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Author(s): Junho Seo [sup.1] [sup.2] , Chandan De [sup.1] [sup.3] , Hyunsoo Ha [sup.4] , Ji Eun Lee [sup.5] , Sungyu Park [sup.1] , Joonbum Park [sup.6] , Yurii Skourski [...], Efficient magnetic control of electronic conduction is at the heart of spintronic functionality for memory and logic applications.sup.1,2. Magnets with topological band crossings serve as a good material platform for such control, because their topological band degeneracy can be readily tuned by spin configurations, dramatically modulating electronic conduction.sup.3-10. Here we propose that the topological nodal-line degeneracy of spin-polarized bands in magnetic semiconductors induces an extremely large angular response of magnetotransport. Taking a layered ferrimagnet, Mn.sub.3Si.sub.2Te.sub.6, and its derived compounds as a model system, we show that the topological band degeneracy, driven by chiral molecular orbital states, is lifted depending on spin orientation, which leads to a metal-insulator transition in the same ferrimagnetic phase. The resulting variation of angular magnetoresistance with rotating magnetization exceeds a trillion per cent per radian, which we call colossal angular magnetoresistance. Our findings demonstrate that magnetic nodal-line semiconductors are a promising platform for realizing extremely sensitive spin- and orbital-dependent functionalities. A study reports a colossal angular magnetoresistance in the topological magnet Mn.sub.3Si.sub.2Te.sub.6, resulting from a metal-to-insulator transition caused by controlled lifting of a topological band degeneracy, and discusses the key parameters involved.

Author(s): Gaël Grissonnanche [sup.1] [sup.2] [sup.3] , Yawen Fang [sup.2] , Anaëlle Legros [sup.1] [sup.4] , Simon Verret [sup.1] , Francis Laliberté [sup.1] , Clément Collignon [sup.1] , Jianshi Zhou [...], A variety of 'strange metals' exhibit resistivity that decreases linearly with temperature as the temperature decreases to zero.sup.1-3, in contrast to conventional metals where resistivity decreases quadratically with temperature. This linear-in-temperature resistivity has been attributed to charge carriers scattering at a rate given by h/[tau] = [alpha]k.sub.BT, where [alpha] is a constant of order unity, h is the Planck constant and k.sub.B is the Boltzmann constant. This simple relationship between the scattering rate and temperature is observed across a wide variety of materials, suggesting a fundamental upper limit on scattering--the 'Planckian limit'.sup.4,5--but little is known about the underlying origins of this limit. Here we report a measurement of the angle-dependent magnetoresistance of La.sub.1.6-xNd.sub.0.4Sr.sub.xCuO.sub.4--a hole-doped cuprate that shows linear-in-temperature resistivity down to the lowest measured temperatures.sup.6. The angle-dependent magnetoresistance shows a well defined Fermi surface that agrees quantitatively with angle-resolved photoemission spectroscopy measurements.sup.7 and reveals a linear-in-temperature scattering rate that saturates at the Planckian limit, namely [alpha] = 1.2 [plus or minus] 0.4. Remarkably, we find that this Planckian scattering rate is isotropic, that is, it is independent of direction, in contrast to expectations from 'hotspot' models.sup.8,9. Our findings suggest that linear-in-temperature resistivity in strange metals emerges from a momentum-independent inelastic scattering rate that reaches the Planckian limit. Angle-dependent magnetoresistance measurements of a strange-metal phase of a hole-doped cuprate show a well defined Fermi surface and an isotropic linear-in-temperature scattering rate that saturates at the Planckian limit.

Many unusual behaviors in complex oxides are deeply associated with the spontaneous emergence of microscopic phase separation. Depending on the underlying mechanism, the competing phases can form ordered or random patterns at vastly different length scales. By using a microwave impedance microscope, we observed an orientation-ordered percotating network in strained [Nd.sub.1/2][Sr.sub.1/2]Mn[O.sub.3] thin firms with a large period of 100 nanometers. The filamentary metallic domains align preferentially along certain crystal axes of the substrate, suggesting the anisotropic elastic strain as the key interaction in this system. The total impedance maps provide microscopic etectrical information of the hysteretic behavior in strained thin film manganites, suggesting dose connection between the glassy order and the colossal magnetoresistance effects at tow temperatures. 10.1126/science.1189925

