Search results for "MAGNETORESISTANCE"
showing 10 items of 173 documents
Spin polarization of magnetoresistive materials by point contact spectroscopy
2003
In the strive to find a straightforward method for determining the spin polarization, the analysis of the Andreev reflection process in point contact junctions has attracted much interest. However, the prerequisite for anevaluation of the transport spin polarization in this scheme is the existence of elastic (ballistic or diffusive) transport, which cannot be assumed a priori. We therefore also include inelastic processes in our analysis and exemplify that thermal effects can have a significant effect on data evaluation. As ferromagnetic samples with a predicted half metallic behavior and comparably low conductivity we used thin films of the double perovskite Sr 2 FeMoO 6 and bulk material …
CVD synthesis of carbon spheres using NiFe-LDHs as catalytic precursors: structural, electrochemical and magnetoresistive properties
2016
The gram-scale synthesis of carbon spheres with a diameter of ca. 740 nm has been achieved by means of a chemical vapour deposition method using NiFe-layered double hydroxides as a solid catalytic precursor. The presence of the catalyst (FeNi3) allows controlling the final size distribution, resulting in a monodisperse sample. Their structural properties exhibited a high degree of graphitization according to their ID/IG ratio. In addition, their morphological features were unveiled by FIB-SEM and HRTEM, showing that they are formed by solid inner cores, and presenting labile chain-like structures due to accretion procedures. The solution and posterior sonication of the samples in toluene ga…
Optical studies of laser-induced gray-tracking in KTP
1999
We have studied gray-tracking induced by a pulsed and polarized 532-nm laser beam in flux grown KTiOPO/sub 4/ (KTP) crystals. Transmission spectra measured under polarized light give different results: gray-tracking leads to an increase in the initial anisotropy of the linear optical properties of KTP, and the polar axis is the most sensitive to this process. The dynamics of relaxation of gray-tracking is anisotropic and depends on the wavelength under analysis. We show a possible induced modification of the crystal surface and also the existence of an intensity above which gray-tracking reaches the saturation point. We then measure the temperature above which gray-tracking no longer exists.
Influence of the covalent grafting of organic radicals to graphene on its magnetoresistance
2013
Graphene was obtained by direct exfoliation of graphite in o-dichlorobenzene (oDCB) or benzylamine, and further functionalized with 4,4′-[(1,3-dioxo-1,3-propanediyl)bis(oxy)]bis[2,2,6,6-tetramethyl-1-piperidinyloxy] (1-TEMPO) organic radicals by using the Bingel–Hirsch cyclopropanation reaction. Here, the use of different solvents permits variation of the density of radicals anchored to the carbon layers. Covalent grafting is unambiguously demonstrated by TGA, μ-Raman, XPS and EPR measurements, which also rule out spurious physisorption. Our transport measurements indicate that the conduction mechanism varies as a function of the density of radicals grafted to the carbon layers. Moreover, t…
Impact of granularity on transport properties of mechanically stressed La0.67Ca0.33MnO3 films
2001
Abstract (La,Ca)MnO 3 is one of so called collosal magnetoresistive materials and it is of interest to correlate its transport properties to film growth in order to optimize its performance. Two-hundred nanometers thick (100)La 0.67 Ca 0.33 MnO 3 films were grown by laser ablation on (100)SrTiO 3 , (100)LaAlO 3 and (100)(LaAlO 3 ) 0.3 +(Sr 2 AlTaO 6 ) 0.7 substrates. The films were granular in structure with low angle boundaries between the grains. The volume of the unit cell was considerably smaller for films grown on a SrTiO 3 substrate than on LaAlO 3 . At temperatures higher than the one where the spins order, the strongest response of resistivity on temperature ρ ( T ) was measured for…
Flexible Magnetoresistive Sensors for Guiding Cardiac Catheters
2018
Cardiac catheterization is a procedure, in which a long thin tube that is called a “catheter” is inserted into the heart for diagnosis or treatment. Due to the excessive use of x-ray doses and contrast agents for orientation detection during the surgery, there is a need to find a better alternative. This paper presents magnetic tunnel junction sensors on flexible Si attached to the catheter tip for orientation detection during minimally invasive surgeries. Due to the small size of catheters, extreme minimization in terms of size, weight, thickness and power consumption is needed for any device implemented on it. The fabricated flexible magnetic tunnel junctions fulfill those requirements wi…
Broadband Terahertz Probes of Anisotropic Magnetoresistance Disentangle Extrinsic and Intrinsic Contributions
2021
Anisotropic magnetoresistance (AMR) is a ubiquitous and versatile probe of magnetic order in contemporary spintronics research. Its origins are usually ascribed to extrinsic effects (i.e. spin-dependent electron scattering), whereas intrinsic (i.e. scattering-independent) contributions are neglected. Here, we measure AMR of polycrystalline thin films of the standard ferromagnets Co, Ni, Ni81Fe19 and Ni50Fe50 over the frequency range from DC to 28 THz. The large bandwidth covers the regimes of both diffusive and ballistic intraband electron transport and, thus, allows us to separate extrinsic and intrinsic AMR components. Analysis of the THz response based on Boltzmann transport theory revea…
Quasi-static magnetoresistive sensor modeling for current-time conversion circuit applications
2011
In this paper we report a current-to-time converter (CTC) suitable for current sensor monitoring in low power applications. Based on a discrete resistence-to-frequency converter and a Giant MagnetoResistance (GMR) current sensor. Simulations have been done using a quasi-static electrical Verilog-A model for the GMR current sensor. A reduced set of parameters has been extracted to characterize the GMR sensor's behavior. The application has been analyzed making use of different sensors, whose device parameters were previously extracted. Finally, the accuracy of the models has been tested by comparing with experimental transient measurements.
Graphene enhances the magnetoresistance of FeNi3nanoparticles in hierarchical FeNi3–graphene nanocomposites
2016
An increase in the giant magnetoresistance of FeNi3 nanoparticles of 20 times has been observed in FeNi3–graphene nanocomposites synthesized using NiFe-layered double hydroxide hybrids as precursors. The magnetic, transport and magneto-transport properties of these nanocomposites are studied and compared with those of the pure FeNi3 nanoparticles. The hierarchical structure and hybrid composition of these magnetic nanocomposites lead to the observation of two unusual magneto-transport properties, namely (i) an enhancement in the low-field magnetoresistance effects, and (ii) a crossover from negative to positive MR upon cooling down the sample.
Temperature and bias-voltage dependence of atomic-layer-deposited HfO2-based magnetic tunnel junctions
2014
Magnetic tunnel junctions with HfO2 tunnel barriers were prepared through a combination of magnetron sputtering and atomic layer deposition. We investigated the tunneling transport behavior, including the tunnel magnetoresistance ratio and the current-voltage characteristics between room temperature and 2 K. Here, we achieved a tunneling magneto resistance ratio of 10.3% at room temperature and 19.3% at 2 K. Furthermore, we studied the bias-voltage and temperature dependencies and compared the results with those of commonly used alumina- and magnesia-based magnetic tunnel junctions. We observed a polycrystalline/amorphous electrode-barrier system via high-resolution transmission electron mi…