide concentrator, with a magnetic flux gain factor ranging from 5 to 20. Spin valves show a starting sensitivity of 0.2 %/Oe, improved to 3.8 %/Oe with the flux concentrator. Noise measurements from dc to 500 kHz were performed, indicating similar noise levels with and without flux concentrators. In terms of magnetic field detection, sensors with flux concentrators show a detection limit of 2 nT/Hz1/2 at 10 Hz, compared to 47 nT/Hz1/2 without flux concentrators. No additional 1/f noise is measured in the spin valve sensor response upon the addition of the soft magnetic flux concentrators in the frequency range studied

Improving Magnetic Field Detection Limits of Spin Valve Sensors Using Magnetic Flux Guide Concentrators

Spin dependent tunnel junctions with TMR exceeding 30-40% can now be prepared with AlO/sub x/ and AlN barriers, with junction resistance tuned from 30-40 /spl Omega//spl times//spl mu/m/sup 2/ to 10/sup 8/ /spl Omega//spl times//spl mu/m/sup 2/. Thermal stability is better than 3000% for thicker barriers (>11 /spl Aring/) but is degraded to 220/spl deg/C for 6 /spl Aring/ barriers. A 9 bit MRAM cell is demonstrated using tunnel junctions and vertically integrated a:Si diodes. Junction switching is achieved with on chip 20 ns field pulses. Requirements for tunnel junctions for 100 Gb/in/sup 2/ read head applications are discussed. First prototypes of tunnel junction read heads with 600 /spl Aring/ read gaps were fabricated, where the TJ is at the air bearing surface. TMR loss was observed during the final head lapping steps.

Ricardo Ferreira

Papers

Ion beam deposition and oxidation of spin-dependent tunnel junctions

Low frequency noise in arrays of magnetic tunnel junctions connected in series and parallel

Spintronic Sensors

Improving Magnetic Field Detection Limits of Spin Valve Sensors Using Magnetic Flux Guide Concentrators

Spin dependent tunnel junctions for memory and read-head applications