Papers by Keyword: Magnetoresistance

Abstract: The manganite systems investigated during the present work are pure La_0.85Te_0.15MnO₃ (LTMO) and its composite with 12% concentration of Al₂O₃ nano powder (LTMO + Al₂O₃). The materials were prepared by the modified auto combustion technique. The samples were characterized by X-ray diffraction. The powder X-ray diffraction pattern of pure LTMO at room temperature shows that sample is in single phase with no detectable secondary phases and the sample have a rhombohedral structure in hexagonal with the space group R3c. The XRD pattern of LTMO + 12% Al₂O₃ indicates the clear presence of Al₂O₃ nano phase in the composite. In the present study, the FTIR Spectroscopy of both samples was carried out. It is clear from the Vibrational assignment for the value of corresponding peak position of FTIR spectra that no extra unwanted impurity is present in samples. A quantitative analysis of the energy dispersive spectroscopy (EDS) data indicates that the observed concentration of elements are very close to the calculated values from its chemical formula. R-T measurements reveals that the addition of secondary phase in manganite strongly influenced on electronic and magnetoresistance behaviour. We summarise some of the salient features of the results.

Abstract: As a new type of unsaturated linear magnetoresistive materials, tungsten ditelluride series material has potential applications in the fields of strong magnetic detection, information recording and magnetic storage devices. The current development concepts of “green materials”, “green chemical technology” and “environmentally friendly technology” require us to pursue the non-toxic, low-emission and non-emission in material synthesis technology. At the same time, the prepared products show excellent performance and high versatility and efficiency. According to our previous work, the study attempts to use a low-volatile amine solvent as a pretreatment raw material to synthesize a tungsten germanium-based linear magnetoresistive material by hydrothermal/solvothermal method and self-fluxing method. The obtained materials were subjected to XRD, Raman, SEM and Magnetoresistance. Experimental results show that when the mass ratio of W and Te is 1:4, the prepared material is pure phase and the sample is the layered structure. The Magnetoresistance Property points out that the maximum value is about 190 %, which appears in the condition of 10 K and 7 T. Those test projects include phase, structure and morphology characteristics, and provide technical parameters and methods for the development of green synthesis and potential applications of tungsten ditelluride series linear magnetoresistive materials.

Abstract: Mixed valence manganite materials have been studied due to their interesting physical properties such as their magnetoresistance (MR) effect. The change of Mn³⁺/Mn⁴⁺ ratio affects the possible bonds between anion and cation and their spin structure that may occur in the samples. The aim of this research is to study the change of magnetoresistance effect and magnetic properties of La_0.67Sr_0.33MnO₃ (LSMO) by doping the Mn site with Ni ion. La_0.67Sr_0.33Mn_1-xNi_xO₃ samples were synthesized by using sol-gel method and characterized by using X-ray diffractometer (XRD) and Energy Dispersive X-ray spectroscopy (EDX) to confirm whether Ni has been doped successfully to the parental compound or not. XRD results showed that the samples have a single phase and Ni peak has been detected in the EDX result of Ni-doped LSMO. Resistivity and magnetic measurement showed that LSMO material has ferromagnetic metallic behavior, while x = 0.20 Ni-doped LSMO sample showed paramagnetic insulator behavior. The absolute value of the MR for un-doped sample is higher than the doped sample when the low field is applied, while under the influence of the high magnetic field, it become smaller than the doped sample.

Abstract: This paper studies the aspect ratio (W/L), width (W) per length (L) of semiconductor resistor based on Hall effect current mode for horizontal magnetic field. At low concentration, 10¹⁴ cm^-3, W/L < 1, the length has direct effect to magnetoresistance. The W/L = 1, the large resistor provides magnetioresistance better than small device. The W/L ˃ 1, the width has inversely proportional to magnetoresistance. The %MR(B) is around 1 % at 0.5 T, 1 mA. The long resistor (W/L < 1) can create ΔR in the order of several kilo ohms and several hundred ohms for short resistor (W/L > 1). The contribution factors ρ (L/W) for high ΔR are low concentration and aspect ratio (W/L < 1). The high %MR(B) is contributed by high current density of short structure (W/L > 1). At high concentration 10¹⁷ cm^-3, aspect ratio and magnetoresistance are not sensitive to magnetic field because the Hall effect hardly occurs in high concentration material.