The signature of correlated electron materials (CEMs) is the coupling between spin, charge, orbital and lattice resulting in exotic functionality. This complexity is directly responsible for their tunability. We demonstrate here that the broken symmetry, through cubic to orthorhombic distortion in the lattice structure in a prototype manganite single crystal, [La.sub.0.69][Ca.sub.0.31]Mn[O.sub.3], leads to an anisotropic magneto-elastic response to an external field, and consequently to remarkable magneto-transport behavior. An anomalous anisotropic magnetoresistance (AMR) effect occurs close to the metal-insulator transition (MIT) in the system, showing a direct correlation with the anisotropic field-tuned MIT in the system and can be understood by means of a simple phenomenological model. A small crystalline anisotropy stimulates a 'colossal' AMR near the MIT phase boundary of the system, thus revealing the intimate interplay between magneto- and electronic-crystalline couplings. metal-insulator transition | CEM

Problem statement: Microstructure of the grain will influence the properties of a polycrystalline manganites when different dopant is introduced. In this work, an effort had been made to investigate the influence of Ca, Ba and Sr substitution in La site. Approach: Polycrystalline manganites compound of [La.sub.0.67][A.sub.0.33]Mn[O.sub.3] where A = Ba, Sr and Ca had been prepared via conventional solid-state reaction method. The structure, microstructure, magnetic and electrical properties had been investigated using XRD, SEM, VSM and four-point probe techniques. Results: XRD spectrums showed that LBMO and LCMO were in single-phase orthorhombic structure whereas LSMO was rhombohedral structure. Scanning electron micrographs showed that LSMO had smaller average grain size as compared to LBMO. However, for LCMO, there was no clear grain boundary that can be observed and all the grains were well connected. The difference in the microstructure image might be due to the variance A-site cation that differs in grain growth. The Curie temperature, [T.sub.c] of LBMO and LSMO was 343.0 and 363.5 K, respectively. But the [T.sub.c] for LCMO was lower then 300 K. The [T.sub.p] for LCMO was 215 K while it was near or above 300K for LBMO and LSMO. All samples showed extrinsic Magnetoresistance (MR) effect. Higher MR was observed well below [T.sub.c] or [T.sub.p] where MR value increased monotonically with the decrease of temperature. This was associated with the different grain and grain boundary formation when different cation was substituted. LCMO displayed the highest low-field MR value (-15.82% at 0.2 T, 90 K) and high-field MR (-25.60% at 1 T, 300 K). Conclusion: Hence, electrical and magnetic transition temperature ([T.sub.p] and [T.sub.c]) were affected by the average A-site cation radius. Key words: Ceramic, low field magnetoresistance, magnetoresistance, INTRODUCTION In recent year there has been a lot of research study in Colossal Magnetoresistance (CMR) effects in rare-earth manganite perovskite with general formula [La.sub.[1-x]][A.sub.x]Mn[O.sub.3] (A = Ba, Sr, Pb [...]

For automotive applications like steering wheel position, sensing the angular position of a mechanical axel is detected in a contactless way: a small permanent magnet at the end of the shaft is magnetized perpendicularly to the axis of rotation, and a magnetic field sensor is placed ahead. Even though the magnetic field sensor may be calibrated to have virtually no errors, assembly tolerances of the magnet and the sensor lead to errors in the estimated angular position of the shaft. A Taylor series expansion of the magnetic field up to second order is used to approximate these angle errors. Results of Monte-Carlo simulations show that worst case angle errors may be up to 10 times the average angle error due to error propagation in the nonlinear goniometric relationships. Various shapes of magnets are discussed and criteria for optimization are given. The strong effects of magnet size and distance between sensor and magnet are explained and the limit of infinite homogeneous magnetic field is derived. The results can be used to anticipate production spread of angle sensor systems. Index Terms--Angle errors, assembly tolerances, giant magnetoresistance, magnetic angle sensor, production spread.

We used a lightly phosphorus-doped, n-type-silicon (n-Si) substrate. Figure la shows the temperature dependence of the mobility, μ, and the carrier density, n, of the substrate, whose behaviours are just [...], Recent discoveries of large magnetoresistance in non-magnetic semiconductors (1-8) have gained much attention because the size of the effect is comparable to, or even larger than, that of magnetoresistance in magnetic systems (9-14). Conventional magnetoresistance in doped semiconductors is straightforwardly explained as the effect of the Lorentz force on the carrier motion (15), but the reported unusually large effects imply that the underlying mechanisms have not yet been fully explored. Here we report that a simple device, based on a lightly doped silicon substrate between two metallic contacts, shows a large positive magnetoresistance of more than 1,000 per cent at room temperature (300 K) and 10,000 per cent at 25 K, for magnetic fields between 0 and 3 T. A high electric field is applied to the device, so that conduction is space-charge limited (16-18). For substrates with a charge carrier density below [~10.sup.13] [cm.sup.-3], the magnetoresistance exhibits a linear dependence on the magnetic field between 3 and 9 T. We propose that the observed large magnetoresistance can be explained by quasi-neutrality breaking of the space-charge effect, where insufficient charge is present to compensate the electrons injected into the device. This introduces an electric field inhomogeneity, analogous to the situation in other semiconductors in which a large, non-saturating magnetoresistance was observed (1-5,19), In this regime, the motions of electrons become correlated, and thus become dependent on magnetic field. Although large positive magnetoresistance at room temperature has been achieved in metal-semiconductor hybrid devices (6-8), we have now realized it in a simpler structure and in a way different from other known magnetoresistive effects (9-14,20). It could be used to develop new magnetic devices from silicon, which may further advance silicon technology.

