Enhancement Of Room Temperature Magnetoresistance Research Articles

Improvement on Electrical Properties and Magnetoresistance Induced by Pd or Ag Addition in La0.67(Ca0.65Ba0.35)0.33MnO3 Manganites

Electrical properties and magnetoresistance have been studied in two series of xAg- La0.67(Ca0.65Ba0.35)0.33MnO3 and xPd-La0.67(Ca0.65Ba0.35)0.33MnC3 (abbreviated by xAg- LCBMO and xPd-LCBMO) composites. Both Pd and Ag addition induce a decrease in resistivity and an increase in temperature at which the resistivity reaches its maximum. This is mainly due to the improvement of grain boundaries caused by the segregation of good conductive metal grains on the grain boundaries/surfaces. In addition, both Pd and Ag addition induce a large enhancement of room temperature magnetoresistance (RTMR). Note that 27% molar ratio of Ag addition induces a large RTMR of about 70%, about ten times larger than pure LCBMO, whereas 27%molar ratio Pd addition brings a much larger RTMR of about 170%. The large enhancements of MR can be attributed to the decrease in resistivity of the samples caused by the good conductive metal. On the other hand, the polarization of Pd atoms near the Mn ions on the grain surfaces/boundaries plays a very important role in the increase in MR, which induces a large number of spin clusters in Pd-added samples.

Large room-temperature magnetoresistance and temperature-dependent magnetoresistance inversion in La 0.67Sr 0.33MnO 3/Alq 3 - Co nanocomposites/Co devices

Large room-temperature (RT) magnetoresistance (MR) and temperature-dependent MR inversion have been observed in tris (8-hydroxyquinoline) aluminum (Alq 3)-cobalt nanocomposites-based organic–inorganic hybrid devices. Negative MR–high resistance for parallel electrodes configuration — due to magnetization reversal of ferromagnetic (FM) electrodes has been observed at low temperatures. As the temperature increases, the MR undergoes a sign change. At room temperature, a positive MR of ∼9.7% with the resistivity dropping monotonously with increasing magnetic fields has been observed. The RT MR is about two orders of magnitude of that in organic-FM nanocomposites measured with nonmagnetic electrodes. The enhancement of RT MR is attributed to the injection of spin polarized carriers into Alq 3-Co nanocomposites.

Giant room temperature electric-field-assisted magnetoresistance inLa0.7Sr0.3MnO3/n-Si nanotip heterojunctions

An on-chip approach for fabricating ferromagnetic/semiconductor–nanotip heterojunctions isdemonstrated. The high-density array of Si nanotips (SiNTs) is employed as a template for depositingLa0.7Sr0.3MnO3 (LSMO) rods with a pulsed-laser deposition method. Compared with the planar LSMO/Si thinfilm, the heterojunction shows a large enhancement of room temperature magnetoresistance (MR) ratio up to 20% under 0.5 T and a bias current of20 µA. TheMR ratio is found to be tunable, which increases with increasing external biasand the aspect ratios of the nanotips. Electric-field-induced metallization, inconjunction with nanotip geometry, is proposed to be the origin for the giantMR ratio.

Electronic transport and extra large magnetoresistance in LCBMO/Pdx composites

Two-phase composites LCBMO/Pdx were synthesized using the sol–gel technique followed by the solid-state reaction. Pd addition induces a remarkable decrease in resistivity, which is mainly related to the improvement of grain boundaries/surfaces caused by the segregation of Pd. The resistivity data for all samples follow the adiabatic small-polaron-hopping model at high temperature above the Curie temperature TC, while in the low temperature region, they are proportional to T2, reflecting that the electron–electron scattering mechanism is dominant in the ferromagnetic metallic state. In addition, Pd addition induces a large enhancement of room temperature magnetoresistance (MR). Especially for the x = 0.27 sample, an extra large magnetoresistance over 170% is obtained at 10 kOe and 289 K. This is the largest MR obtained at room temperature in all kinds of colossal magnetoresistance (CMR) materials. The good conductivity and polarizing effect of Pd are responsible for the enhancement of MR. The former leads to the decrease in resistivity and the latter induces a large number of spin clusters.

Large enhancement of room temperature magnetoresistance in Ag-added La 0.67(Ca 0.65Ba 0.35) 0.33MnO 3

The electrical and magnetoresistant properties of La 0.67(Ca 0.65Ba 0.35) 0.33MnO 3/Ag x (abbreviated by LCBMO/Ag x ) have been studied. The results show that Ag addition causes a decrease of resistivity dramatically and especially induces a large enhancement of room temperature magnetoresistance (MR). The room temperature MR ratio for x=0.27 sample in 10 kOe magnetic field is 41%, almost 20 times larger than that for x=0 sample. This enhancement is related to that the Curie temperature ( T c) of the sample is near room temperature, as well as the significant reduction of resistivity. The good fits of experimental results for x=0.27 sample to Brillouin function indicate that the MR behavior in the Ag added LCBMO is induced by the spin-dependent hopping of the electrons between the spin clusters, which is an intrinsic property of the CMR materials.

Enhancement of room-temperature magnetoresistance in Sr2FeMoO6 by reducing its grain size and adjusting its tunnel-barrier thickness

The intergrain magnetoresistance (IMR) of polycrystalline Sr2FeMoO6 is known to depend on its grain size and the tunnel barrier thickness formed during fabrication. Further enhancement of the IMR of Sr2FeMoO6 is found possible by further decreasing its grain size using high-energy ball milling, as well as by judiciously adjusting the tunnel barrier thickness. The tunnel barrier thickness depends on the amount of insulating nonmagnetic SrMoO4 impurity formed during fabrication, which in turn can be controlled by varying the mixture ratio of the ambient gaseous H2–Ar stream during annealing. With smaller grain size, the magnetic domain size decreases correspondingly and so can be more easily rotated to produce a lower coercive field. The increase in the SrMoO4 impurity phase increases the number of grain boundary barriers in the Sr2FeMoO6 matrix, leading to a larger low-field magnetoresistance effect (LFMR). A significant enhancement of the LFMR was found when the SrMoO4 impurity was close to the conduction threshold. Compared to the artificial fabrication of multilayer structures, our method is much simpler and offers an enhanced technology to fabricate suitable tunneling barriers in magnetoresistive devices.

Enhancement of Room Temperature Magnetoresistance in La<SUB>0.7</SUB>Sr<SUB>0.3</SUB>Mn<SUB>1-x</SUB>Cu<SUB>x</SUB>O<SUB>3</SUB>

A series of perovskite-type compounds La 0.7 Sr 0.3 Mn 1-x Cu x O 3 have been synthesized by solid state reaction with x = 0, 0.03, 0.05, 0.08, 0.10, 0.15, 0.20, 0.25. 0.30. The Curie temperature and transition temperature of metal-insulator decreases when x value increases from 0 to 0.20. There is an enhancement of magnetoresistance ΔR/R 0 of compounds La 0.7 Sr 0.3 Mn 1-x Cu x O 3 at room temperature which may be connected with the shift of Curie temperature and transition temperature of metal-insulator through Cu atom substitution. On the contrary, the increase of resistivity is due to the reduction of the double-exchange interaction.

Enhancement of room temperature magnetoresistance in La 0.67Sr 0.33Mn 1− xTi xO 3 manganites

The enhancement of room temperature magnetoresistance can be induced by the Ti substitution for Mn in La 0.67Sr 0.33Mn 1− x Ti x O 3, which may be connected with the shift of the Curie temperature from a high temperature to the near room temperature by the Ti substitution. This experimental observation may provide a route to improve CMR behavior of the perovskite manganites at room temperature.