Giant Magnetoresistance Spin Valves Research Articles

Suppression of spin torque noise in current perpendicular to the plane spin-valves by addition of Dy cap layers

We demonstrate that the addition of Dy capping layers in current perpendicular to the plane giant magnetoresistive spin-valves can increase the critical current density beyond which spin-torque induced instabilities are observed by about a factor of three. While Dy capped samples exhibit nonmagnetic 1/f noise, it is sufficiently small to be unimportant for read head operation at practical data rates.

Thermally induced structural transformation in Co films for giant magnetoresistance spin valves

Thermally induced structural transformation in Co films for giant magnetoresistance spin valves

Diffusion based degradation mechanisms in giant magnetoresistive spin valves

Spin valve systems based on the giant magnetoresistive effect as used, for example, in hard disks and automotive applications consist of several functional metallic thin film layers. We have identified by secondary ion mass spectrometry two main degradation mechanisms: one is related to oxygen diffusion through a protective cap layer and the other one is interdiffusion directly at the functional layers of the giant magnetoresistive stack. By choosing a suitable material as cap layer (TaN), the oxidation effect can be suppressed.

Advances in Giant Magnetoresistance Biosensors With Magnetic Nanoparticle Tags: Review and Outlook

We present a review of giant magnetoresistance (GMR) spin valve sensors designed for detection of magnetic nanoparticles as biomolecular labels (nanotags) in magneto-nano biodetection technology. We discuss the intricacy of magneto-nano biosensor design and show that as few as approximately 14 monodisperse 16-nm superparamagnetic nanoparticles can be detected by submicron spin valve sensors at room temperature without resorting to lock-in (narrow band) detection. GMR biosensors and biochips have been successfully applied to the detection of biological events in the form of both protein and DNA assays with great speed, sensitivity, selectivity, and economy. The limit of molecular detection is well below 10 pM in concentration, and the protein or DNA assay time can be under two hours. The technology is highly scalable to deep multiplex detection of biomarkers in a complex disease, and amenable to integration of microfluidics and CMOS electronics for portable applications. On-chip CMOS circuitry makes a sensor density of 0.1-1 million sensors per square centimeter feasible and affordable. The theoretical and experimental results thus far suggest that magneto-nano biochip-based GMR sensor arrays and nanotags hold great promise in biomedicine, particularly for point-of-care molecular diagnostics of cancer, infectious diseases, radiation injury, cardiac diseases, and other diseases.

Thermal stability of synthetic antiferromagnet and hard magnet coupled spin valves

The magnetic properties of current-in-plane (CIP) giant magnetoresistive (GMR) spin valves employing synthetic antiferromagnet (SAF) pinning have been investigated. The conventional spin valve structure, with a ferromagnetic (FM) layer pinned by an antiferromagnet (AFM) layer, exhibits high electrical resistance, the AFM typically being a high resistivity material. We have investigated pinning with a Co∕Ru∕Co SAF trilayer only, with no additional AFM pinning. We have also investigated spin valves employing a hard magnet layer in three different configurations as the pinning/pinned layer. Elimination of the AFM-induced parasitic resistance has the potential for yielding a higher GMR ratio in current-perpendicular-to-the-plane (CPP) structures. The full-film properties have been optimized by using vibrating sample magnetometry and CIP magnetotransport measurements. The thermal stability of SAF-pinned spin valves and hard magnet-pinned spin valves has been characterized through magnetotransport measurements of up to 400K, and found to have measurable MR even at that temperature. A study of the M-H loops for the SAF spin valve showed no change up to 500K. Therefore, these non-AFM-containing spin valves appear to be usable in CPP devices under practical head operating temperatures, representing a significant advance in reduced stack resistance, increased MR ratio, and reduced coupling between free and pinned layers in a small-dimensional patterned structure.

Detection of Magnetic Nanoparticles and Fe-hemoglobin inside Red Blood Cells by Using a Highly Sensitive Spin Valve Device

A highly sensitive, giant magnetoresistance-spin valve (GMR-SV) biosensing device with high linearity and very low hysteresis was fabricated by photolithography. The detection of magnetic nanoparticles and Fe-hemoglobin inside red blood cells using the GMR-SV biosensing device was investigated. When a sensing current of 1 mA was applied to the current electrode in the patterned active devices with an area of <TEX>$2{\times}6{\mu}m^2$</TEX>, the output signals were about 13.35 mV. The signal from even one drop of human blood and nanoparticles in distilled water was sufficient for their detection and analysis.