Microfabricated devices formed from alternating layers of magnetic and nonmagnetic materials at combined thicknesses of a few hundred nanometers exhibit a phenomenon known as the giant magnetoresistance effect. Devices based on this effect are known as giant magnetoresistive (GMR) sensors. The resistance of a GMR is dependent on the strength of an external magnetic field, which has resulted in the widespread usage of such platforms in high-speed, high-data density storage drives. The same attributes (i.e., sensitivity, small size, and speed) are also important embodiments of many types of bioanalytical sensors, pointing to an intriguing opportunity via an integration of GMR technology, magnetic labeling strategies, and biorecognition elements (e.g., antibodies). This paper describes the utilization of GMRs for the detection of streptavidin-coated magnetic particles that are selectively captured by biotinylated gold addresses on a 2 x 0.3 cm sample stick. A GMR sensor network reads the addresses on a sample stick in a manner that begins to emulate that of a 'card-swipe' system. This study also takes advantage of on-sample magnetic addresses that function as references for internal calibration of the GMR response and as a facile means to account for small variations in the gap between the sample stick and sensor. The magnetic particle surface coverage at the limit of detection was determined to be ~2%, which corresponds to ~800 binding events over the 200 x 200 pm capture address. These findings, along with the potential use of streptavidin-coated magnetic particles as a universal label for antigen detection in, for example, heterogeneous assays, are discussed.

This paper describes efforts aimed at setting the stage for the application of giant magnetoresistance sensor (GMRs) networks as readers for quantification of biolytes selectively captured and then labeled with superparamagnetic particles on a scanned chip-scale array. The novelty and long-range goal of this research draws from the potential development of a card-swipe instrument through which an array of micrometer-sized, magnetically tagged addresses (i.e., a sample stick) can be interrogated in a manner analogous to a credit card reader. This work describes the construction and testing of a first-generation instrument that uses a GMR sensor network to read the response of a 'simulated' sample stick. The glass sample stick is composed of 20-nm-thick films of permalloy that have square or rectangular lateral footprints of up to a few hundred micrometers. Experiments were carded out to gain a fundamental understanding of the dependence of the GMR response on the separation between, and planarity of, the scanned sample stick and sensor. Results showed that the complex interplay between these experimentally controllable variables strongly affect the shape and magnitude of the observed signal and, ultimately, the limit of detection. This study also assessed the merits of using on-sample standards as internal references as a facile means to account for small variations in the gap between the sample stick and sensor. These findings were then analyzed to determine various analytical figures of merit (e.g., limit of detection in terms of the amount of magnetizable material on each address) for this readout strategy. An in-depth description of the first-generation test equipment is presented, along with a brief discussion of the potential widespread applicability of the concept.

This paper applies nonequilibrium thermodynamics in the linear regime to describe spin diffusion and magnetoresistance effects and to examine the effect of spin mixing on transport through collinear magnetic layers. To demonstrate the method, it treats analytically the spin injection into a thick single ferromagnetic layer and through a spin valve. Index Terms--Magnetoresistance, Onsager matrix, spin-dependent transport, spin mixing, thermodynamics.

In this article, we review the insulator metal transition and the colossal magnetoresistance effect in manganites. The relevance of electro--lattice coupling and the resulting Jahn--Teller polaron is elaborated. The general features of electronic phase separation, which results from disorder and strain effects, are discussed along with electron--lattice coupling effects. Although a comprehensive theory is still lacking that can account for all the intricate features of manganite physics, electronic-phase separation and electron--lattice coupling appear to capture the essence of the colossal magnetoresistance effect in manganites.

