Magnetic and Magnetoresistive Properties of Nanocrystalline Pr1−xAxMn1−yCoyO3 (A = Sr, Ca; x = 0.3, y = 0.5)
18 Oct 2010-Vol. 1276, Iss: 1, pp 368-373
TL;DR: In this article, Nanocrystalline Pr1−xAxMn1−yCoyO3 samples are prepared by sol-gel method and the XRD pattern shows single phase and cubic crystal structure with a size of 3.862 nm at room temperature.
Abstract: Nanocrystalline Pr1−xAxMn1−yCoyO3 (A = Sr, Ca; x = 0.3, y = 0.5) samples are prepared by sol‐gel method. The XRD pattern show single phase and cubic crystal structure with a ( = b = c) = 3.862 nm at room temperature. The crystallite size of the samples are calculated using Scherrer formula and found to be ∼15 nm and ∼24 nm for Pr0.7Sr0.3Mn0.5Co0.5O3 and Pr0.7Ca0.3Mn0.5Co0.5O3 respectively. The SEM images show the particles are spherical in shape and average particles sizes are about ∼20 nm and ∼25 nm. The samples undergo paramagnetic to ferromagnetic transition about ∼172 K and ∼153 K. The temperature dependence of resistivity (ρ) data show insulating behaviour below 80 K and from 80 K to 300 K, the samples behave like semiconductor. Variable range hopping conduction is found to be dominating for temperatures above 80 K. The maximum magnetoresistance is found to be ∼35% and ∼24% at 100 K and it has negative sign.
01 Jan 1974
TL;DR: In this article, a discussion is given of some aspects of the metal insulator transition and the status of the "minimum metallic conductivity" is discussed, and the concept is valid for liquids and in some, but not all, solid systems.
Abstract: A discussion is given of some aspects of the metal insulator transition. Particular attention is paid to the status of the “minimum metallic conductivity”. The concept is valid for liquids, and in some, but not all, solid systems.