Papers by Keyword: Magnetoresistivity MR

Abstract: Magnetic properties of nanocrystalline Ni and Ni-Fe alloys produced by electrodeposition have been studied at 2K and at 298K. Ni and Ni-15%Fe alloy deposits show nano-grain structure with the average grain size of 23 nm and 12 nm, respectively. Both materials exhibit soft magnetic properties. Nanocrystalline Ni at 2K shows saturation magnetization, coercive force, and remanent magnetization of 57 emu/gr, 101 Oe, and 16 emu/gr respectively. Nanocrystalline Ni-15%Fe alloy exhibits superior soft magnetic properties than Ni with corresponding saturation magnetization, coercive force, and remanent magnetization at 2K of 96 emu/gr, 6 Oe, and 4 emu/gr respectively. The magnetic properties and their dependence upon temperature data are interpreted in terms of the Herzer random anisotropy model for nanocrystalline materials.

Abstract: The transport properties of the inhomogeneous system (1/4) Ag₂O-La_0.833Na_0.167MnO₃ (LNMO/Ag) have been systematically studied. X-ray diffraction patterns show that the LNMO/Ag sample is the two-phase composite and consists of a magnetic La_0.833Na_0.167MnO₃ (LNMO) perovskite phase and a nonmagnetic Ag metal phase. The resistivity of the sample decreases dramatically with Ag added into the pure perovskite LNMO manganites. For the LNMO/Ag sample, the Curie temperature T_C is 331 ± 2 K and slightly higher than that of the LNMO sample (323 ± 2 K). Due to the dope of Ag metal, the room temperature magnetoresistance effect is enhanced significantly (from 7% for the pure LNMO manganites to 23% for the LNMO/Ag sample under a relative lower field of 0.5 T and from 37.5% for the LNMO sample to 41 % for the LNMO/Ag sample under a high field of 6 T at the temperature of 330 K. In the low temperature regime, the magnetoresistance ratio of the LNMO/Ag sample is smaller than that of the LNMO sample, which is contrary to the magnetoresistance effect in high temperature. The effects are discussed qualitatively by use of a model which is based on the relative change among the intrinsic magnetoresistance effect and the extrinsic magnetoresistance effect.

Abstract: We observe a large magneto-resistance in very thin Ba₂FeMoO₆ films of ~-12% at 10K, which is not significantly changed when thin NiFe/Ba₂FeMoO₆ bi-layers are made. This suggests that the magneto-resistance in both cases is dominated by inter-grain tunnelling in the Ba₂FeMoO₆ thin film. There is an anomalous peak in the resistance at ~300K in the bi-layer film that can not be easily explained. However, we know that the temperature where this peak occurs is close to the Ba₂FeMoO₆ Curie temperature.

Abstract: We report the results from magnetotransport measurements on polycrystalline Sr_2-xLa_xFeMoO₆ samples at magnetic fields of up to 8 T. We observe a normal as well as an anomalous Hall effect. We find that there is a small decrease in the normal Hall coefficient for La doped samples.

Abstract: We report magnetotransport measurements in single epitaxial graphene layers grown on the C-face of an 8° off-axis 4H-SiC substrate using high temperature annealing conditions with a graphite cap covering the sample. The graphene sheets were found p-type doped, with mobilities varying between 1000 and 11000 cm²/V.s from device to device at 1.6 K. We examine the signature of weak localization and universal conductance fluctuations at weak magnetic field and we show that the phase coherence lengths extracted from the two phenomena are in satisfactory agreement.

Abstract: We investigate the effect of hyperfine interaction on magnetoresistance in nonmagenetic organic semiconductors. A Lorentz-type magnetoresistance is obtained from hyperfine interaction-dependent spin precession picture. The magnetoresistance depends on initial spin orientation of electron to hole in electron-hole pairs. Increasing hyperfine interaction slows down change of the magnetoresistance with magnetic field. The field dependence, the sign and saturation value of the magnetoresistances are composite effects of recombination and dissociation rate constants of singlet and triplet electron-hole pairs.

Abstract: The effects of high energy electron irradiation and high magnetic fields (up to 14 T) on the electrical characteristics of recrystallized p-type polysilicon-on-insulator layers were studied. The aim of the paper is to obtain the material suitable to create the sensors operating in harsh conditions.

Abstract: The paper describes results of investigation on sputtered NiFe Films to determine the sputter deposition condition that could produce magnetic field sensors with the desired magnetic and magnetoresistive properties. The magnetic thin films materials used in such devices should have a low coercive force, a low anisotropy field and low magnetization dispersion, α50 with high magnetoresistance ratio. From the results presented, it is shown that that the most useful films for 82%Ni-Fe composition are produced at 200 °C-250 °C moderate substrate temperatures. It is also possible to specify the substrate bias potential and sputter gas pressure sputter deposition conditions under which the 82%Ni-Fe thin films may be employed for the production of magnetoresistine sensors with near optimum magnetic and magnetoresistive properties. The work also provide understanding of the effects on the magnetic properties of sputtered magnetic films that is very limited as current literature is almost entirely limited to evaporated magnetic films.

Abstract: The electrical–magnetic transport properties of (La0.7Ca0.3MnO3)(1-x)/(BN)x composites has been investigated systemically by conventional solid-state reaction method. The results of X-ray diffraction (XRD) and scanning electronic microscopy (SEM) show that BN and LCMO coexist in the composites and BN mainly goes into the grain boundary region without any chemical reaction with La0.7Ca0.3MnO3, which are in accordance with the results of the magnetic measurements. It is very interesting that with increasing of BN content level (x < 0.25), the metal–insulator transition temperature (TP) remains constant (nearly at 275K), and the resistivity increases very slowly. But when x > 0.25, TP shifts to lower temperature and the resistivity increases dramatically. The resistivity threshold of the composites occurred at x = 0.25, and specially the magnetoresistance (MR) reaches a maximum value (about 26.32 %) at 100K in an applied magnetic field of 3kOe. The results also indicate that the doped BN has an important effect on the low field MR (LFMR), which results from spin-polarized tunneling.

Abstract: The electrical and optical techniques have been applied for investigation of carrier transport and recombination features in thick free-standing 3C-SiC layers. Temperature dependencies of Hall mobility, magneto-resistivity, and conductivity indicated presence of high potential barriers, up to 0.4 eV. The carrier mobilities and equilibrium densities were calculated in the barrier and inter-barrier regions. Contactless measurements of the excess carrier ambipolar mobility and lifetime at 1016-18 cm-3 injection levels revealed carrier scattering solely by phonons in 80 – 800 K range. A correlation between the temperature dependencies of carrier lifetime and ambipolar mobility pointed out that diffusion-limited surface recombination at extended defects contributes significantly to the carrier lifetime.