The magnetotransport properties of [La.sub.0.7][Ca.sub.0.3-x][Ag.sub.x]Mn[O.sub.3] (0

The current-in-plane giant magnetoresistive (GMR) trilayer readback sensor (CIP-3L), where only one permanent magnet at the back edge of the GMR stack is used to stabilize and bias a dual free layer system, is reviewed. Micromagnetic modeling is employed to show that the design has improved efficiency over abutted junction (ABJ) tunneling magnetoresistive (TMR) head designs. An experimental evaluation of how permanent magnet thickness (PM Th), interlayer exchange coupling (J), and stripe height impact the signal-to-noise ratio, symmetry, and stability of prototype CIP-3L heads is conducted. The study indicates that PM Th >400 nm, J < -0.8 erg/[cm.sup.2], and a read width to SH aspect ratio of 1:1 to 0.75:1, gives optimal transfer curve performance. A head gimbal assembly spinstand comparison on perpendicular recording media with best-in-class TMR readers shows that although the amplitude of the CIP-3L heads is lower (believed to be process related), the symmetry, stability, and most important, bit-error rate normalized to electrical write width and read width, are comparable. In addition, the CIP-3L design shows better linearity and low-frequency noise performance than TMR heads. The areal density performance of the best CIP-3L heads shows 195 Gb/[in.sup.2] recording capability and linear densities of 1100 kbpi. Index Terms--Abutted junction (AJ), areal density (AD), micromagnetic modeling, trilayer readback sensor.

A read sensor working in the toggle mode is presented. The free layer comprises a balanced synthetic--antiferromagnetic (SAF) multilayer. The magnetization of the free SAF layer is perpendicular to the air-bearing surface (ABS) when bias field is applied in the direction of the ABS. The magnetization of the reference layer is fixed to be parallel to the ABS instead of perpendicular as is the conventional case. The sensitivity of the toggle read sensor (for small track width) improves significantly compared to the conventional abutted junction bias type. For a toggle sensor with long height structure, performance in both the sensitivity and linearity has also been improved because increased sensor height can be used for the lower bias field. The lower bias field is also compatible with the small gap structure of an in-stack bias scheme. Simulation results also show that the thermal magnetic noise in the toggle sensor is much smaller than that in the conventional biased sensor. Experimental results for both the current-in-plane (CIP) and tunneling-magneto-resistive (TMR) sensors with toggle mode are consistent with our calculation results. Index Terms--Hard bias, read sensor, spin-flop, synthetic-ferromagnetic.

Tunneling magnetoresistive (TMR) heads have been observed to exhibit relatively large low-frequency noise. Observation in a saturating field reveals that a substantial part of this noise is of electrical origin. Two distinctly different electrical noise phenomena are observed: 1/f noise and random telegraph (RT) noise. 1/f noise appears in all heads, RT noise only in some. The magnitude of the noise tracks the device resistance and the electrical bias. Therefore, the question arises if it is caused by resistance fluctuations or by the electrical bias. To answer this question, the paper describes a measurement setup to determine the TMR device noise in thermodynamic equilibrium (no bias). It is concluded that at zero bias there is no electrical low-frequency noise; neither 1/f noise nor RT noise was detected. Further, the paper proposes an electroacoustic model for the origin of the 1/f noise and estimates the expected magnitude. For the RT noise, in addition to the well-known trapped charge blocking model, an electromigratory model is proposed to better cover all observed RT noise features. Index Terms--Low-frequency noise, noise modeling, 1/f noise, random telegraph noise, tunneling magnetoresistive noise

The magnetoresistance (MR) of the current-in-plane spin-valve, which is currently utilized as the readback sensor in the majority of hard disk drives, has reached a maximum MR of DR/[R.sub.min.] ~ 20% and D[R.sub.sheet] ~ 4 [OMEGA]/sq. A new sensor film stack will be introduced here that utilizes a trilayer (CoFe\Cu\CoFe), where the Cu interlayer is very thin (~10 [Angstrom].) to enhance the MR and where the Cu thickness is chosen such that the ferromagnetic Neel coupling and the antiferromagnetic Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling between the CoFe layers partially cancel one another, to maximize the sensitivity. By changing the Cu interlayer thickness, the overall interlayer coupling was adjusted from about -0.05 erg/[cm.sup.2] to -0.4 erg/[cm.sup.2] while keeping the MR large. Nano-oxide layers (NOLs) are also incorporated below and above the trilayer sensor to enhance the MR. An example of this sensor is NiFeCr 20 [Angstrom]/CoFeO 10 [Angstrom]/CoFe 15 [Angstrom]/Cu 10.5 [Angstrom]/CoFe 15 [Angstrom]/AIO 30 [Angstrom] and will be referred to as CIP-3L. With the combination of the thin Cu spacer, the NOLs and minimal additional layers to shunt the current around the trilayer sensor (no antiferromagnetic material and no pinned layers), as deposited sheet films with an MR of DR/R > 25 % and DR/sq. > 20 [OMEGA]/sq, were achieved. This paper shows the optimization of the sensor stack, such as film thicknesses, NOL material, and oxidation process, the adjustability of the interlayer exchange coupling between the CoFe layers and also shows the repeatability of the sensor deposition. Index Terms--Current-in-plane (CIP), giant magnetoresistance (GMR), magnetoresistance (MR), magnetic recording.

