Charge Transport and Colossal Magnetoresistance Phenomenon in La1−xZrxMnO3

In this study we have investigated the magnetic and electrical transport properties of Zr doped lanthanum manganite perovskite. The structural, magnetic, and transport properties of the Zr doped compounds were determined using x-ray diffraction, dc magnetic susceptibility, and a four probe method for electrical resistivity and magnetoresistance measurements in the temperature range of 5–400 K. The structure of the compounds was found to be rhombohedral. The magnetization versus temperature curves show ferromagnetic regions with the magnetic transition temperatures getting saturated for x ≥ 0.07 compounds. The resistivity curves show decreasing resistivity with increasing Zr content in the compound. The resistivity of the compounds is very high and is explained as due to the localization tendency of the electrons. The metal–insulator transition temperature shows a compositional dependence and has additional contributions apart from magnetism. The results are explained by the double exchange interaction and Mn2+/Mn3+ ratio, and also by taking into account the competition between the core-spin interaction and double exchange interaction

Risk, Ambiguity - Gains, Losses

We use a multiple price list (MPL) method to elicit attitudes to risky and ambiguous prospects. In particular we wish to investigate if there are differences in agent behaviour under uncertainty over gain amounts vis a vis uncertainty over loss amounts. On an aggregate level, we find that (i) in the domain of risk, subjects are risk averse over both gain and loss lotteries with the degree of risk aversion being lower for losses than gains, (ii) subjects are ambiguity averse over ambiguous prospects that involve gains, but that they are mildly ambiguity seeking over such prospects that involve loss and (iii) attitudes toward risk and ambiguity are positively correlated in the domain of gains and are independent of each other in the domain of losses. These behavioural observations are statically significant using both parametric as well as non-parametric tests. Further analysis shows that at an individual level, (a) in the domain of risk, there is a high incidence of a reflection effect across gains and losses though the subjects’ behaviour is bimodal, that is, many are risk averse in gains and risk seeking in losses while many others are risk seeking in gains and risk averse in losses, while (b) in the domain of ambiguity, there is also a high incidence of a reflection effect although almost all such cases exhibit ambiguity aversion in gains and ambiguity seeking in losses.

Magnetic and Electronic Transport Properties of YbxCa1−xMnO3 Compounds

The polycrystalline YbxCa1−xMnO3 (x=0.1,0.2) were studied by x-ray powder diffraction, magnetic, and electrical resistivity measurements. The YbxCa1−xMnO3 crystallizes in an orthogonally distorted perovskite structure, and shows the ferromagnetic ordering with TC more than 110 K. However, the field dependence of magnetization and electrical resistivity exhibits very complicated behavior. A magnetic field induced insulator–metal transition has been found in the Yb0.2Ca0.8MnO3 compound. In addition, the large asymmetry in magnetization and resistivity hysteresis loops has been observed in this compound at 10 K, which might be due to the charge ordering and magnetocrystalline anisotropy

Unusual Electronic Transport Properties in La0.96−xNdxK0.04MnO3

Polycrystalline La0.96−xNdxK0.04MnO3 has been studied by means of x-ray powder diffraction, dc magnetization, and electrical resistance measurement. La0.96−xNdxK0.04MnO3 initially crystallizes in a rhombohedral distorted perovskite structure. However, an orthorhombic structure is obtained with increasing Nd content more than 20%. Both the rhombohedral and the orthorhombic phases show ferromagnetic order. However, the compound shows a magnetic inhomogeneity behavior with increasing Nd content. With increasing Nd doping, the ferromagnetic order is significantly weakened, and the second magnetic transition occurs at a low temperature and its peak intensity enhances. The resistivity of these compounds also exhibits an imhomogeneity behavior. The rhombohedral phase shows a metal–insulator (MI) transition but the MI transition peak intensity is obviously weakened and broadens with increasing Nd content and a low temperature insulator state is observed in the orthorhombic phase. It is interesting that the second magnetoresistance ratio peak appears at low temperature. It might be due to Nd induced low temperature phase separation between the ferromagnetic metallic and antiferromagnetic insulating state

Size Induced Variations in Structural and Magnetic Properties of Double Exchange La0.8Sr0.2MnO3−δ Nano-Ferromagnet

A detailed study on the influence of particle size varied from 8 nm to 53 nm on the structural and magnetic properties of La0.8Sr0.2MnO3−δ has been done. The unit cell volume increases and the microstrain in the compound shows peak formation as the particle size decreases. Nano particles of La0.8Sr0.2MnO3−δ exhibit superparamagnetism whose blocking temperature has a nonlinear and logarithmic decreasing tendency as function of particle size and applied magnetic field, respectively. Evidence of formation of a magnetically dead layer at the surface has been found and the ratio of the thickness of the dead layer to the particle size increases exponentially with particle size. The coercivity of the nanoparicles increases manifold as particle size varies from 53 nm to 21 nm. In the single domain region the coercivity exhibits a d−1.125 behavior. The temperature dependence of the saturation magnetization shows strong collective excitation due to the spin wave that varies as Tα with α\u3eαbulk of 3/2. Thus the spin wave does not follow the Bloch law in the case of nano particles of La0.8Sr0.2MnO3−δ