Effects of gas-cluster ion beam processing on physical, magnetic, and giant magnetoresistance properties of α-Fe 2O 3 bottom spin-valves

The effects of gas-cluster ion beam (GCIB) processing accelerated by a few thousands of volts on the surface roughness, crystalline orientation texture, magnetic, and giant magnetoresistance (GMR) properties of exchange biased α-Fe 2O 3 bottom spin-valves have been investigated. It was found that all of these properties were strongly influenced by the GCIB processing conditions, such as gas sources including Ar, H 2, O 2, and their mixture combinations, and ion cluster doses. The properties of both GCIB processed and unprocessed areas on 50 and 100-nm thick α-Fe 2O 3 coated Si(1 0 0) wafers with GMR multi-layers of Co(3)/Cu(2.5)/Co(3)/Ta 2O 5(2.5 nm) were compared. The GMR ratio, Δ R/ R 0, was consistently increased by up to 20–30% for the areas that were GCIB processed with condition “P1(10 14 Ar gas)+P4(5×10 14 Ar+H 2 gases) ion cluster ions/cm 2” (Δ R/ R 0=14%) over the unprocessed α-Fe 2O 3 layer (Δ R/ R 0=11.2%), and decreased by up to 80% when using the process with the heaviest ion does, “P3” (Δ R/ R 0=2.4%). In addition, GCIB processing changed the magnetic properties of GMR spin-valve including exchange bias field, pinned, and free-layer coercivities significantly. The free-layer coercivity was decreased dramatically with “P1+P4” GCIB processing from 160 Oe to as low as 27 Oe and the exchange bias field increased from 72 Oe up to ∼125 Oe. The decrease of the GMR ratio, pinned coercivity, and exchange bias field when the “P3” condition process was used are thought to be due to surface damage and composition changes of the α-Fe 2O 3 anti-ferromagnetic layer. X-ray photoelectron spectroscopy (XPS) analysis of the α-Fe 2O 3 thin film surface showed a 4.6% reduction of the oxygen content (unprocessed: 65 kcps (kilo-counter per second), “P3”: 62 kcps) after application of the P3, the heaviest process condition. Atomic force microscopy (AFM), X-ray diffraction (XRD), and cross-sectional transmission electron microscopy (XTEM) analyses suggest that the increase of the GMR ratio and the improved magnetic properties of optimized GCIB-processed α-Fe 2O 3 spin-valve are due to the reduction of surface roughness and improvement of the crystalline orientation texture resulting from a more “defect-free” or denser α-Fe 2O 3 layer.

保護層材料による層間交換結合型スピンバルブＧＭＲ膜の耐熱性向上

Interlayer-exchange-coupled (IEC) type spin-valve giant magnetoresistive (SVGMR) films in which the pinning layer does not contain an anti-ferromagnetic layer have been investigated. The IEC-type SVGMR films had good SV properties with a 10% MR ratio as deposited. However, the MR ratio decreased with increasing annealing temperatures over 310°C. From cross sectional TEM observation, interfacial roughness between the free and pinned layers was increased by annealing, and such roughness causes the degradation of SVGMR properties. Thermal stability of SVGMR films was improved when the thickness of Ta capping layer was 5 nm. In order to reduce the thickness of capping layer, various materials of Ru, Cu, and NiFeCr were investigated instead of Ta. No degradation in SV properties after 320°C annealing was achieved with the 2 nm of Ru capping layer.

Effect of dual-synthetic antiferromagnet structre on giant magnetoresistance in spin valves

The properties of dual-synthetic antiferromagnet (DSAF) structure Co90Fe10(5 nm)/Ru(x nm)/Co90Fe10(3 nm)/Ru(y nm)/Co90Fe10(5 nm) (in which x=0.45 y=0.45; x=0.45 y=1; x=1, y=1) were studied. The effect of DSAF structure on giant magnetoresistance (GMR) single spin-valve (SPV) structures was also studied. The study shows that the properties of DSAF are better than those of the conventional synthetic antiferromagnet Co90Fe10(5 nm)/Ru(0.5 nm)/Co90Fe10(3 nm). We demonstrated that the DSAF structure as a pinned layer dramatically enhances the GMR ratio in single SPV films at room temperature.