Using the semiclassical Boltzmann theory, we have investigated the influences of pure interface, nonpure interface, bulk, and interface plus bulk scattering on the giant magnetoresistance (GMR) dependence on layer thickness of the bottom spin valve (BSV), synthetic antiferromagnetic (SAF) spin valve, and dual spin valve (DSV). Our work shows consistency with experiment and theory and may provide some useful guidelines for electrical and structural optimizations of spin valves. Index Terms--Boltzmann equation, magnetoresistance, scattering, spin valve.

The giant magnetoresistive (GMR) head used in magnetic recording is an extremely sensitive device that is sensitive to electrostatic discharge (ESD). A generally available coated wire that is electrified on its surface can increase the potential of the copper core. When the wire is touched to the GMR head terminal, the discharge current can damage the sensor of the GMR head. Four types of wires were measured for three lengths each. Resincoated wires were electrified from 20 V to more than 1 kV. The peak current discharging to the GMR head ranged from 100 mA to more than 1000 mA. A resin-coated wire as short as 5 cm was found to damage the GMR head. Among the wires examined herein, only the enameled wire is recommended to connect the GMR head because no charge or discharge currents were observed for this wire. When an ionizer is used to neutralize the tribocharge on the surface of the wire, the remaining charge in the copper core depends on the effectiveness of the neutralization process. A wire with an antistatic coating is required in order to reduce the ESD threat to sensitive devices such as the GMR head. Index Terms--Charge transfer, coated wire, electrostatic voltage, giant magnetoresistive (GMR) head.

We report the first demonstration of a magnetoresistive random access memory (MRAM) circuit incorporating MgO-based magnetic tunnel junction (MTJ) material for higher performance. We compare our results to those of AlOx-based devices, and we discuss the MTJ process optimization and material changes that made the demonstration possible. We present data on key MTJ material attributes for different oxidation processes and free-layer alloys, including resistance distributions, bias dependence, free-layer magnetic properties, interlayer coupling, breakdown voltage, and thermal endurance. A tunneling magnetoresistance (TMR) greater than 230% was achieved with CoFeB free layers and greater than 85% with NiFe free layers. Although the TMR with NiFe is at the low end of our MgO comparison, even this MTJ material enables faster access times, since its TMR is almost double that of a similar structure with an Al[O.sub.x] barrier. Bit-to-bit resistance distributions are somewhat wider for MgO barriers, with sigma about 1.5% compared to about 0.9% for Al[O.sub.x]. The read access time of our 4 Mb toggle MRAM circuit was reduced from 21 ns with Al[O.sub.x] to a circuit-limited 17 ns with MgO. Index Terms--MgO, magnetic random access memory (MRAM), magnetic tunnel junction (MTJ), toggle switching, tunneling magnetoresistance (TMR).

We have fabricated pseudo-spin-valve (PSV) multilayers with amorphous CoNbZr alloy as a soft magnetic layer and a buffer layer by magnetron sputtering. We investigated the multilayers' giant magnetoresistanee (GMR), microstructure, thermal annealing effects, and application characteristics. Our results show that the film microstructure, consequently the magnetostatic coupling effect and the magnetization reversal process, strongly depends on the CoNbZr thickness. We observed antiparallel magnetization alignments in the samples with a 2-4 nm CoNbZr layer and a measured maximum GMR ratio of 6.5%. The PSV with 4 nm CoNbZr has a superior thermal stability to 4110 [degrees] C as a result of the dense and homogeneous Cu spacer. After patterning with a 6 [micro]m x 1 [micro]m elliptic stripe, the structure forms a single domain. The dynamic GMR behavior under a 10 kHz sinusoidal magnetic field indicates the patterned stripe has a linear and stable GMR response. We therefore believe that PSVs with amorphous CoNbZr have good potential for spintronic devices. Index Terms--Amorphous magnetic films, giant magnetoresistance, pseudo-spin-valve.

A low field (H=0.5 T) magnetoresistance of colossal magnetoresistive (CMR) composites prepared with ferromagnetic (FM)- antiferromagnetic (AFM) couples system (100-x) La0.7Pb0.3MnO3 (LPMO)+xPr0.63Ca0.37MnO3 with x=0-85 wt % is reported. It is concluded that the (100-x) LPMO= x PCMO type FM-AFM composites are prepared by solid state ceramic route.

