Giant Magnetoresistive Thin Films Research Articles

Thin film underlayer effects on mass resolving power in laser-assisted atom probe tomography

The effects of varying Co thickness on the mass resolving power for Cu in a multilayer stack are characterized by laser-assisted atom probe. As the Co layer thickness increased, Cu exhibited poorer mass resolving power. By reducing the pulse repetition rate from 250kHz to 10kHz, the mass resolving power improved to match that of Cu with no Co underlayer. These results support that thermal mechanisms for field evaporation dominate in this Co–Cu multilayer, which is a common architecture in giant magneto-resistance thin film devices.

Thin Film of Giant Magnetoresistance (GMR) Material Prepared by Sputtering Method

In recent decades, a new magnetic sensor based on magnetoresistance effect is highly researched and developed intensively. GMR material has great potential as next generation magnetic field sensing devices. It has also good magnetic and electric properties, and high potential to be developed into various applications of electronic devices such as: magnetic field sensor, current measurements, linear and rotational position sensor, data storage, head recording, and non-volatile magnetic random access memory. GMR material can be developed to be solid state magnetic sensors that are widely used in low field magnetic sensing applications. A solid state magnetic sensor can directly convert magnetic field into resistance, which can be easily detected by applying a sense current or voltage. Generally, there are many sensors for measuring the low magnetic field, such as: fluxgate sensor, Hall sensor, induction coil, GMR sensor, and SQUID sensor. Compared to other low magnetic field sensing techniques, solid state sensors have demonstrated many advantages, such as: small size (<0.1mm2), low power, high sensitivity (~0.1Oe) and good compatibility with CMOS technology. The thin film of GMR is usually prepared using: sputtering, electro deposition or molecular beam epitaxy (MBE) techniques. But so far, not many researchers reported the manufacture of thin film of GMR by dc-Opposed Target Magnetron Sputtering (dc-OTMS). In this paper, we inform the development of GMR thin film with sandwich and spin valve structures using dc-OTMS method. We have also developed organic GMR with Alq3 as a spacer layer.

Giant Magnetoresistance in (Ni<sub>60</sub>Co<sub>30</sub>Fe<sub>10</sub>/Cu) Trilayer Growth by Opposed Target Magnetron Sputtering

The giant magnetoresistance thin film of (Ni60Co30Fe10/Cu) trilayer were grown onto Si (100) substrate by dc-opposed target magnetron sputtering (dc-OTMS) technique. The growth parameters are: temperature of 100 0C, applied voltage of 600 volt, flow rate of Ar gas of 100 sccm, and growth pressure of 5.2 x10-1 Torr. The effects of Cu layer thickness and NiCoFe layer thickness on giant magnetoresistance (GMR) property of (Ni60Co30Fe10/Cu) trilayer were studied. We have found that the giant magnetoresistance (GMR) ratio of the sample was varied depend on the non-magnetic (Cu) layer thickness. The variation of Cu layer thickness presents an oscillatory behavior of GMR ratio. This oscillation reflects the exchange coupling oscillations between ferromagnetic and antiferromagnetic states, which are caused by an oscillation in the sign of the interlayer exchange coupling between ferromagnetic layers. The GMR ratio is change with increasing of NiCoFe layer thickness and presents GMR ratio of 70.0 % at tNiCoFe = 62.5 nm.

Design and Development of Magnetic Sensors Based on Giant Magnetoresistance (GMR) Materials

This paper describes magnetic sensors that have been developed in the last three years. GMR thin film materials have been successfully developed using unpinned CoFe/Cu/CoFe sandwiches on Si(100) substrate using a home built dc-opposed-target magnetron sputtering (OTMS). The magnetization of the sandwich is measured using hysteresis loop instrument, the Vibrating Sample Magnetometer (VSM). It was found that the phase of GMR was formed, with the MR ratio 15.76%.

Microfabrication and test of a magnetic field sensor using electrodeposited thin film of giant magnetoresistive (Cu/Co) x multilayers

Giant magnetoresistive (GMR) films of (Cu/Co) x multilayers have been successfully electrodeposited on a silicon substrate. An effort has also been made to microfabricate a sensor based on the electroplated GMR multilayers. Fabrication of the microsensor was implemented through computer-controlled electrodeposition of GMR thin films and lithographic patterning technology. The prototype microsensor shows a magnetoresistance ratio of ΔR/R=4% in a 3000 Gauss magnetic field. It was also found that the sensitivity of the prototype sensor is significantly affected at low fields by the patterning process.

Multilayer Structures with Giant Magnetoresistance

The phenomenological description of the giant magnetoresistance effect as well as the discussion of the requirements which must be fulfilled in giant magnetoresistance thin film structures are given in the first part of our review. In the second part the magnetization reversal and giant magnetoresistance effect of antiferromagnetically coupled multilayers, spin valve and pseudo-spin valve thin film structures are explained. For these structures we also discuss the influence of the structure defects such as surface roughness and pinholes on the giant magnetoresistance effect.

