Application of magnetically modulated microwave absorption to study of giant magnetoresistance effect in the Ni−Fe/Cu multilayer system

Magnetically modulated microwave absorption (MMMA), magnetic hysteresisM(H), giant magnetoresistance (GMR) and ferromagnetic resonance (FMR) have been examined in the antiferro-magnetically coupled Py/Cu (Py=Ni₈₃Fe₁₇, permalloy) multilayer system. The correlation between results obtained by the MMMA technique, the standard GMR measurements, and magnetization reversal studies is shown. Microwave studies of GMR, magnetization reversal, and FMR for different orientations of the magnetic field with respect to the sample surface are presented.     

Electrodeposition and characterization of Cu/Co multilayers: Effect of individual Co and Cu layers on GMR magnitude and behavior

The present work discusses the successful electrodeposition of Cu/Co multilayers, exhibiting appreciable GMR of 12-14% at room temperature. The effect of individual Cu and Co layers on the magnitude and behavior of GMR has been studied. By varying the thickness of individual layers the field at which saturation in GMR is observed can be controlled. It was observed that for lower thicknesses of Co layer, the saturation fields are reduced below 1 kOe. The Cu layer thickness seems to control the nature of magnetic coupling and the saturation field, with the two showing a correlation.     

High efficiency giant magnetoresistive device based on two-dimensional MXene (Mn2NO2)

Due to the unique electronic structure of half-metals, characterized by the conductivity of majority-spin and the band gap of minority-spin, these materials have emerged as suitable alternatives for the design of efficient giant magnetoresistive (GMR) devices. Based on the first-principles calculations, an excellent GMR device has been designed by using two-dimensional (2D) half-metal Mn₂NO₂. The results show that Mn₂NO₂ has sandwiched between the Au/nMn₂NO₂ (n = 1, 2, 3)/Au heterojunction and maintains its half-metallic properties. Due to the half-metallic characteristics of Mn₂NO₂, the total current of the monolayer device can reach up to 1500 nA in the ferromagnetic state. At low voltage, the maximum GMR is observed to be 1.15 × 10³¹ %. Further, by increasing the number of layers, the ultra-high GMR at low voltage is still maintained. The developed device is a spintronic device exhibiting the highest magnetoresistive ratio reported theoretically so far. Simultaneously, a significant negative differential resistance (NDR) effect is also observed in the heterojunction. Owing to its excellent half-metallic properties and 2D structure, Mn₂NO₂ is an ideal energy-saving GMR material.     

Interfacial roughness and angle dependence of giant magnetoresistance in magnetic superlattices

Using the two-point conductivity formula, we numerically evaluate the giant magnetoresistance (GMR) in magnetic superlattices with currents in the plane of the layers (CIP), from which the effect of the interfacial roughness and magnetization configuration on the GMR is studied. With increasing interfacial roughness, the maximal GMR ratio is found to first increase and then decrease, exhibiting a peak at an optimum strength of interfacial roughness. For systems composed of relatively thick layers, the GMR is approximately proportional to ,where is the angle between the magnetizations in two successive ferromagnetic layers, but noticeable departures from this dependence are found when the layers become sufficiently thin. Received 21 September 1998 and Received in final form 22 December 1998     

Giant magnetoresistance (GMR) and ferromagnetic properties of DC and pulse electrodeposited Cu–Co alloys

Cu–Co ferromagnetic alloys occurring as granular films and exhibiting giant magnetoresistance (GMR) property have been synthesized using both DC and pulse electrodeposition techniques. The growth process of these electrodeposits comprising multiple granules of disparate morphology, magnetic features exhibits critical dependence on electrodeposition conditions. Using ferromagnetic resonance and magnetic hysteresis data, we have attempted a correlation between evolution of these electrodeposits and their ferromagnetic properties with special emphasis on GMR property.     

Quantum Theory for Interfacial Roughness and Angle Dependence of Giant Magnetoresistance in Magnetic Multilayers

The giant magnetoresistance(GMR)in magnetic multilayers with current in the plane of the layers is studied by using the quantum-statistical Green‘s function approach,in which the effects of the interfacial roughness and magnetization configuration on the GMR are included,It is shown that the maximal GMR first increses and then decreases with increasing interfacial roughness,exhibiting a peak at an optimum value of interfacial roughness.An approximately linear dependence of GMR on sin^2(θ/2)is obtained,where θ is the angle between magnetizations of the two successive ferromagnetic layers,FUrthermore,the maximal GMR is found to increase with increasing the number of bilayers.     