Estimation of Density of Low-Concentration Magnetic Fluid by a Needle-Type GMR Sensor for Medical Applications

The size, shape and composition of magnetic nanoparticles make it an attractive tool in medical applications. Low concentration Dextran Magnetite (DM)® or magnetic fluid is widely used for biomedical applications. This paper reports experimental apparatus designed for testing low concentration magnetic fluid, results obtained by experimentation utilizing a simple, novel and low invasive needle-type spin-valve giant magnetoresistance (SV-GMR) sensor and numerical analysis for comparison with the experimental results obtained. Low concentration magnetic fluid weight density is estimated by the difference between the magnetic flux density inside and outside a magnetic fluid filled cavity. The results show that the proposed technique employing the needle sensor has a good potential to be used in biomedical applications such as hyperthermia therapy in cancer treatment and targeted drug delivery, for low concentration magnetic fluid weight density measurements in-vivo.

ＣＣＰ‐ＮＯＬを有するＣＰＰ‐ＧＭＲ膜のＭＲ変化率とナノ微細構造の関係

Current-Perpendicular-to-Plane Giant MagnetoResistance (CPP-GMR) spin valves with a Current-Confined-Path (CCP) Nano-Oxide Layer (NOL) were investigated from the viewpoint of the relation between MR ratio and nanostructure. We have reported that the CPP-GMR spin valves with the CCP-NOL fabricated by Ion-Assisted Oxidation (IAO) show higher MR ratio than those fabricated by Natural Oxidation (NO). In this report, the nanostructures of CPP-GMR spin valves are compared by means of the high-resolution Transmission Electron Microscope (TEM) and the Fast Fourier Transform (FFT) map. It was confirmed that IAO is effective for improving the crystalline structure not only for the CCP, but also for the free layer on the CCP. The well crystalline structure can decrease the resistivity of the metal path and enhance the spin-dependent scattering inside the free layer, which are considered to be the reasons for the enhancement of MR ratio for the IAO.

磁気センサを利用した丸棒鋼用アレイ渦流探傷技術の基礎開発

Eddy current probe to detect longitudinal discontinuities such as seams of wires and bars has been discussed. Conventional encircling coil is hard to detect the longitudinal discontinuities because of the fundamental principal restriction. Moreover, a system using a rotating probe hardly has an ability to support high-speed inspection. Therefore, a probe with array sensors has been developed to detect the longitudinal discontinuities without mechanical rotor. The spin-valve type giant magnetoresistance (SV-GMR) sensor was used as the detection sensor. It has advantages in high sensitivity, high frequency response characteristic up to 100 MHz, and the integration of the sensor element compared with coil or other magnetic sensors. The probe is constructed from two excitation coils and 36 detection sensors. The excitation coils are encircling type such as the conventional encircling coils and excited by opposite phase each other. The detection sensors are arranged in the directions of surrounding a rod for examination between excitation coils. The probe has the capabilities to detect the longitudinal notches by sequential scanning with detection sensors. In addition, a correction method for eccentric effect is proposed by taking the addition of signals at position of opposed sensor pair. The present study showed that the probe has the ability to detect the longitudinal notch that depth of 0.3 mm with 5 mm air gap.

An SV-GMR Needle Sensor-Based Estimation of Volume Density of Magnetic Fluid inside Human Body

A spin-valve giant magneto-resistive (SV-GMR) sensor of needle-type configuration is reported to estimate the volume density of magnetic fluid inside human body. The magnetic fluid is usually injected into human body to kill cancerous cell using hyperthermia-based treatment. To control the heat treatment, a good knowledge of temperature is very much essential. The SV-GMR-based needle-type sensor is used to measure the magnetic flux density of the magnetic fluid inside the human body from which the temperature is estimated. The needle-type sensor provides a semi-invasive approach of temperature determination.

Effect of pinholes in magnetic tunnel junctions

The electron transport in magnetic tunnel junction containing pinholes is studied, where ferromagnetic layers make direct contact through narrow conducting channels. The transport is treated within the Landauer formalism using a tight-binding Hamiltonian. It is found that a narrow pinhole induces a resonant tunneling behavior causing a magnetoresistance that oscillates with the bias voltage. After averaging over pinholes of various shapes, the oscillation and magnitude of magnetoresistance (MR) are reduced, which can explain how barrier roughness diminishes the MR. For a pinhole of a large radius, where the number of atoms inside is much larger than 1, an enhanced MR is obtained whose value is similar to an all-metal giant magnetoresistance spin valve.

