Papers by Keyword: Giant Magnetoresistance

Abstract: The giant magnetoresistance (GMR) thin film with spin valve (SV) structure of Ta (2 nm)/Ir₂₀Mn₈₀(10 nm)/Co₉₀Fe₁₀(3 nm)/Cu (2.2 nm)/Co₈₄Fe₁₀B₄(10 nm)/Ta (5 nm)] fabricated by RF magnetron sputtering method with a magnetoresistance (MR) of 6% was used in this work. Green synthesis of Fe₃O₄ magnetic nanoparticles (MNPs) using Moringa Oleifera (MO) leaf extract have been successfully conducted using the coprecipitation method. Fe₃O₄ MNPs demonstrated the inverse cubic spinel structure with the average crystallite size of 13.8 nm and decreased to 11.8 nm for Fe₃O₄/PEG. Fe₃O₄, as a magnetic label, integrated with a Wheatstone bridge-GMR sensor provides access to GMR-based biosensors. The induced-field increase leads the signal (ΔV) to increase with increasing nanoparticle concentration. It was discovered that a sensor can distinguish different types of magnetic labels. The sensitivity for Fe₃O₄ and MO-green synthesized Fe₃O₄ magnetic label was 0.04 and 0.1 mV/g/L, respectively. The GMR sensor performed the highest sensitivity on the MO-green synthesized Fe₃O₄ label. Thus, the SV thin film as a sensor and the green-synthesized Fe₃O₄ nanoparticles as a superior magnetic label are an excellent combination for biosensor application.

Abstract: Structural features of interfaces in [Co/Cu]_n superlattices obtained by magnetron sputtering have been studied by nuclear magnetic resonance (NMR). Modification of interface structural characteristics and magnetoresistive properties of the superlattices with the increase of the number of [Co/C] bilayers is analyzed. Correlation between magnetoresistance and interface structural characteristics has been revealed.

Abstract: Fe/In₂O₃ magnetic granular films have been prepared by radio frequency sputtering (rf) method. The results reveal that the nanometer-sized Fe grains uniformly disperse in the amorphous matrix In₂O₃ for the as-deposited samples. At room temperature, the Fe_0.35/(In₂O₃)_0.65 film shows a superparamagnetic behavior and 5.2% magnetoresistance (MR) ratio is obtained. The susceptibility measurements manifested that the blocking temperature is 50 K. Blow a certain freezing temperature Tf about 10K, the film transits from ferromagnetic state to a composite-cluster state in which the Fe atoms dispersed randomly in In₂O₃ severs as intermedia to couple the Fe grains together. In this case, the MR ratio of the film increases dramatically and a maximum giant magnetoresistance (GMR ) ratio up to 82.4% is obtained at 2.2 K, which is quite different to the MR effect at room temperature. The mechanism of this GMR is attributed to the increase of the hopping mobility of carriers under the applied magnetic field.

Abstract: 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.

Abstract: The physical properties of nano-Mn3O4 is Characterize by theory base clusters of Physical Chemistry, Including the lattice structure, catalytic properties, the phenomenon of giant magnetic and giant magnetoresistance, N dimensional wave function is approximation to be expressed as variational parameters of nonlinear multivariate function by Density Functional Theory, Extreme functional is obtained by Wavelet analysis ,And analyzed the data characteristics on relationship between Particle size, concentration, temperature, magnetic field strength of a4 , a5 and time, Compared with bulk materials, nano materials, bond angles, bond length parameters, Resolved electron spin states and relativistic effects of the problem, Correction of the uneven distribution of electron density because the error caused.

Abstract: The effect of Cr-buffer-layer thickness on the structure, giant magnetoresistance, and coercivity of DC sputtered Cr(tCr)/[Co90Fe10(15Å)/Cu(23Å)]8/Cr(10Å) superlattices has been investigated. A drastic change of hysteresis in a short interval of the buffer layer thickness (15 ÷ 20 Å) has been revealed. It has been shown that in superlattices with low coercivity the (111) texture is present, whereas superlattices without texture demonstrate a large coercivity and high GMR ratio.

Abstract: We analyze the effect of the geometrical shape and size of the cross section on the spin-polarized transport and the giant magnetoresistance (GMR) by a finite element method, and evaluate the stability and the physical properties of nano-scale spin valves. We calculate the transmission coefficients in the ballistic regime by using a transfer-matrix method, and evaluate the GMR of the current perpendicular to the plane (CPP) by using a circuit theory. The conduction-band structure is simplified to the potential step, which is determined by combining the interfacial parameters calculated by first-principles with the free electron model. The geometrical shapes of the cross section are line and square. As a result, the cross sectional shape has a significant effect on the spin-polarized transport and the GMR. The square-shaped cross section has an advantage of the large GMR, which is contrary to the line-shaped cross section. These phenomena result from the difference of the cut-off energies with the transverse modes and, consequently, the different spin-down transmission coefficients.

Abstract: The potential barrier at the metal/oxide junction in a specular spin valve structure with nano-oxide layers has been mapped by off-axis electron holography in a field emission gun transmission electron microscope. A potential jump of ~3V across the metal/oxide junction was detected. Presence of the potential barrier confirms formation of metal/insulator/metal structure, which contributes to confinement of conductance electrons with spin polarity characteristic in the key SV structure by the specular reflection of the spin-polarized electrons at the metal/oxide junction and leads to nearly double enhancement of magnetoresistance (MR) ratio from 8% to ~16%.

Abstract: A series of (Fe50Ni50)xCu1-x granular films were prepared using magnetron controlled sputtering method. The magnetic-transport and microstructure of FeNi-Cu films deposited at room temperature and then annealed at various temperatures were investigated through TEM, XRD and conventional four probes method under room temperature, respectively. The giant magnetoresistence (GMR) as a function of FeNi volume fraction for as-deposited FeNi-Cu films reached a maximum of about 1.8 % at the volume fraction of 32 %. With increasing the annealing temperature, the GMR of films with the volume fraction less than 26 % reaches a peak at certain annealing temperature. While for films with the volume fraction larger than 26 %, the GMR have almost no changes at first and then decrease with increasing the annealing temperature. In addition, the relationship between magneto-transport and the microstructure, morphology of granular films is discussed.

Abstract: Half metallic ferromagnets are candidate materials for novel electronic devices, which can control the spin character of the conducting electrons. Electronic band calculation predicted that Co2MnGe Heusler compounds may has the half metallic band structure. In the present study, structure and magnetic properties have been investigated of the Co2MnGe for bulk and thin films. In the bulk sample, plate defects have been found.