Degradation of the Giant Magnetoresistance in Fe/Cr Multilayers Due to Ar-Ion Beam Mixing

The influence of 200 keV Ar-ion irradiation on the interlayer coupling in the Fe/Cr multilayer system exhibiting the giant magnetoresistance effect (GMR) is studied by conversion electron Mössbauer spectroscopy (CEMS), VSM hysteresis loops, magnetoresistivity and electric resistivity measurements and supplemented by the small-angle X-ray diffraction (SAXRD). The increase of Ar ion dose causes an increase of interface roughness, as evidenced by the increase of the Fe step-sites detected by CEMS as a result of which the GMR gradually decreases and vanishes at doses exceeding 1×10¹⁴ Ar/cm². A degradation of GMR with increasing Ar-ion dose is related to the formation of pinholes between Fe layers and the decrease of the antiferromagnetically coupled fraction.

     

Microcharacterization of the surface oxidation of Py/Cu multilayers by scanning X-ray absorption spectromicroscopy

The local surface oxidation of the permalloy surface layer in Py/Cu GMR multilayers on a micron lateral scale has been analyzed by means of a microspot-X-ray absorption spectromicroscope utilizing synchrotron radiation from the Advanced Light Source bending magnet beamline 6.3.2. Additionally, the GMR multilayer samples prepared by dc magnetron sputtering have been analyzed by cross-sectional transmission electron microscopy, hard X-ray reflection and magnetoresistance measurements. The formation of a passivating iron-oxide layer on the sample surface was identified by X-ray absorption near edge structure spectroscopy (XANES) near the Fe-2p edge while no indication for nickel-oxide formation could be found. Small micron-size pits of reduced iron-oxide concentration could be identified by XANES microscopy while the corresponding nickel distribution appeared to be homogeneous. The results are explained in terms of a local breakdown of the passivating oxide layer. Received:16 October 2000 / Accepted: 4 December 2000 / Published online: 21 March 2001     

Enhanced granular magnetoresistance due to ferromagnetic layers

Giant magnetoresistance (GMR) of sequentially evaporated Fe-Ag structures has been investigated. Direct experimental evidence is given, showing that inserting ferromagnetic layers into a granular structure significantly enhances the magnetoresistance. The increase in the GMR effect is attributed to spin polarization effects. The large enhancement (up to more than a fourfold value) and the linear variation of the GMR in low magnetic fields are explained by scattering of the spin polarized conduction electrons on paramagnetic grains.     

Spin valves with CoO as an exchange bias layer

The temperature dependence (50–300 K) of the magnetoresistance and exchange bias field of spin valves with a CoO exchange bias layer have been investigated. At room temperature the GMR effect is enhanced in comparison with spin valves with a FeMn biasing layer. This enhancement increases for decreasing temperature for small Cu thicknesses. No influence of the antiferromagnetism of CoO on the GMR has been observed upon crossing of the Néel temperature.     

Improved giant magnetoresistance in magnetic granular Co5 Cu95 alloys by direct-current joule heating

The dc joule heating technique has been used to produce giant magnetoresistance (GMR) Co₅Cu₉₅ granular alloys. At T=10 K, GMR as large as 28.5% has been observed in the as-quenched sample annealed with I=6A in a magnetic field up to 30 kOe. At room temperature, the joule-heated samples show higher GMR in comparison with that annealed by the conventional method.     

Improved giant magnetoresistance in magnetic granular Co5 Cu95 alloys by direct-current joule heating

The dc joule heating technique has been used to produce giant magnetoresistance (GMR) Co₅Cu₉₅ granular alloys. At T=10 K, GMR as large as 28.5% has been observed in the as-quenched sample annealed with I=6A in a magnetic field up to 30 kOe. At room temperature, the joule-heated samples show higher GMR in comparison with that annealed by the conventional method.     

Optimizing the quality factor of a wideband guided-mode resonance biosensor

This work studies the effect of the biochemical molecular layer on the quality factor of guided-mode resonance (GMR) filter of an ultrasensitive label-free biosensor. A GMR biosensor with a narrower bandwidth has a higher sensitivity but requires much higher accuracy in its fabrication process. In this study, we have managed to present a GMR filter with a narrow bandwidth that requires less precision by controlling the thickness of the biochemical molecule layer, which increases the Q factor by up to three times.     