센서용 거대자기저항 스핀밸브소자의 열처리 효과

셀(cell) 단위의 생체분자의 자성특성 검출을 위한 거대자기저항-스핀밸브(giant magnetoresistance-spin valves; GMR-SV) 바이오센서로서 미세 패턴된 모양에 따라 길이 방향과 폭 방향 용이축에 의존하는 자기저항 특성을 연구하였다. 바이오센서(biosensor)로서 사용할 스핀밸브 다층구조는 glass/NiO/NiFe/CoFe/Cu/CoFe/NiFe 이었다. 자성 다층박막의 일축이방성을 만들기 위해 증착시와 소자 패턴닝 후 진공 열처리를 <TEX>$200^{\circ}C$</TEX>에서 300 Oe 정도 외부자기장을 인가하였다. 형상자기이방성 효과를 고려하여 광 리소그래피 과정으로 얻은 미세 활성영역 패턴 사이즈는 <TEX>$2{\times}5{\mu}m^2$</TEX>로 정하였다. 2단자법으로 길이방향의 센싱전류와 폭 방향의 고정층의 용이축 방향 각도에 의존하는 자장민감도의 변화는 바이오센서 소자로서 활용에 중요한 요인임을 확인하였다. In order to detect of the magnetic property in the cell unit, we studied the GMR-SV (giant magnetoresistance-spin valves) biosensor, which was depended on the micro patterned features according to two easy directions of longitudinal and transversal axes. Here, the multi layer structure was glass/NiO/NiFe/CoFe/Cu/CoFe/NiFe. The uniaxial anisotropy direction was applied to the patterned biosensor during the deposition and vacuum post-annealing at <TEX>$200^{\circ}C$</TEX> under the magnitude of 300 Oe, respectively. Considering the magnetic shape anisotropy effect, the size of micro patterned biosensor was a <TEX>$2{\times}5{\mu}m^2$</TEX> after the photo lithography process. By our experimental results, we confirmed that the best condition of GMR-SV biosensor should be the same direction of the axis sensing current and the easy axis of pinned NiO/NiFe/CoFe triple layer oriented to the width direction of device, and the direction of the easy axis of free CoFe/NiFe bilayer was according to the longitudinal direction of device.

어레이 IrMn 스핀밸브 소자의 자기저항특성 연구

어레이(away) 자성센서 개발을 위해 고진공 스퍼터링 증착장비를 이용하여 스펙큘러형(specular type) Glass/Ta(5)/NiFe(7)/IrMn(10)/NiFe(5)/<TEX>$O_2$</TEX>/CoFe(5)/Cu(2.6)/CoFe(5)/<TEX>$O_2$</TEX>/NiFe(7)/Ta(5)(nm) 거대자기저항-스핀밸브(giant magnetoresistive-spin valves; CMR-SV)박막을 제작하였다. 다층박막 시료를 <TEX>$20{\times}80{\mu}m^2$</TEX>의 미세 활성영역을 가진 15개 어레이를 <TEX>$8{\times}8mm^2$</TEX> 영역 내에 최적화한 제작 조건으로 광 리소그래피 패터닝 하였다. Cu를 증착하여 만든 2단자 전극법으로 측정한 자성특성은 15개 모든 소자들이 균일한 자기저항특성을 나타내었고, 5 Oe 근방에서 가장 민감한 자기저항비 자장민감도와 출력전압들은 각각 0.5%/Oe, <TEX>${\triangle}$</TEX>V: 3.9 mV이었다. 형상자기이방성이 적용된 상부 자유층 <TEX>$CoFe/O_2/NiFe$</TEX>층은 하부 고정 자성층 <TEX>$IrMn/NiFe/O_2/CoFe$</TEX>층 자화 용이축과 직교하였다. 측정시 인가전류 값을 각각 1 mA에서 10 mA까지 인가하였을 때 출력 작동 전압 값은 균일하게 증가하였으며, 자장감응도도 거의 일정하여 미세 외부자장에 민감한 나노자성소자로서 좋은 특성을 띠었다. To develop array magnetic sensors, specular-type giant magnetoresistive- spin valve (GMR-SV) film of Glass/Ta(5)MiFe(7)/IrMn(10)NiFe(5)/<TEX>$O_2$</TEX>/CoFe(5)/Cu(2.6)/CoFe(5)/<TEX>$O_2$</TEX>/NiFe(7)/Ta(5)(nm) was deposited by using a high-vacuum sputtering system. One of 15 way sensors in the area of <TEX>$8{\times}8mm^2$</TEX> was Patterned a size of <TEX>$20{\times}80{\mu}m^2$</TEX> in multilayer sample by Photo-lithography. All of 15 sensors with Cu electrodes were measured a uniform magnetic properties by 2-probe method. The highest magnetic sensitivity of MR and output voltage measured nearby an external magnetic field of 5 Oe were MS = 0.5%/Oe and <TEX>${\triangle}$</TEX>V= 3.0 mV, respectively. An easy-axis of top-free layers of <TEX>$CoFe/O_2/NiFe$</TEX> with shape anisotropy was perpendicular to one of bottom-pinned layers <TEX>$IrMn/NiFe/O_2/CoFe$</TEX>. When the sensing current increased from 1 mA to 10 mA, the output working voltage uniformly increased and the magnetic sensitivity was almost stable to use the nano-magnetic devices with good sensitive properties.

