GMR Response Research Articles

Micromagnetic simulations on detection of magnetic labelled biomolecules using MR sensors

In this work, we present a study of the interaction between the magnetic particles used in biological applications and the giant magnetoresistive effect (GMR) sensor. The fractional change in resistance, and hence the sensitivity, will be maximized by matching, as far as possible, the size of the sensor to the size of the beads and by carefully positioning the beads over the sensor. We found, by micromagnetic simulations, that the amount of the surface coverage with magnetic particles may affect the magnetization curve of the sensor and will change the field dependence of the GMR response.

Magnetic and magnetotransport properties in Joule-heated granular Cu 95Co 5 ribbons

Cu 95Co 5 alloys, consisting of Co nanoparticles, were obtained by subjecting rapidly quenched ribbons to suitable dc Joule-heating treatments (0 ≤ I ≤ 5.75 A for 60 s) in order to induce different degrees of Co precipitation with particles having different average size. The behaviour of the resistance versus applied field is influenced by the structural changes (Co cluster formation) that occur in the samples after different thermal treatments. The dependance of the electric and magnetic properties on microstructural configurations has been studied by measuring room-temperature hysteresis loops and GMR. By combining the GMR response with magnetization data, information on the magnetic correlation between magnetic moments of neighbouring Co particles will be obtained and correlated to the different microstructures induced by current annealing.

Rotating-field magnetoresistance of exchange-biased spin valves

We investigate the magnetoresistance (MR) of spin valves by (i) varying the strength of the field applied in a fixed direction and (ii) rotating the field with fixed strength. The latter data reflect in general a mixture of giant and anisotropic magnetoresistance (GMR and AMR). We present an experimental procedure to suppress the AMR contributions of all ferromagnetic layers in the spin valve without disturbing the GMR response. The resulting angular MR curves are fitted with a single-domain model to determine with high precision the exchange bias field, the uniaxial anisotropies, the GMR ratio, and the interlayer coupling field. The application of the method to differently prepared Ta(5.0nm)∕NiFe(3.0nm)∕FeMn(15.5nm)∕NiFe(3.0nm)∕Co(2.0nm)∕Cu(3.5nm)∕Co(2.0nm)∕NiFe(7.0nm) spin valves with GMR ratios of 1.8% and 4% demonstrates the sensitivity and reveals differences of the order of a few percents of the exchange bias field for the uniaxial anisotropy fields of the free and pinned layer as well as for the interlayer coupling field.

ＧＭＲヘッド再生シールドの突発的透磁率変化

The magnetostatic interaction between the GMR elements and the shields of shielded GMR heads was investigated by micromagnetic modeling of the GMR elements and the shields. The magnetization patterns in the shields were determined in order to minimize the total energy of the shields. The biasing field of the GMR element was defined by the sum of the permanent magnet field and its images in the shields. It was confirmed that the magnetization curves of shields with permanent magnets show hysteric behavior, and double- or single-flux closure appeared in the domain structure. The transition from double-flux closures to a single-flux closure causes sudden permeability change in the shields. A permeability change will produce changes in the imaging field of the permanent magnets in the shields. As a result, a Barkhausen jump corresponding to a permeability change appears in the easy-axis transfer curves (i.e., the GMR response vs. the easy-axis field).

Electrical transport in metallic thin films for giant magnetoresistance modelling purposes

A method is presented to determine the mean free path in individual layers of giant magnetoresistive samples from experimental data. The boundary conditions at the surfaces of the thin films are fixed at certain positions within the stack by the implementation of foreign atoms. The scattering activities of these atoms are analysed by means of the GMR response of specially designed samples. An analytical expression is used to model the variation of the sheet conductance as a function of the thickness of Cu and Co thin sputtered films. The data of Cu are well reproduced by means of a single bulk mean free path, whereas for Co, a spin dependence of the mean free paths is needed.

GMR in DC magnetron sputtered Ni/sub 81/Fe/sub 19//Cu multilayers

In this paper, we present results of a study on Ni/sub 81/Fe/sub 19/Cu MLs deposited using a four-source DC magnetron sputtering system operated in planetary mode. A significant change of GMR value with deposition conditions, especially base pressure and deposition pressure, has been observed for Ni/sub 18/Fe/sub 19//Cu MLs. With an optimized process, we have obtained a GMR response of 9.5% with a field sensitivity of 0.44%/Oe for Si/[(Ni/sub 81/Fe/sub 19/)17 /spl Aring//Cu20 /spl Aring/]/sub 20/ MLs without an Fe buffer layer. The insertion of a very thin layer of a second magnetic species at nonmagnetic/magnetic interfaces in the ML stack makes GMR response either sensitive or less sensitive to deposition conditions depending on the species selected. We believe that the key to obtaining large GMR values in Ni/sub 81/Fe/sub 19//Cu MLs lies in the control of layered structure and interfacial chemistry. In addition, these Ni/sub 81/Fe/sub 19//Cu MLs survive high temperature annealing up to 250/spl deg/C, retaining a GMR value of 8.5%. The thermal stability exhibited by these MLs over the temperature range for device fabrication makes them valuable for high density recording head sensor applications.

Improved performance of Cu-Co CPP GMR sensors

We have fabricated and tested GMR magnetic sensors that operate in the CPP mode. This work is a continuation of the ultra-high density magnetic sensor research introduced at INTERMAG 96. We have made two significant modifications to the process sequence. First, contact to the sensor is made through a metal conduit deposited in situ with the multilayers. This deposition replaces electroplating. This configuration ensures a good electrical interface between the top of multilayer stack and the top contact, and a continuous, conductive current path to the sensor. The consequences of this modification are an increase in yield of operational devices to /spl ges/90% per wafer and a significant reduction of the device resistance to /spl les/560 m/spl Omega/ and of the uniformity of the device resistance to /spl les/3%. Second, the as-deposited multilayer structure has been changed from [Cu 30 /spl Aring//Co 20 /spl Aring/]/sub 18/ (third peak) to [Cu 20.5 /spl Aring//Co 12 /spl Aring/]/sub 30/ (second peak) to increase the GMR response. The best second peak CPP GMR response from a single device is 39%. The sensitivity of that device is 0.13 %/Oe.

GMR of Co/Cu multilayers with reduced hysteresis and low-field response

We present results of a study on optimization of the magnetoresistance (GMR) response in Co/Cu multilayers (MLs) for Cu layer thickness near the second oscillatory peak. Co/Cu MLs with alternating thick (t/sup (1)//sub Co/) and thin (t/sup (2)//sub Co/) Co layers have been prepared in the form of [Cot/sup (1)//sub Co/ /spl Aring//Cu20 /spl Aring//Cot/sup (2)//sub Co/ /spl Aring//Cu20 /spl Aring/]/sub 15/. We have found that the magnetoresistive hysteresis of these MLs is reduced with decreasing t/sup (2)//sub Co/ and has disappeared when t/sup (2)//sub Co/<4.5 /spl Aring/. We have obtained an optimal GMR response with a field sensitivity of 0.13%/0e over a field region of /spl sim/60 Oe centered at /spl sim/50 Oe. This architecture may enable the use of Cu/Co MLs in low-field magnetic sensor applications.

Application of giant magnetoresistive elements in thin film tape heads

We studied the applicability of Ni/sub 80/Fe/sub 20//Cu/Ni/sub 80/Fe/sub 20//Fe/sub 50/Mn/sub 50/ GMR multilayers for thin film tape heads. A method involving crossed anisotropies is applied for avoiding noise in the GMR response. We compare and analyse the sensitivities of AMR and GMR heads.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>