The playback characteristics of common magnetoresistive heads applied in magnetic recording systems are examined based on bit-patterned medium. The results reveal that analytical solution for a pointlike reader is used to elucidate the playback resolution limits for given patterned medium morphology.

The influence in the I-V characteristics and tunnel magnetoresistance (TMR) of impurities embedded into the insulating barrier separating the two ferromagnetic electrodes of a magnetic tunnel junction was theoretically investigated. When the energy of the electron bound state at the impurity site is close to the Fermi energy, the current and TMR are strongly enhanced in the vicinity of the impurity.

Thin structures of alternating magnetic and nonmagnetic layers with a total thickness of a few hundred nanometers exhibit a phenomenon known as giant magnetoresistance. The resistance of microfabricated giant magnetoresistors (GMRs) is dependent on the strength of an external magnetic field. This paper examines magnetic labeling methodologies and surface derivatization approaches based on protein-protein binding that are aimed at forming a general set of protocols to move GMR concepts into the bioanalytical arena. As such, GMRs have been used to observe and quantify the immunological interaction between surface-bound mouse IgG and [alpha]-mouse IgG coated on superparamagnetic particles. Results show the response of a GMR network connected together as a set of two sense GMRs and two reference GMRs in a Wheatstone bridge as a means to compensate for temperature effects. The response can be readily correlated to the amount of the magnetically labeled [alpha]-mouse IgG that is captured by an immobilized layer of mouse IgG, the presence of which is confirmed with X-ray photoelectron spectroscopy and atomic force microscopy. These results, along with a detailed description of the experimental testing platform, are described in terms of sensitivity, detection limits, and potential for multiplexing.

Current-perpendicular-to-plane (CPP) giant magnetoresistive (GMR) read heads and wraparound shielded write heads for perpendicular recording were fabricated, and their recording performance was tested. The measured readout waveform of the CPP-GMR head was noise free and well biased. An output voltage of 2.2 mV and head-amp signal-to-noise ratio (SNR) of 30 dB were obtained from an operating voltage of 120 mV. Thermal damage in the heads was caused by an increase in the area of pinholes. The activation energy for the 5% resistance reduction was estimated to be 2.3 eV, which was similar to the self-diffusion energy of Co. The lifetime of the heads was projected to be 200 years. Newly developed CPP-GMR films showed the MR ratio of 6% at the resistance area product of 0.3 [OMEGA][micro][m.sup.2]. The wraparound shielded write heads showed similar overwrite values to that of the unshielded heads. The shielded heads showed about 1 dB better media SNR and 5%-10% better linear resolution than the unshielded heads. Smaller side writing was found in the wraparound shield design, when the half-width of the off-track profile was the same. Better down-track and cross-track performance was thought to be due to a tighter field distribution in the shielded heads. Index Terms--Activation energy, current-perpendicular-to-plane (CPP)-giant magnetoresistive (GMR), perpendicular recording, reliability, wraparound shield.

The orbital ordering in a three-dimensional colossal magnetoresistance manganite, namely La(sub 7/8)Sr(sub 1/8)MnO3 is investigated by applying soft X-ray linear dichroism to the Mn L edge. It is found that the cooperative Jahn-Teller distorted orthorhombic phase, which is present at a temperature of 240 K, is probably accompanied by a predominantly cross type (x(super 2)-z(super 2))/(y(super 2)-z(super 2)) orbital ordering.

The mechanisms involved in the change in magnetoresistance (MR) as a pseudo spin valve (PSV) of the form NiFe/Cu/NiFe is patterned into a nanowire array. In situ measurements were used to investigate the change in the performance of the PSV for different milling depths and wire widths.

The magnetoresistance (MR) of spin valves is investigated by varying the strength of the field applied in a fixed direction and by rotating the field with fixed strength. The resulting MR curves are fitted with a single domain model to determine with high precision the exchange bias field, the unaxial anisotropies, the giant magnetoresistance ratio, and the interlayer-coupling field.

The existence of a ballistic magnetoresistance (BMR) effect in magnetic nanocontacts is examined. The thin film and thin wire geometries for both mechanically formed and electrodeposited nanocontacts show no indication of BMR and the observed magnetoresistance (MR) is less than 0.4 percent.

The annealing effects on magentoresistance (MR) values for the top and bottom spin valves are examined. The MR value of bottom spin valves declines with the increase in annealing temperature and disappears at the blocking temperature of 200 degrees C whereas the MR value of the top valves rises to the maximum at the annealing temperature of 100 degrees C and then decline with the further increase in the annealing temperature to about 250 degrees C.

Spin transfer effect in spin-valve pillars developed for current-perpendicular-to-plane (CPP) magnetoresistive heads is examined. The spin transfer acts as an effective field at low current resulting in current dependent loop shift of the free layer and inverted coercivity effects.

