%0 Journal Article
%T Magnetic and Electric Properties of , ( ) Layered Perovskites
%A A. I. Ali
%A A. Hassen
%J Advances in Condensed Matter Physics
%D 2013
%I Hindawi Publishing Corporation
%R 10.1155/2013/714143
%X The electric and magnetic properties of layered perovskites have been investigated systematically over the doping range . It was found that both Sr1.5Y0.5CoO4 and Sr1.4Y0.6CoO4 undergo ferromagnetic (FM) transition around 145£¿K and 120£¿K, respectively. On the other hand, Sr1.3Y0.7CoO4 and Sr1.2Y0.8CoO4 compounds showed paramagnetic behavior over a wide range of temperatures. In addition, spin-glass transition ( ) was observed at 10£¿K for Sr1.3Y0.7CoO4. All investigated samples are semiconducting-like within the temperature range of 10¨C300£¿K. The temperature dependence of the electrical resistivity, , was described by two-dimensional variable range hopping (2D-VRH) model at 50£¿K < ¡Ü 300£¿K. Comparison with other layered perovskites was discussed in this work. 1. Introduction Cobalt oxides have particular interest, not only because of the unique features of Co ions, but also due to their technological applications, such as solid oxide fuel cells and membranes for gas separation [1¨C5]. Double-exchange interaction between is known to be ferromagnetism (FM) while superexchange (SE) interaction between Co ions with the same oxidation of states is antiferromagnetism (AFM) [6¨C10]. The spin states of Co ions exhibit several possible spin states: low-spin ( ), intermediate-spin ( ), or high-spin ( ) for ions and ( ), ( ), or ( ) for ions. All spin states of or ions are possible because the crystal-field splitting energy of -state electrons ( ) and Hund energy ( ) are comparable for perovskite cobaltates. This implies that the energy gap between the and states is small and the electrons in can be thermally exited into the state. As a result, it is difficult to determine the spin states of these ions in cobalt oxides. In other words, complex magnetic properties arise not only in the original perovskite compounds ( is the rare earth ions) which exhibit a rather isotropic 3D arrangement of magnetic ions, but also in layered perovskite systems, , , Nd or Pr. The layered-type cobaltates with structure are characterized by two-dimensional confinement of the B-O-B network that significantly reduces the electron bandwidth. In turn, electron correlations are strong and can alter the interplay between the different microscopic degrees of freedom (lattice charge, orbital, and spin degrees of freedom). For instance, the magnetic state of the compounds transforms from AFM to FM upon doping for [11]. On the other hand, the zero field susceptibility of ( ) shows different magnetic transitions [12]. The first is due to spin-glass (SG) transition at 18£¿K as reported for layered
%U http://www.hindawi.com/journals/acmp/2013/714143/