Arif Ozbay

Low frequency magnetoresistive noise in spin-valve structures

We report on resistance noise in spin-valve structures that is due to reconfigurations in domain structure of the magnetic layers. 1/f noise from the free layer and pinned layer is evident and its magnitude is in good agreement with predictions from the fluctuation dissipation relation using the imaginary (dissipative) component of the measured resistance susceptibility. In addition, we find that the imaginary component is dependent on applied magnetic field, being larger for layers that exhibit pronounced magnetic hysteresis. A magnetoresistive 1/f noise parameter is proposed, and benchmark values for a variety of spin-valve devices are reported.

Large magnetoresistance of thick polymer devices having La0.67Sr0.33MnO3 electrodes

We report magnetoresistance (MR) measurements for structures with micrometer-thick regioregular, polythiophene (rr-P3HT) polymer layers between two ferromagnetic contacts. Hole spin transport through the polymer layer leads to a relative MR value in 300 mT fields of 0.3% at 300 K and increasing to 18% at 25 K. The inferred intrinsic spin lifetime and diffusion length are about 7 ms and 0.4 μm, respectively. The spin transport coherence length is enhanced by the electric field, leading to an enhancement in MR with increasing applied voltage.

Magnetic-Field Dependence of the Noise in a Magnetoresistive Sensor Having MEMS Flux Concentrators

We report the dc and ac magnetic field dependence of the low-frequency noise in a microelectromechanical system (MEMS) flux concentrator device containing a giant magnetoresistance spin valve (SV). The noise is dominated by resistance fluctuations having a magnetic origin. Under nominally zero magnetic-field biasing conditions, the noise power is large and varies rapidly with small changes in magnetic field. Metastability between distinct resistive states is observed and can be suppressed with the application of a moderate longitudinal field. Stationary flux concentrators do not contribute excess noise, rather the dominant source of noise is the SVs themselves. This result indicates that the device is likely to increase the sensitivity of many magnetic sensors at low frequencies by orders of magnitude

Effects of flux concentrators on the low frequency noise in magnetoresistive sensing devices

This paper investigated the effects of flux concentrators (FCs) on magnetic 1/f noise in magnetoresistive sensing devices. This is done by comparing results for the cases of bare (without FCs) sensors and those with FCs. It is shown that FCs can be a source of broad-band low frequency noise in AC MEMS flux concentrator device when the signal modulation amplitudes are sufficiently high.

COMPACTION AND DENSITY FLUCTUATIONS IN VIBRATED GRANULAR MEDIA

We report measurements of the density of a vibrated granular material as a function of time or taps. The material studied consists of monodisperse spherical glass beads confined to a long, thin cylindrical tube. Changes in vibration intensity are used to induce transitions between two steady state densities that depend on the intensity of the vibrations. We find a complex time evolution similar to previous work on the irreversible relaxation from a loose state toward a steady state. In addition, frequency dependent third order moments of the density fluctuations are measured. The data indicate a coupling between large variations in density on one time scale and noise power over a broad range of higher-frequency scales.