Magnetoresistive sensors based on the elasticity of domain walls

Magnetic sensors based on the magnetoresistance effects have a promising application prospect due to their excellent sensitivity and advantages in terms of the integration. However, competition between higher sensitivity and larger measuring range remains a problem. Here, we propose a novel mechanism for the design of magnetoresistive sensors: probing the perpendicular field by detecting the expansion of the elastic magnetic Domain Wall (DW) in the free layer of a spin valve or a magnetic tunnel junction. Performances of devices based on this mechanism, such as the sensitivity and the measuring range can be tuned by manipulating the geometry of the device, without changing the intrinsic properties of the material, thus promising a higher integration level and a better performance. The mechanism is theoretically explained based on the experimental results. Two examples are proposed and their functionality and performances are verified via micromagnetic simulation.Comment: 4 figures, 13 page

Interlayer magnetic coupling in iron layered structures

In this thesis the magnetic coupling between iron layers across nonmagnetic metal interlayers has been investigated by means of magneto-optic methods. The epitaxial growth and crystalline quality of the layered structures were controlled by RHEED, SPA-LEED and AES techniques. Magnetic properties of ultrathin Fe films from 1.5 to 16 atomic layers have been studied by Brillouin light scattering (BLS) and magneto-optic Kerr effect (MaKE). Interlayer coupling in Cr spacer systems has been investigated systematically. On large GaAs substrates two period oscillations in the coupling as a function of the interlayer thickness have been observed, the thermal stability and temperature dependence of the coupling have been investigated up to 700K. The oscillation periods and the attenuation of the oscillation amplitudes can be understood with the help of the nesting effect in the Fermi-surface of Cr, on the basis of RKKY type interaction. The origin of biquadratic coupling and absence of phase-slips in the fine oscillations have been interpreted as due to reduced quality of the crystalline structure of the Cr interlayer and the Fe/Cr interfaces. The influence of interface roughness on oscillatory coupling has been studied by adding an Ag layer between the Cr interlayer. The additional Ag layer results in weaker bilinear coupling, but stronger biquadratic exchange due to introducing interface roughness. The two period oscillations of the magnetic coupling across noble metal spacers can be reproduced on the basis of the R-l<.-.KY type interaction theory. It has been confirmed in the case of the noble metals that the oscillatory periods depend on the extremal distances in the Fermi-surfaces of the interlayer elements. Annealing investigations on the coupling have been performed in the layered structures with different interlayers. Both the structure effect of the interlayer and the interface effect have been observed in Cu-Au alloy systems. Antiferromagnetic coupling in these systems can be largely enhanced after annealing at an appropriate temperature due to improvement of the interlayer crystallinity. In addition, in an Au/Cu superlattice spacer structure an antiferromagnetic coupling has been observed after annealing, which coupled ferromagneticallybefore the annealing

Interlayer magnetic coupling in iron layered structures

In this thesis the magnetic coupling between iron layers across nonmagnetic metal interlayers has been investigated by means of magneto-optic methods. The epitaxial growth and crystalline quality of the layered structures were controlled by RHEED, SPA-LEED and AES techniques. Magnetic properties of ultrathin Fe films from 1.5 to 16 atomic layers have been studied by Brillouin light scattering (BLS) and magneto-optic Kerr effect (MOKE). Interlayer coupling in Cr spacer systems has been investigated systematically. On large GaAs substrates two period oscillations in the coupling as a function of the interlayer thickness have been observed, the thermal stability and temperature dependence of the coupling have been investigated up to 700K. The oscillation periods and the attenuation of the oscillation amplitudes can be understood with the help of the nesting effect in the Fermi-surface of Cr, on the basis of RKKY type interaction. The origin of biquadratic coupling and absence of phase-slips in the fine oscillations have been interpreted as due to reduced quality of the crystalline structure of the Cr interlayer and the Fe/Cr interfaces. The influence of interface roughness on oscillatory coupling has been studied by adding an Ag layer between the Cr interlayer. The additional Ag layer results in weaker bilinear coupling, but stronger biquadratic exchange due to introducing interface roughness. The two period oscillations of the magnetic coupling across noble metal spacers can be reproduced on the basis of the RKKY type interaction theory. It has been confirmed in the case of the noble metals that the oscillatory periods depend on the extremal distances in the Fermi-surfaces of the interlayer elements. Annealing investigations on the coupling have been performed in the layered structures with different interlayers. Both the structure effect of the interlayer and the interface effect have been observed in Cu-Au alloy systems. Antiferromagnetic coupling in these systems can be largely enhanced after annealing at an appropriate temperature due to improvement of the interlayer crystallinity. In addition, in an Au/Cu superlattice spacer structure an antiferromagnetic coupling has been observed after annealing, which coupled ferromagnetically before the annealing. (orig.)Available from TIB Hannover: RA 831(2934) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Modulation of interlayer exchange coupling strength in magnetic tunnel junctions via strain effect

