Optical Studies Of Ordering Phenomena In Manganese Oxides

Metal oxides constitute one of the most amazing classes of materials with a wide range of properties. They exhibit a variety of phenomena, such as ferroelectricity, ferromagnetism and superconductivity. A new aspect of metal oxides — colossal magnetoresistance exhibited by certain manganese oxides, in particular rare earth manganates of perovskite structure — has received much attention in the last four years. Some of these oxides show 100% magnetoresistance and have much potential for technological applications. Previously this phenomenon was found only in layered and granular metallic materials. Studies of colossal magnetoresistance have led to the discovery of many other new phenomena and properties such as charge ordering and orbital ordering. In view of the importance of colossal magnetoresistance, charge ordering and related phenomena exhibited by oxides to the physics and chemistry of solid materials, it is necessary and timely to have a book dealing with these topics. This book begins with a review of the subject followed by contributions from a number of experts which cover the present status of the subject. Contents:Colossal Magnetoresistance, Charge Ordering and Other Novel Properties of Manganates and Related Materials (C N R Rao & A K Raychaudhuri)The Important Role of Crystal Chemistry upon the CMR Properties of Manganites (B Raveau et al.)Magnetotransport and Magnetoelastic Effects in Manganese Oxide Perovskites (M R Ibarra & J M De Teresa)Colossal Magnetoresistive Manganites: The Push Towards Low Field Magnetoresistance (R Ramesh et al.)Low-Field Magnetoresistance Induced by Grain Boundaries in Doped Manganese Perovskites (A Gupta)Colossal Magnetoresistance Without Double-Exchange: Pyrochlores (M A Subramanian et al.)First Order Insulator-Metal Transitions in Perovskite Manganites with Charge-Ordering Instability (H Kuwahara & Y Tokura)Striped Charge and Orbital Ordering in Perovskite Manganites (S W Cheong & C H Chen)Electronic Structure of Perovskite-Type Manganese Oxides (A Fujimori et al.)Spin-Valve Effect in Manganese Oxide Perovskites: CMR (N Kumar et al.)Theory of Colossal Magnetoresistance: Some Questions (T V Ramakrishnan) Readership: Students and researchers in solid state chemistry, condensed matter physics, solid state physics and materials science. keywords:Rare Earth Manganites;Manganese Oxides;Colossal Magnetoresistance;Magnetic Properties of Oxides

Interest in the transition metal oxides with perovskite related structures goes back to the 1950s when the sodium tungsten bronzes NaxWO3 were shown to be metallic [1 ], the system Lal_xSr MnO3 was found to contain a ferromagnetic conductive phase [2], and La0.sSr0.sCoO3 was reported to be a ferromagnetic metal, but with a peculiar magnetization of 1.5 #a/Co atom [3]. Stoichiometric oxide perovskites have the generic formula AMO3 in which the A site is at the center of a simple cubic array of M sites; the oxide ions form (180 ° 4)) M O M bridges to give an MO3 array of corner shared MO6/2 octahedra and the larger A cations have twelvefold oxygen coordination. Mismatch between the A O and M O equilibrium bond lengths introduces internal stresses. A compressive stress on the MO3 array is accommodated by a lowering of the M O M bond angle from 180 ° to (180 ° 4)); a tensile stress on the M O M bonds is accommodated by the formation of hexagonal polytypes [4].

Metal oxides constitute one of the most amazing classes of materials with a wide range of properties. They exhibit a variety of phenomena, such as ferroelectricity, ferromagnetism and superconductivity. A new aspect of metal oxides -- colossal magnetoresistance exhibited by certain manganese oxides, in particular rare earth manganates of perovskite structure -- has received much attention in the last four years. Some of these oxides show 100% magnetoresistance and have much potential for technological applications. Previously this phenomenon was found only in layered and granular metallic materials. Studies of colossal magnetoresistance have led to the discovery of many other new phenomena and properties such as charge ordering and orbital ordering. In view of the importance of colossal magnetoresistance, charge ordering and related phenomena exhibited by oxides to the physics and chemistry of solid materials, it is necessary and timely to have a book dealing with these topics. This book begins with a review of the subject followed by contributions from a number of experts which cover the present status of the subject.