Papers by Keyword: CMR

Abstract: Colossal magnetoresistive (CMR) materials have huge potential in modern application and it has been widely used in magnetic sensing industry. From the literature, an incorporation of secondary insulating phase into mixed-valence manganites could improve its extrinsic effect especially low-field magnetoresistance (LFMR). However, nanoparticle addition could lead to substitution and diffusion with its parent compound. In this work, the structural and electrical properties of La_0.7Ca_0.3MnO₃ (LCMO) were investigated by adding the α-Fe₂O₃ nanoparticle with ratio of 0.00, 0.05, 0.10, 0.15 and 0.20 as the artificial grain boundaries. The LCMO compound has been synthesised using sol-gel route. The samples were chosen to sinter at 800°C to obtain the pure LCMO phase by referring to the thermogravimetric analysis (TGA). The structural properties were investigated by an X-ray diffractometer (XRD) while electrical properties were measured by a four-point probe (4PP) system. XRD patterns showed the coexistence of two phases (LCMO & α-Fe₂O₃). LCMO crystallised in orthorhombic structure with space group Pnma while α-Fe₂O₃ exhibited in hexagonal form with space group R-3c. As the content of α-Fe₂O₃ increases, the resistivity of the samples increases drastically. Nevertheless, the addition of iron oxide has no significant effect on the metal-insulator transition temperature (T­_MI). From the XRD and 4PP analysis, it can be deduced that the α-Fe₂O₃ nanoparticles do not react with LCMO compound and successfully formed the La_0.7Ca_0.3MnO₃ /α-Fe₂O₃ composites. The resistivity increases when the nano-sized α-Fe₂O₃ is added into LCMO nanocomposites due to the insulator nature of α-Fe₂O₃.

Abstract: A systematic investigation of neodymium-based manganite, Nd_0.7Sr_0.3MnO₃, was undertaken with a view to understand the influence of sintering temperature on various physical properties. The materials were prepared by the a soft chemical approach of co-precipitation method by sintering at four different temperatures starting from 700 to 1000 °C, with an interval of 100 °C. X-ray diffraction (XRD), transmission electron microscopy (TEM) and D. C. four-probe resistivity were employed to study the crystal structure, average particle size and electrical property respectively. Analysis of XRD patterns shows that all the samples exhibit single phase orthorhombic crystal structure. We followed William-son Hall approach to calculate the lattice stain (ε).These materials were found to exhibit different metal-insulator transition temperature (T_MI) for the different sintering temperature. The value of T_MI increases, as the sintering temperature increases, whereas ε decreases. TEM results show that with the increment of sintering temperature, the particle size of the NSMO samples also increases, which plays a key role on electrical transport. To understand the conduction mechanism in metallic and insulating regions of resistivity, various theoretical models are discussed in this communication.

Abstract: The composites of (1-x)La0.7Ca0.3MnO3/xCoO and (1-x)La0.7Sr0.3MnO3/xCoO (x =0 ~ 0.09) were fabricated by conventional solid state reaction method, and their electrical transport and magnetoresistance (MR%) properties were investigated by physical property measurement system (PPMS). The result of x-ray diffraction (XRD) and scanning electronic microscopy (SEM) indicated that no new phase appeared in the composites except manganites matrix and CoO phases. CoO is mainly distributed at the grain boundaries and surfaces of the matrix. The resistivity LCMO and LSMO based composites were measured in the range 90-320K and 90-400K, respectively. The applied magnetic field is 0T and 0.5T. The observed variation of MR with varying Ca and Sr concentration has been qualitatively investigated.

Abstract: The magnetotransport behaviors of electron-doped colossal magnetoresistance (CMR) manganites La0.9Te0.1MnO3 have been investigated in external magnetic fields up to 4 T. The temperature dependence of the resistivity shows that the transport mechanisms of the sample below the metal-insulator transition temperature are attributed to the electron-phonon and magnon scattering behaviors. While the resistivity above Curie temperature (Tc=240 K) can be fitted with either polaron transport or variable-range hopping, and the fitting results are affected significantly by the magnetic fields. The electron spin resonance investigation indicated that there exist the ferromagnetic clusters up to 280 K in the paramagnetic phase of the sample. As a result, a possible correlation between the resistivty and phase separation is considered.