In this article magnetostrictive and piezoelectric laminate composites have been studied. The results demonstrate that the longitudinal-transverse magnetoelectric (ME) mode has dramatically higher ME coefficients than the transverse-transverse modes.

Magnetoresistance and magnetic hysteresis loop measurements have been used to investigate the strong interfacial coupling in cobalt oxide/ferromagnet bilayers at low temperatures, in this study. For the biased state, an asymmetry in the magnetization reversal processes has been found.

Electron mobility of two-dimensional electron gas (2-DEG) at the AlGaN/GaN interface is investigated and reported.

The authors present experiments and discuss recent results on ballistic magnetotesistance in nanometer size (on the order of 1 to 10 nm) nanocontacts grown by electrodeposition in thin wires and in thin films of a few nanometer thickness. Very large values of magnetoresistance are shown (up to 4000% and more could be obtained). These experiments as well as others are explained in terms of a dead magnetic layer appearing at the nanocontact. The experiments are also discussed in the context of magnetostriction effects, in the light of existing first principle calculations and observed inverse magnetoresistive effects. Index Terms--Electrodeposition, magnetoresistance, magnetostriction, nanocontact.

The authors present various new phenomena in magnetic tunneling junction (MTJ). Since the interface and barrier structure play a significant role in determining the physical phenomena, they have employed various techniques to characterize this structure. For obtaining the barrier information, they have performed electron holography studies which directly show the energy profile with atomic resolution. The interdiffusion between different layers has been studied using high-resolution transmission electron microscopy, elemental mapping, and time-of-flight secondary ion mass spectrometry, With this structural information, the authors showed the existence of bulk. like contribution in MTJ and determined the characteristic length. In addition, they also observed a conductance minimum anomaly which is much different from the normally observed zero bias anomaly. Large inversed TMR has also been observed at bias as high as 0.4 V in MTJs with an [Al.sub.2][O.sub.3]-ZrO barrier. The authors have modified the Brinkman model by incorporating the voltage dependent density of states of the ferromagnetic electrodes, which sucessfully explains the bias dependence of the tunneling magnetoresistance (TMR), conductance minimum anomaly, and inversed TMR. Index Terms--Electron holography, magnetic tunneling junction (MTJ), tunneling magnetoresistance (TMR) bias dependence.

Magnetoresistance (MR) of current-perpendicular spin valves with nano-oxide layers (NOLs) has been investigated. Insertion of a NOL in a spacer between free and pinned magnetic layers can increase both resistance and MR ratio of the spin valves to the level that satisfies the needs for over 150-Gb/[in.sup.2] recording density. It is shown that the MR enhancement is strongly NOL-material dependent; ferromagnetic CoFe(B) alloys are found to be quite effective in the improvement, while nonmagnetic composites such as TaCu and RuCu degrade the MR ratio. The NOL-thickness dependence of the MR ratio is also measured. It is presented that the CoFe(B) NOL thicker than 1 nm greatly enhances the MR ratio. Nominal-thickness dependence of residual magnetic moment of the NOLs shows that partially oxidized CoFe(B) layers are most effective for the MR enhancement. Little degradation of the free-layer response to an applied magnetic field by the NOL insertion has been observed. From the current-voltage (I-V) characteristic, the electronic transport is revealed to be dominated by metallic conduction rather than tunneling. It suggests that the enhancement stems from the conduction through pinholes. Index Terms--Current perpendicular to plane, giant magnetoresistive heads, oxide layers, spin-valve structures.

We used Kerr microscopy to investigate the magnetization processes of NiFe--Co/Cu/Co/FeMn spin-valve meanders for magnetoresistive sensors and compared them to processes in related single films and bilayers. We observed irregular switching, characterized by the irreversible decay of blocked domains or by domain nucleation at 360[degrees] walls, in the related films and in the free layer of the spin-valve system. Both effects are connected with hysteresis. Edge-curling walls are responsible for rotational hysteresis in the giant magnetoresistance signal of the spin valves, occurring during field rotation in clockwise and counterclockwise directions. The U-turns of the meanders and their shape have no relevant influence on the magnetization behavior and hysteresis effects. Index Terms--Giant magnetoresistance (GMR), magnetic domains, magnetic multilayers, magnetic sensors, magnetization process, spin valves.