Abstract: In this work the results of substrate temperature effects on coercivity and magnetoresistance in ferromagnetic structures are shown. It was found that with an increase of the substrate temperature from 270 to 390 °C the magnetoresistance increases from 1.2 to 2.3% and the coercive force from 1.6 to 5.3 Oe. A new topology of anisotropic magnetoresistive structures is proposed. In these structures the shape of ferromagnetic elements repeats the shape of nonmagnetic conducting shunts. Sensitivity values obtained for both types of magnetic structures are compared.

Abstract: We explore the magnetic sensing capabilities of two 4H-SiC n⁺p diodes fabricated by NASA Glenn which only differ in the implanted ion species, nitrogen and phosphorus, and the implant activation annealing time. We use low-and high-field electrically detected magnetic resonance (EDMR) to investigate the defect structure used to sense magnetic fields as well as to evaluate the sensitivity. In addition, we expose these devices to high energy electron radiation to evaluate the defect sensing capability in a harsh radiation environment. The results from this work will allow us to tailor our processing methods to design a more optimal 4H-SiC pn diode for magnetic field sensing in harsh environments.

Abstract: A series of polycrystalline bulk samples (Pr_0.67Sr_0.33MnO₃)_1-x/ (NiO)_x were prepared by solid state reaction, and its structure, electrical transport and magnetoresistance properties were investigated. X-ray analysis showed that parent compound of Pr_0.67Sr_0.33MnO₃ (PSMO) formed in single phase with crystal structure of orthorhombic while secondary phase of NiO can be detected with the addition of composite. The electrical properties showed that the resistivity increased with the addition of NiO due to enhancement of spin dependent-tunneling scattering across the artificial grain boundaries of NiO layer. Magnetic field dependence MR curve at various temperatures clearly indicates that extrinsic magnetoresistance had been enhanced due to addition of NiO as the artificial grain boundary.

Abstract: We report the electrical-transport and magnetic properties of the hole doped La_0.7Ca_0.3MnO₃ (LCMO-1) and La_0.88Ca_0.12MnO₃ (LCMO-2) single crystals, prepared using floating zone technique. The metal to insulator transition (T_MI) occurs at 211 K along c-axis and T_MI = 185 K along ab-plane for LCMO-1 single crystal. No electronic transition was observed over the whole temperature range under the magnetic field up to 8 T for LCMO-2 single crystal. It is observed that the T_MI is higher along c-axis as compared to that in the ab-plane, consequently signifying more favorable hoping of electrons is along c-axis in LCMO-1. The ac-susceptibility measurement shows that ferromagnetic to paramagnetic transition temperature (T_C) at 206 K for LCMO-1 and T_C = 118 K for LCMO-2 single crystals which is seemingly related to notable change of resistance at 120 K in LCMO-2 single crystal. The maximum MR of 98% for LCMO-1 and 59% for LCMO-2 single crystals up to 8 T applied magnetic field along c-axis and ab-plane, respectively are observed.

Abstract: We report the electrical-transport, magneto-transport, and magnetic properties of the hole doped La_0.7Ca_0.3MnO₃ (LCMO) and La_0.7Ca_0.24Sr_0.06MnO₃ (LCSMO) single crystals, prepared using floating zone technique. The resistivity data shows the metal to insulator transition (T_MI) occurs at 211 K and 290 K for LCMO and LCSMO single crystals respectively. The electrical transport mechanisms of these crystals are investigated by using different theoretical models, for temperatures below and above T_MI. The magnetization measurements show that these single crystals exhibit ferromagnetic to paramagnetic transition temperature (T_C) at 208 K for LCMO and 273 K for LCSMO single crystals. From device application point of view, both samples show the maximum MR of 98% for LCMO and 80% for LCSMO at 8 T applied magnetic field, while for bolometer IR detectors application point of view the temperature coefficient of resistance (TCR) are found to ~17% K^-1 and 28% K^-1 for LCMO and LCSMO respectively.

Abstract: Silicon carbide (SiC) is well known by the semiconductor industry to have significant potential for electronics used in high temperature environments due to its wide bandgap. It is not so well-known, however, that SiC also has great potential in the area of magnetic field sensing. Using the recently demonstrated zero-field spin dependent recombination (SDR) phenomenon that naturally arises in SiC based devices, near-zero magnetic field measurements can be made with moderately high sensitivity.