Theoretical Analysis of the Biological Thermal Effect of Millimeter Waves in Layered-Dielectric-Slabs

The theory is presented for one method of determining the biological thermal effect of millimeter waves in microwave radiometry. It has been studied theoretically that millimeter waves propagation and absorption in a human body. The model is a plane straticulate homogeneous slab of tissues under the irradiance of normal incidence plane wave. It has been discussed by obtaining the electromagnetic field, absorbent power, specific absorption rate, temperature field and their distributions in the human trunk model. Also, the principle of thermal therapeutics of millimeter waves to cancer has been discussed preliminarily.     

非线性响应对自旋阀磁电阻的影响

从非线性Kubo公式出发,考虑电子自旋相关体散射, 研究了自旋阀结构磁电阻效应.发现非线性响应在不同程度上影响巨磁阻效应.在零温附近,温度参数对磁电阻影响较小,而外加偏压对磁电阻的影响相对较大.     

High sensitivity GMR with small hysteresis in Ni–Fe/Cu multilayers

Giant magnetoresistance (GMR) effect and magnetisation reversal processes have been investigated in Py/Cu(Py=Ni₈₃Fe₁₇,permalloy) multilayers (Mls) obtained by face-to-face sputtering method. The investigated films had constant sublayer thicknesses both for Py and Cu (d_Cu=2nm,d_Py=2nm) and various numbers of ferromagnetic sublayers. It has been shown that for such Mls a high field sensitivity of GMR effect (S≈0.4%/Oe) and negligible hysteresis can be obtained for a low number of Py layers.     

Absorption transition of He-Ne laser in Plasma generated by microwave

Plasma luminescence has been measured in the visible range from 200 to 800 nm. The effect of collisions with sputtered copper ionic species at different argon gas pressures on the emission light intensity has been studied. The behaviour of well resolved lines at 210 and 657 nm as a function of gas pressure and microwave radiation power is measured. The transmission of He-Ne laser line (632.8 nm) through the induced plasma shows dependence on the microwave radiation power. There are observed transitions for the absorption of laser intensity for the filling gas pressures 0 and 5.3 torr at the radiation power of 175 W.     

Microwave absorption studies of MgB2 superconductor

Microwave absorption studies have been carried out on MgB₂ superconductor using a standard X-band EPR spectrometer. The modulated low-field microwave absorption signals recorded for polycrystalline (grain size ∼ 10 μm) samples suggested the absence of weak-link character. The field dependent direct microwave absorption has been found to obey a ✓H dependence with two different slopes, which indicated a transition from strongly pinned lattice to flux flow regime.     

Effect of the structural quality of the buffer on the magnetoresistance and the exchange coupling in sputtered Co/Cu sandwiches

The effect of the structural quality of the buffer stack on the structural properties, giant magnetoresistance (GMR) and the quality of the antiferromagnetic coupling has been investigated for Co/Cu/Co sandwiches prepared by DC-magnetron sputtering. Three kinds of buffers were employed: type A: Cr(6 nm)/Co(0.8 nm)/Cu(10 nm), type B: Fe(6 nm)/Co(0.8 nm)/Cu(10 nm) and type C: Cr(4 nm)/Fe(3 nm)/Co(0.8 nm)/Cu(10 nm). For B and C type buffers, the antiferromagnetic alignment is very interesting at zero field with a coupling strength larger than 0.4 erg/cm² and a GMR signal reaching 5% at room temperature. However, for the A type buffer the antiferromagnetic coupling completely disappears, while the GMR drops to about 0.8%. X-ray diffraction, atomic force microscopy and transmission electron microscopy have been performed in order to understand the origin of the observed difference in the magnetic properties. The results show a strong difference in the average surface roughness, 1.15 nm and 0.35 nm, respectively for the A and C types buffers, and demonstrate that the quality of the surface of the buffer is the key to optimize both the GMR and the indirect exchange coupling. Received 11 July 2000     

Performance of conformal guided mode resonance filters

Guided mode resonance (GMR) filters are highly functional micro-optics capable of narrowband spectral filtering. GMR devices have previously been demonstrated on flat substrates using a wide range of materials and configurations. In this Letter, we apply a soft lithographic technique followed by the deposition of dielectric layers to generate GMR filters on a concave lens surface. Resonances of the resulting conformal GMR filters are experimentally measured and characterized, and the results are compared to the performance of similar GMR filters fabricated on flat surfaces.