We have developed a readback equalizer for a perpendicular magnetic disk with a commercial anisotropic magnetoresistive head for use with a PR4ML read channel with 8-9 coding. The transfer function of the perpendicular magnetic disk, derived by Fourier analysis, has a phase lag of 90[degrees] from that of the longitudinal magnetic disk. We defined the parameters of the equalizer by simulation. The equalized readback signal nearly satisfied Nyquist's first criterion. Using resistor-capacitor circuits that correspond to the simulated function, we obtained a byte-error rate of below [10.sup.-7] Comparing the effect of incorporating PR4 or PR1 as part of the equalizer, we observed that PR4 gave a lower bit-error rate than PR1. Thus, PR4 is an effective detection method for a perpendicular magnetic disk. It is suitable not only for longitudinal magnetic disks, but also for perpendicular magnetic disks. Index Terms--Byte-error rate (BER), 8-9 coding, equalizer, Fourier analysis, magnetoresistive (MR) head, perpendicular magnetic disk, phase, PR4ML, pseudodifferential circuit, RC circuit.

Magnetization dynamic equations with thermal fluctuations are derived fundamentally for small amplitude oscillations. A tensor form of phenomenological damping occurs whose components reflect a general elliptical magnetization motion. This analysis implies that thermal energy and associated damping must be applied to independent normal modes of the system. As an example, this formulism is applied to a thin film magnetoresistance sensor to find the eigenmodes for general nonuniform magnetization variations. Examples are given of both the various modes and the noise power spectra. Index Terms--Damping parameter, magnetoresistance noise, mode analysis, thermal fluctuations.

Magnetoresistance (MGR) effect of p-type semi conducting diamond films was studied. Effect on the disk structure was greater than on the strip sample.

The room temperature extraordinary magnetoresistance (EMR) of a mesoscopic sensor structure prepared from an InSb quantum well of dimension 30 nm wide x 100 nm high x 3 [micro]m long is reported. The observed EMR is 4.75% at a relevant field of 0.05 T. The advantages and disadvantages of this nonmagnetic composite semiconductor/metal structure relative to that of conventional magnetic giant magnetoresistance (GMR) and tunneling magnetoresistance (TMR) devices for use as read-heads in high-density magnetic recording are discussed. Index Terms--Extraordinary magnetoresistance, inhomogeneities, InSb, nonmagnetic narrow-gap semiconductors.

Tunnel giant magnetoresistance (TMR) heads at ~50 Gb/[in.sup.2] have been fabricated using improved lapping process. Together with writer of 2.0 T pole materials, recording performance has been demonstrated at magnetic write width of 0.28 [micro]m and magnetic read width of 0.18 [micro]m. The resistance area product of final wafer data is around 5 [OMEGA] * [micro][m.sup.2], with lead and contact resistance included, resulting in a final head resistance of around 200 [OMEGA]. The output voltage achieved for 1 mA bias current is 42 mV/[micro]m, and the isolated pulses are stable. With a discrete preamplifier, the track density as measured by '747 curve' is 94 kTPI at a bit-error rate of [10.sup.-4] and the linear density is 508 kBPI, achieving an areal density of 48 Gb/[in.sup.2]. The noise analysis reveals that the noises come mainly from media and shot noise. Index Terms--CPP geometry, electric properties, magnetic tunnel junction, shot noise, TMR head, tunnel GMR.

Thermal magnetization fluctuations (mag-noise) in giant magnetoresistive (GMR) spin valve (or any MR) heads will serve as a fundamental limit on their signal-to-noise-ratio (SNR). Measured mag-noise in several varied spin-valve read sensors is shown to be in good quantitative agreement with predictions based on the fluctuation-dissipation theorem. The dependence of magnoise and head-SNR on sensor geometry and other device parametrics is discussed. Index Terms--Magnetic heads, magnetic noise, magnetic recording, magnetoresistive devices.

Experimental measurements and theoretical analysis of giant magnetoresistive (GMR) thermal magnetization fluctuation noise are presented. A new form of tensor damping, characteristic of the anisotropic thin-film geometry, is utilized. Rationalization and experimental confirmation for this expanded form are given as well. In general, this noise is inversely proportional to the sensor volume and, at frequencies less than the sensor ferromagnetic resonance (FMR), is proportional to the dynamic damping. Approximate crosstrack anisotropy and stabilization fields are determined from signal transfer curves and utilized to determine damping for each head sensor. Damping parameters do not vary appreciably, although variation is seen even within a given manufacturing batch. Index Terms--Dynamic damping constants, GMR heads, magnetization noise spectra, thermal fluctuations.

Complementary metal-oxide semiconductor (CMOS) Magnetotransistor (MT) offset is experimentally characterized. Its causes are analyzed for two commercial CMOS processes.

A new method for recording above 100 Gb/in (super 2) is discussed. This method is called 'hybrid recording', a form of thermally assisted recording that combines thermo-magnetic writing and magnetic reading.