Interlayer exchange coupling of two ferromagnetic electrodes separated by a thin MgO tunnel barrier is investigated using magneto-optical Kerr effect. We find that the coupling field can be reduced by more than 40% as the thickness of a top Ta capping layer increases from 0.5 to 1.2 nm. In contrast, a similar film stack with an additional 3 nm Ru capping layer displays no such dependence on Ta thickness. Transmission electron microscopy study shows that the oxidation of the exposed Ta capping layer induces changes in the crystalline structures of the underlying films, giving rise to the observed reduction of the interlayer coupling field

Design and Fabrication of Full Wheatstone-Bridge-Based Angular GMR Sensors

Since the discovery of the giant magnetoresistive (GMR) effect, GMR sensors have gained much attention in last decades due to their high sensitivity, small size, and low cost. The full Wheatstone-bridge-based GMR sensor is most useful in terms of the application point of view. However, its manufacturing process is usually complex. In this paper, we present an efficient and concise approach to fabricate a full Wheatstone-bridge-based angular GMR sensor by depositing one GMR film stack, utilizing simple patterned processes, and a concise post-annealing procedure based on a special layout. The angular GMR sensor is of good linear performance and achieves a sensitivity of 0.112 mV/V/Oe at the annealing temperature of 260 &deg;C in the magnetic field range from &minus;50 to +50 Oe. This work provides a design and method for GMR-sensor manufacturing that is easy for implementation and suitable for mass production

Reversal of the Pinning Direction in the Synthetic Spin Valve with a NiFeCr Seed Layer

The effect of the seed layers on the magnetic properties of the giant magnetoresistance thin films has received a lot of attention. Here, a synthetic spin valve film stack with a wedge-shaped NiFeCr seed layer is deposited and annealed following a zero-field cooling procedure. The film crystallinity and magnetic properties are studied as a function of the NiFeCr seed layer thickness. It is found that the exchange coupling field from the IrMn/CoFe interface and the antiferromagnetic coupling field in the synthetic antiferromagnet both increase as the seed layer thickness increases, indicating the perfection of film texture. In this film, the critical thickness of the NiFeCr seed layer for the formation of the ordered IrMn3 texture is about 9.3 nm. Meanwhile, a reversal of the pinning direction in the film is observed at this critical thickness of NiFeCr. This phenomenon can be explained in a free energy model by the competition effect between the exchange coupling and the interlayer coupling during the annealing process

Fast Tunable Biological Fluorescence Detection Device with Integrable Liquid Crystal Filter

Detecting a variety of biological samples accurately and swiftly in an integrated way is of great practical significance. Currently, biofluorescent spectrum detection still largely relies on microscopic spectrometers. In this study, we propose an integrable method to detect biofluorescent spectrums with designed liquid crystal tunable filter (LCTF), in order to identify typical biological samples such as cells and bacteria. Hela cells labeled with red and green fluorescent proteins and Pseudomonas with fluorescence wavelengths of 610 nm, 509 nm and 450 nm, respectively, are inspected. High-resolution (6 μm) biofluorescent results have been achieved, together with clear images of the Hela cell clusters and the Pseudomonas bacteria colonies. Biofluorescence signals can be detected at a high transmittance (above 80%), and the response time of the device can reach 20 ms or below. The proposed method has the potential to be integrated into a microfluidic system to detect and identify the biofluorescent signals as a high throughput, low-cost option, for both high resolution and large field observation applications