Template-Grown NiFe/Cu/NiFe Nanowires for Spin Transfer Devices

We have developed a new reliable method combining template synthesis and nanolithography-based contacting technique to elaborate current perpendicular-to-plane giant magnetoresistance spin valve nanowires, which are very promising for the exploration of electrical spin transfer phenomena. The method allows the electrical connection of one single nanowire in a large assembly of wires embedded in anodic porous alumina supported on Si substrate with diameters and periodicities to be controllable to a large extent. Both magnetic excitations and switching phenomena driven by a spin-polarized current were clearly demonstrated in our electrodeposited NiFe/Cu/ NiFe trilayer nanowires. This novel approach promises to be of strong interest for subsequent fabrication of phase-locked arrays of spin transfer nano-oscillators with increased output power for microwave applications.

Effects of Cu Interdiffusion on the Electromigration Failure of FM/Cu/FM Tri-Layers for Spin Valve Read Sensors

Electromigration-induced failure (EIF) lifetime characteristics of FM/Cu/FM (FM: NiFe or Co) tri-layers, which are currently used in GMR spin-valve read sensors, have been investigated to verify the fundamental failure mechanisms. It is found that the lifetime of NiFe/Cu/NiFe tri-layers was dramatically increased by decreasing the Cu spacer thickness. The obvious shorter lifetime of NiFe/Cu/NiFe tri-layers compared to that of Co/Cu/Co tri-layers was mainly thought to be attributed to the formation of current paths resulted from the electromigration-induced Cu interdiffusion into the top or bottom NiFe layer during electrical stressing caused by the Ni-Cu intermixing. The activation energy (Ea) and current density factor, n value of the NiFe/Cu/NiFe tri-layers were found to be 0.23-0.25eV and 1.23-1.32, respectively. It is suggested that the control of Cu spacer interdiffusion and chemical roughness at the FM/Cu interface is crucial in determining the electrical reliability of FM/Cu/FM based GMR spin valve read sensors

Substantial enhancement in the performance of a spin valve through the ultra-thin insertion of partially oxidized Fe

We found that the ultra-thin insertion of a mix of Fe and Fe oxide in the pinned layer substantially enhanced the performance of a spin valve. With the exchange bias field kept large, the giant magnetoresistance (GMR) reached 11.3%, which corresponded to a 46% increase in GMR compared with the GMR of spin valves without the insertion. We attribute this considerable enhancement to spin-dependent scattering boosted by the combined effect of the modified local electronic structures at the Fe and specular reflections at the α-Fe2O3 of the insertion.

Bare PCB Inspection System With SV-GMR Sensor Eddy-Current Testing Probe

This paper describes bare printed circuit board (PCB) inspection based on eddy-current testing (ECT) technique with high scanning speed. A high-frequency ECT probe composed of a meander coil as an exciting coil and the spin-valve giant magnetoresistance (SV-GMR) sensor was fabricated and is proposed. The ECT probe was designed based on crack inspection over flat surface, especially suitable for microdefect detection on high-density bare PCB. The ECT signal detected by the SV-GMR sensor was acquired by high-speed A/D converter for applying the signal processing based on digital technique. Harmonic analysis based on Fourier transform was used to analyze the ECT signal at fundamental frequency in order to increase inspection speed and this technique allowed the ECT probe to scan bare PCB, with high sampling frequency and with high-spatial resolution inspection. Experimental results verified the possibility and the performance of the proposed PCB inspection system based on ECT technique