Spatial resolution measurement of giant magneto-resistance thin film

A system to measure magneto-resistance curves of thin films in a magnetic field of 40 Oe p–p at 2 MHz was developed, using a low noise, sheet-type four-terminal electrode. High intensity magnetic field was produced by resonance of a ferrite core electromagnet with a capacitor connected in parallel. The small size electrode enables measurements of spatial MR ratio distribution of a thin film on a 75 mm∅ silicon wafer.

Magnetic sensors for automotive applications

Magnetic sensors offer several key advantages: they allow contactless and, consequently, wear-free measurement of mechanical quantities like angle of rotation and angular speed. They are robust and inexpensive to manufacture. As one example of magnetic sensors in production at Robert Bosch GmbH, the steering wheel sensor LWS3 is shown, developed for the electronic stability program (ESP), which prevents vehicles from spinning. We recently demonstrated, that the inherent limitation of the AMR-effect to an 180° angular range can be overcome by using a switchable magnetic field generated inside the sensor element. For a new generation of magnetic sensors, the technology of giant magneto-resistance (GMR) thin film systems promises several advantages like larger working distances, more precise angular position measurement in a wider range (up to 360°), smaller and therefore cheaper sensor chips and economic system solutions due to the higher signal output. A GMR multilayer system of CoCu/Cu was developed, which fulfills the requirement of having no hysteresis in the magneto-resistive characteristics. On the other hand, research is still going on for sensitive GMR layers, which are stable at temperatures of 200°C (or more) for long time periods of at least 500 h. Thin film systems of spin valve type, used in read heads for disc drives, have been thoroughly evaluated about whether they can be used in sensors for automotive applications. The great challenge is to generate GMR thin film systems which cover a much wider range of features than the existing technologies of Hall and AMR and which can be produced at lower cost. Only versatile GMR sensors will lead to high production volumes, which are needed for a cost efficient fabrication as in other modern micro technologies.

Giant magnetoresistive thin films of (La,Pr)0.7(Ca,Sr)0.3MnO3 prepared by aerosol MOCVD

It has been demonstrated that high quality thin films of Ln 1-x M x MnO 3 can be successfully prepared by aerosol MOCVD at 750 °C from volatile thd complexes. Subsequent annealing in oxygen at 750 °C is necessary to stabilize the oxygen content of the films. XRD patterns of the films showed them to be pseudocubic with an apparent lattice parameter linear in the average ionic radius of Ln and M. The evolution of Ln 1-x M x MnO 3 film morphology with increasing the film thickness has also been studied. The morphological instability of the MOCVD process results in the formation of a hillocky surface with thickness >2000 A. The electrical properties of La 1-x Ca x MnO 3 and La 1-x Sr x MnO 3 correlate with those reported for bulk and thin film materials. The substitution of Pr for La in La 1-x Sr x MnO 3 reduces the maximum resistivity temperature, T p , non-linearly. La 1-x Ca x MnO 3 thin films reveal a shift of T p downwards in the case of substrate materials with a positive lattice mismatch with the films. La 0.35 Pr 0.35 Ca 0.3 MnO 3 /LaAlO 3 demonstrates a very complex temperature dependence of the resistivity, which is described using a conceptual phase diagram of Ln 1-x M x MnO 3 . A marked GMR effect was observed for La 0.35 Pr 0.35 Ca 0.3 MnO 3 /LaAlO 3 below 21 K (ca. 10 10 %) and at ca. 70 K even in a field of 1 T.

Low-energy ion beam-assisted deposition of giant magnetoresistive thin films

Granular and multilayer Co-Ag and NiFe-Ag thin films have been prepared by magnetron sputtering and by concurrent low-energy (0–500 eV) ion radiation-assisted deposition. The ion beam bombardment slightly increased the giant magnetoresistance of granular films and then progressively decreased it. X-ray data revealed a change in the crystalline structure of these films, dependent on the energy of the beam. Examination using transmission electron microscopy (TEM) also highlighted differences between the as-sputtered and the ion beam-assisted films. For multilayer films, TEM and x-ray analysis shows changes in the interfacial and crystal structure induced by the ion beam.

Thin film structures for low field granular giant magnetoresistance

Giant magnetoresistance (GMR) is a relatively new field of study pursued by scientists and technologists alike. A potential application of GMR thin films is the replacement of NiFe alloy thin films (having anisotropic magnetoresistance) to obtain greater signal. Applications of this type require that the GMR be obtained at low fields, on the order of 10 Oe. In this paper three types of granular GMR thin film structures are described: co-deposited heterogeneous alloys, granular bi-layers, and discontinuous multilayers. Experimental examples of each type are presented, and the field dependence of GMR for each structure is discussed. Only discontinuous multilayer thin film structures have shown suitable GMR at low fields, and the properties and microstructure of these thin films will be described in greater detail.